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' LIBRARY
Wm Michigan State
3 University
2 or]

This is to certify that the
dissertation entitled

INFLUENCE OF A DEXTERITY TRAINING PROTOCOL ON
BIOMECHANICAL PARAMETERS OF THE KNEE JOINT AMONG
ADOLESCENT FEMALE BASKETBALL PLAYERS

presented by

Anthony Moreno

has been accepted towards fulfillment
of the requirements for the

Doctoral degree in Kinesiology

 

 

 

(/ Major Professor’s Signature

flz/ujwé 2,1) Lor/

 

Date

MSU is an Affirmative Action/Equal Opportunity Institution

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DATE DUE

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2/05 p:/CIRC/DateDuetindd-p.1

 

INFLUENCE OF A DEXTERITY TRAINING PROTOCOL ON BIOMECHANICAL
PARAMETERS OF THE KNEE JOINT AMONG ADOLESCENT FEMALE
BASKETBALL PLAYERS
By

Anthony Moreno

A DISSERTATION

Submitted to
Michigan State University
In partial fulfillment of the requirements
For the degree of

DOCTOR OF PHILOSOPHY
Department of Kinesiology

2006

BIO

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ABSTRACT
THE INFLUENCE OF A DEXTERITY TRAINING PROTOCOL ON
BIOMECI-IANICAL PARAMETERS OF THE KNEE JOINT AMONG ADOLESCENT
FEMALE BASKETBALL PLAYERS
By
Anthony Moreno

The purpose of this study was to examine the effects of a dexterity protocol on
biomechanical parameters of the knee joint among competitive adolescent female
basketball athletes landing on a force platform from a maximal vertical jump effort, and
subsequently performing an unanticipated directional sprint task. Peak ground reaction
forces (PGRF), peak knee joint flexion (PKJF), time to peak knee joint flexion (TKJF),
and peak knee extension moments (PKJM) were collected among Six adolescent female
basketball players fiom two randomly solicited elite-for-age teams placed into two
groups, experimental (n=4; mean = 13.75 yr.) and control (n=2; mean age = 13.85yr.). In
addition to their regular practice and competition schedule, the experimental group was
exposed to a Six week dexterity training intervention, while controls followed their
typical practice and competition routine.

Pre-intervention dependent variables were analyzed with an independent sample
t-test and revealed TKJ F exhibited the lone significant pre-existing group difference with
the unanticipated landing condition. Post intervention biomechanica] parameters for both
anticipated and unanticipated landing conditions were calculated and evaluated through
the use of descriptive statistics. To test the hypotheses related to potential group

differences over time, a series of repeated-measures analysis of variance (ANOVAS),

utilizing a mixed model analysis, was performed for each of the dependent variables. For

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the unanticipated vertical jump landing condition, results of the ANOVAS revealed no
significant main effect of the dexterity protocol for mean PGRF, PKJF, TKJF, and
PKJM.

Pearson’s correlations were performed to determine if relationships among the
dependent variables existed, with both unanticipated and anticipated conditions.
Unanticipated PKJ F and unanticipated TKJF exhibited a moderately strong relationship
(r = .72, p< .01), while anticipated TKJF exhibited a moderate association with
anticipated PKJ F (r = .58, p< .01) and a moderate inverse relationship with anticipated
PKJ M (r = - .58, p< .01 ). To determine if significant pre-intervention differences existed
between the anticipated and unanticipated landing condition among all participants, a
paired sample t-test was conducted for each dependent variable. Mean values for PGRF,
PKJF, TKJ F, and PKJM were significantly different when comparing the anticipated to
the unanticipated landing condition implying the use of different landing strategies with
unpredictable Situations.

Despite the lack of Significance among the dependent variables with the
unanticipated landing condition, mean values for PKJF and TKJF did exhibit
hypothesized trends in that the six week dexterity protocol would respectively generate
increases in peak knee joint angular excursion and time to peak knee joint flexion, upon
impact with the force platform. Future investigations should further explore potential
disparities among anticipated and unanticipated landing scenarios to examine if anterior
cruciate ligament (ACL) injury intervention protocols must provide greater variability
and unpredictability, thus, lending greater insight in the attempt to manage those extrinsic

factors associated with non-contact ACL injury among adolescent female athletes.

DEDICATION

This dissertation is dedicated to my parents, Frances L. and Ricardo G. Moreno.

iv

ACKNOWLEDGEMENTS

Foremost, I would like to thank David Mullineaux Ph.D. for his input, guidance,
and technical assistance throughout all stages of this dissertation. This research project
could not have been accomplished without his selfless permission, support, and time. I
would also like to thank and recognize the significant contributions of my dissertation
committee, John Haubensticker Ph.D., Tracey Covassin Ph.D., and Mark Reckase Ph.D.

I would like to express my sincere gratitude to Eugene Brown Ph.D., my major
advisor, for his acceptance, patience, confidence, and guidance throughout my doctoral
studies and for providing me the opportunity to become a new investigator and better
teacher. Special thanks to Miguel Narvaez, Kris Kotrola, Lynette Craft Ph.D., and Adam
Bruenger for their time and assistance throughout all stages of data collection and the
preparation of this document. I would also like to recognize Gail Dummer Ph.D., Robert
“Bob” Malina Ph.D., and Vern Seefeldt Ph.D. for Sharing their time, insight, and research
experiences with both able-bodied and disabled youth during my tenure as a doctoral
student.

Finally, thank you to my sons, Colton and Cade, who give me the energy and
inspiration to try to be the best I can be every single day, and last but definitely not the
least, my wonderful wife Tracy, for her tolerance and continuous support of all my

personal endeavors throughout the years. Thank you.

 

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TABLE OF CONTENTS

LIST OF TABLES ................................................................................. viii

LIST OF FIGURES ................................................................................... x
CHAPTER 1

INTRODUCTION ................................................................................... 1

Overview of the Problem ................................................................... 1

Significance of the Problem ................................................................ 1

Statement of the Problem ................................................................... 4

Need for the Study ............................................................................ 4

Hypotheses ................................................................................... 6

Limitations .................................................................................... 7

Assumptions .................................................................................. 7

Definitions .................................................................................... 9
CHAPTER 2

REVIEW OF LITERATURE ...................................................................... 19

Function of the ACL ....................................................................... 21

Mechanism of Injury ....................................................................... 25

Intrinsic and Extrinsic Factors Associated with ACL Injury ......................... 29

Intrinsic Factors ................................................................... 30

Anatomical Factors ...................................................... 3O

Q—angle ............................................................ 3 1

Femoral Anteversion ............................................ 34

Intercondylar Notch Width ..................................... 37

Summary of Anatomical Factors ....................................... 38

Hormonal Factors ......................................................... 41

Summary of Hormonal Factors ......................................... 43

Extrinsic Factors .................................................................. 44

Muscle Strength and Recruitment ...................................... 45

Knee Joint Kinematics and Ground Reaction Forces ............... 46

Knee Joint Extensor Moments .......................................... 51

Summary of the Extrinsic Factors ...................................... 53

Functional Joint Stability, Muscle Stifi‘ness, and Kinesthesia ........................ 55

Neuromuscular Intervention .............................................................. 58

Movement Competence ............................................................ 62

T raining for Dexterity ...................................................................... 66
CHAPTER 3

METHODS ........................................................................................... 71

Experimental Design ....................................................................... 71

Participants .................................................................................. 7 1

vi

 

 

 

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Session I : Parent/Participant Informative Practice Session ........................ 74

Session 2: Anthropometric/ Vertical Jump Session .................................... 74
Maturity Assessment .............................................................. 75
Vertical Jump Test ................................................................ 76
Session 3: Pre-intervention Data Collection Session ................................. 79
Pre-intervention Data Collection with Anticipated Conditions... ....83
Pre-intervention Data Collection with Unanticipated Conditions. . . .......9O
Dexterity Intervention ..................................................................... 93
Post Intervention Data Collection with Anticipated and
Unanticipated Conditions ........................................................ 94
Data Analyses .............................................................................. 94
CHAPTER 4
RESULTS ............................................................................................ 96
CHAPTER 5
DISCUSSION ...................................................................................... 102
Peak Ground Reaction Force ........................................................... 102
Peak Knee F lexion on Impact ........................................................... 107
Time to Peak Knee F lexion on Impact ................................................. ll 1
Peak Knee Extensor Moment on Impact ............................................... 1 14
Anticipated Versus Unanticipated Landing Conditions ............................. 129
The Role of Unanticipated Training .................................................... 136
Dexterity in the Context of A CL Injury Prevention for the Female
Athlete ............................................................................. 137
Physical Growth and Maturation ...................................................... 139
CHAPTER 6
SUMMARY AND RECOMMENDATIONS ................................................. 143
Summary ................................................................................... 143
Recommendations ........................................................................ 146
APPENDICES ...................................................................................... 149
A: IRB Approval ......................................................................... 150
B: Physical Maturity Assessment ...................................................... 158
C: Dexterity Protocol Skills ............................................................. 160
D: Dexterity Training Program ......................................................... 165
E: Participant Body Segment Parameters for Inverse Dynamics Procedure. . l 72
F: MATLAB Source Code for Inverse Dynamics Procedures ..................... 174
G: Participant Mean Value Data for the Dependent Variables ..................... 186
REFERENCES ..................................................................................... 195

vii

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Table 1

Table 2

Table 3

Table 4

Table 5

Table 6

Table 7

Table 8

Table 9

Table 10

Table 11

Table 12

Table 13

Table 14

Table 15

Table 16

Table 17

LIST OF TABLES
Participant Anthropometric Characteristics and Maturity Status .......... 73

Results for the Dependent Variables Following a Maximal Vertical
Jump Landing with Unanticipated Landing Conditions... .....98

Means and Standard Deviations of the Dependent Variables
with Anticipated Conditions ............................................. 99

Means and Standard Deviations of the Dependent Variables with
Unanticipated Conditions ................................................ 100

Pearson ’s Correlations for Dependent Variables for Anticipated
and Unanticipated Conditions ......................................... 101

Mean Peak Ground Reaction Force on Impact for All

Participants . . . .............................................................................. 106
Mean Peak Knee F lexion on Landing for All Participants ................. 1 10
Mean Time to Peak Knee F lexion on Impact for All Participants ........... 113
Mean Peak Right Knee Extensor Moment for All Participants ............ l 17
Dexterity Protocol: Week #1 .................................................... 166
Dexterity Protocol: Week #2 .................................................... 167
Dexterity Protocol: Week #3 .................................................... 168
Dexterity Protocol: Week #4 .................................................... 169
Dexterity Protocol: Week #5 .................................................... 170
Dexterity Protocol: Week #6 .................................................... 171

Whole Body and Lower Extremity Anthropometric Parameters
of Stature, Body Mass, and the Right Thigh, Shank, and Foot
forAll Participants.........................................................173

Pre-intervention Mean Values for the Dependent Variables of

Each Subject during Landing with Anticipated
Conditions ................................................................. 1 87

viii

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Table 18

Table 19

Table 20

Table 21

Table 22

Table 23

Table 24

Pre-intervention Mean Values for the Dependent Variables
of Each Subject during Landing with Unanticipated

Conditions ........................................................................

Post Intervention Mean Values for the Dependent Variables
of Each Subject during Landing with Anticipated

Conditions after ...................................................

Post Intervention Mean Values for the Dependent Variables
of Each Subject during Landing with Unanticipated
Conditions...

Mean Peak Ground Reaction Force on Impact ..
Mean Peak Knee Flexion on Landing...

Mean Time to Peak Knee Flexion on Impact

Mean Peak Right Knee Extensor Moment... ....... .

ix

......... 188

....... 189

...190

191

192

...193

..194

 

 

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Figure 1
Figure 2
Figure 3

Figure 4

Figure 5

Figure 6
Figure 7
Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 1 7

LIST OF FIGURES

Anterior view of the right knee joint ............................................ 23
Superior view of the right knee joint ............................................. 24
External tibial rotation at the right knee relative to the femur. . . . ........26

Normal neutral position (A) and the “Position of no return” exhibiting
excessive femoral anteversion, external tibial rotation, and
concurrent foot pronation (B) .......................................... 27

Anterior tibial drawer effect enhances the conditions for partial or
complete mechanical failure of the anterior cruciate ligament ..... 28

Q-angle ............................................................................. 33
View of the right femur showing femoral anteversion ....................... 36
Notch width index (NW1) ........................................................ 39
Intercondylar notch Shapes ........................................................ 40
Assessment of participant maximum standing reach used in the
determination of maximum vertical jump height. .. ..................... 78
Retroreflective marker set-up for kinematic data collection ................. 8O

Schematic of laboratory instrumentation for biomechanical
data collection ............................................................. 81

Subject assumes the “ready” position with the right foot in
contact with the force platform prior to a jump trial ................. 86

Transcribed “X” located on each subject’s designated acrylic
vane of the VertecTM ....................................................................... 87

View of the testing area and position of the Vertecm in
proximity to the force platform .......................................... 88

Landing area with the right foot placed on the force platform .............. 89

Research assistant in position to provide the directional cue for the
subject with the unanticipated condition .............................. 91

 

 

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Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Research assistant providing the left directional cue for the
unanticipated condition ................................................ 92

Mean normalized peak ground reaction force on impact
for the experimental group ........................................... 121

Mean normalized peak ground reaction force on impact
for the control group ................................................... 122

Mean peak flexion of the right knee on impact
for the experimental group ........................................... 123

Mean peak flexion of the right knee on impact
for the control group .................................................. 124

Mean time to peak right knee flexion on impact
for the experimental group ........................................... 125

Mean time to peak right knee flexion on impact
for the control group .................................................. 126

Mean peak normalized right knee extensor moment on
impact for the experimental group .................................... 127

Mean peak normalized right knee extensor moment on
impact for the control group ........................................... 128

Mean normalized pre-intervention peak ground reaction force
on impact: Anticipated versus unanticipated conditions
for all participants ....................................................... 132

Mean pre-intervention peak flexion of the right knee
on impact: Anticipated versus unanticipated conditions
for all participants ....................................................... 133

Mean pre-intervention time to peak right knee flexion on impact:
Anticipated versus unanticipated conditions
for all participants ....................................................... 134

Mean pre-intervention peak normalized right knee extensor

moment on impact: Anticipated versus unanticipated
conditions for all participants ........................................... 135

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CHAPTER 1
INTRODUCTION
Overview of the Problem
Anterior cruciate ligament (ACL) injuries are among the most devastating and
frequent injuries encountered in recreation, sport, and workplace. Current
epidemiological data reports the incidence of ACL injury to occur to one in every 3000
persons, with approximately 70% of these related to sports participation (Chappell, Yu,
Kirkendall, & Garrett, 2002; Colby, Francisco, Yu, Kirkendall, Finch, & Garrett, 2000;
Huston, Greenfield, & Wojtys, 2000). Of great concern is the fact that the incidence of
non-contact ACL injuries is two to eight times greater among female participants when
compared to their male counterparts competing in Similar sports (Malinzak, Colby,
Kirkendall, Yu, & Garrett, 2001; Harmon & Ireland, 2000; Kirkendall & Garrett, 2000;
Hewett, 2000; Heidt, Sweeterman, Carionas, Traub, & Tekulve, 2000; Hosea, Carey, &
Harrer, 2000; McLean, Neal, & Myers, 1999; Demont, Lephart, Giraldo, Swanik, & Fu,
1999; Heitz, Eisenman, Beck, & Walker, 1999; Huston & Wojtys, 1996; Ireland, 1999;
Arendt & Dick, 1995).
Significance of the Problem
Injuries sustained with high frequency and severity may develop into medical
scenarios that generate into important health concerns. The National Collegiate Athletic
Association (NCAA) has documented an average knee injury rate of ten% among female
participants, and given there are approximately 130,000 female intercollegiate athletes

participating each year in the NCAA, it can be estimated that approximately 13,000 ACL

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injuries of varying severity may occur to these female participants at the intercollegiate
level (NCAA, 1997).

In 1997, the National Federation of State High School Associations reported more
than 2.5 million girls participate in high school sports programs during the course of a
given year. Although the rate of knee injury for most female participant sports is not
known for high school populations, if they approximate those at the intercollegiate level
on the basis Of NCAA incidence figures, it is estimated that 25,000 ACL injuries could
occur among the 2.5 million participants over one year (Huston et al., 2000).

Hewett et a1. (1999) has reported that, for female participants of high school
basketball, ACL injuries occur at an annual rate of approximately one in 65 participants.
In 2002, the National Federation of State High School Associations reported 452, 728
female basketball players participated at the high school level in the United States. Given
the incidence figures reported by Hewett et a1. (1999), it is estimated that approximately
7,000 ACL injuries may occur to female high school basketball athletes on an annual
basis.

Powell and Barber-Foss (2000), in a cohort observational study utilizing certified
athletic trainers, found the rate of female high school athletes to undergo ACL surgical
procedure four times as often as their male counterparts and were 44% more likely to
injure the ACL than their male counterparts. They also found injury rates, knee surgery
rates, and, Specifically ACL surgery rates for girls’ high school basketball players, similar
to those rates found for women participating at the levels of intercollegiate and Olympic
basketball. In concert with epidemiological studies conducted at the intercollegiate level,

the investigators of this study found high school basketball to not be a unique sport in the

 

 

 

 

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incidence and severity of ACL injuries when comparing the frequency to their male
counterparts. When identifying patterns by sport, soccer possesses similarities to
basketball in that females exhibit Significantly higher ACL injury rates when compared to
their male counterparts (Powell & Barber-Foss, 2000).

These findings support the hypothesis that there is greater risk of knee injury and
knee surgery for female athletes at the competitive intercollegiate and high school levels.
This manifest difference in injury rate of the ACL between females and males has
spurred efforts by researchers to determine why there is such disparity between genders.
This issue is given greater Significance since the passage of Title IX in 1972 as a federal
mandate that has dramatically expanded the number of opportunities for females in sport
from the recreational youth level to professional Sport. In conjunction with these higher
participation rates comes the realization that these same opportunities enhance the
potential for increasing the quantity of serious knee injuries (Hosea et al., 2000; Hewitt,
2000; Powell & Barber- Foss, 2000; Delfico & Garrett, 1998).

Hutson et a1. (2000) reported the average monetary cost per ACL surgery and
rehabilitation to be approximately $17,000 in the United States. Based upon injury
estimates from Hewett et a1. (1999), it is estimated that ACL injuries among female
athletes at the high school level have the potential to cost approximately $119 million
dollars on an annual basis. These figures do not reflect the costs associated with other
lower extremity anomalies (e.g., stress fractures of the foot, ankle injuries) and it must be
considered that these incidents contribute to other costly and rehabilitative conditions
such as emotional distress, depression, poor academic performance, unstable mental

health, and post traumatic arthritis (Shea, Apel, & Pfeiffer, 2003; Hewett, 2000).

 

 

 

 

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Statement of the Problem

The purpose of this study was to examine the effects of a dexterity training
intervention on peak ground reaction forces (PGRF), peak knee joint flexion (PKJF), time
to peak knee joint flexion (TKJ F), and peak knee extension moments (PKJM) of
competitive adolescent female basketball athletes landing on a force platform from a
maximal vertical jump effort and immediately performing an unanticipated directional
sprint task.

Need for the Study

A review of the pertinent epidemiological literature with respect to ACL injury
has revealed that there are several potential injury mechanisms that may play a vital role
in defining the significant gender disparity Observed in sports-related non-contact ACL
injury rates (Hewett, Myer, & Ford, 2006; McClean, et al., 1999). These proposed injury
mechanisms are typically categorized as intrinsic or extrinsic factors (Hewett et al., 2006;
Huston et al., 2000).

Intrinsic factors are those features that include intra-individual characteristics
such as grth and maturation, lower extremity Skeletal misalignment, insufficient
muscular strength, poor joint mobility, excessive joint laxity, and hormonal mechanisms.
Intrinsic factors are typically difficult to control and may not be modifiable (Harmon &
Ireland, 2000). Unlike intrinsic factors, extrinsic factors may be modifiable and include
such mechanisms as neuromuscular proficiency, individual motor competence, musculo-
skeletal agonist-antagonist joint strength ratios, supervision and instruction, playing
surface, level of competition, and equipment (Hutson et al., 2000). Although it is

generally understood that these intrinsic and extrinsic mechanisms are interdependent, the

 

 

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interactions between learning and coaching environment, physical structure and
endocrine systems can be extremely influential on neuromuscular function, bone growth,
and ligamentous integrity (Fulkerson & Arendt, 2000).

Although the quantity of biomechanical studies regarding ACL injury has
increased, those specifically involving female adolescent athletic populations are sparse.
Despite the fact that great strides have been accomplished in achieving greater
understanding into the ACL injury gender-bias (Hewett, 2000; Harmon & Ireland, 2000;
Huston & Wojtys, 1996; Ireland, 1999; Arendt & Dick, 1995), the vast majority of these
research efforts have utilized intercollegiate or adult populations to support the findings.
The available data on adolescent female athletes is lacking and remains a population from
which greater information should be collected and analyzed with respect to their differing
and dynamically maturing anatomical and physiological systems, when compared to their
physically advanced intercollegiate peers.

Because intrinsic factors (e. g., anatomical and/or hormonal characteristics) cannot
be viably addressed in the field setting, research emphases have shifted toward
understanding the influence of agility, perturbation, and plyometric training protocols that
provide the opportunity to alter lower extremity neuromuscular strategies and potentially
play a role in modifying the extrinsic factors (e. g., muscle activity and/or gross motor
competence). This study will address the influence of a dexterity protocol on
biomechanical parameters of the knee joint. In addition, it is the intent of this research
paradigm to determine if there are potential “windows” of opportunity at particular
developmental ages where neuro-mechanical pliability can be enhanced. In particular, at

ages where dynamic morphological and physiological changes are concurrent with the

 

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acquisition of fundamental and special motor skills that may play a vital role in
modifying those special biomechanical parameters associated with ACL injury.

The utility of introducing physical training protocols at a developmental age may
provide a reliable intervention method through which the alarming ACL injury gender-
bias can be potentially attenuated. Further, the opportunity to administer those
interventions in sufficient doses at dynamic stages of growth and development may
mitigate the incidence of non-contact ACL injuries among those female athletes that
intend to participate in competitive or recreational play throughout high school, college,
and adulthood. .

Hypotheses
The previously presented research paradigm suggests the following four research

hypotheses:

Hypothesis 1 . In comparison to controls, participants of the experimental group will
exhibit lower ground reaction forces at landing under unanticipated conditions after
following the twice per week, six week dexterity training protocol.

Hypothesis 2. In comparison to controls, participants of the experimental group will
exhibit greater angular ranges of knee joint flexion on landing under unanticipated
conditions after following the twice per week, six week dexterity training protocol.
Hypothesis 3. In comparison to controls, participants of the experimental group will
exhibit greater time to maximum knee joint flexion on landing under unanticipated

conditions following the twice per week, six week dexterity training protocol.

Hypothesis 4. In comparison to controls, participants of the experimental group will

exhibit decreased peak extensor moments of the knee joint on landing under

unanticipated conditions following the twice per week, six week dexterity training

protocol.

Limitations
The participants of this study compete in an Amateur Athletic Union (AAU)
basketball league and are considered to possess superior basketball Skills when
compared to their age-group peers. Thus, the participants of this study may not be
representative of all adolescent female basketball players that compete at other
levels.
For this study, the influence of a dexterity training program on the hypothesized
dependent variables was conducted with a relatively small sample Size.
Limitations with respect to sample size make it arduous to interpret the results of
the data analysis.

Assumptions

The following assumptions with respect to the participants and the research design

were made to draw conclusions from the results.

The participants of the study were representative of other elite female adolescent
basketball players who participate in an AAU competitive basketball league.
Because elite-level female adolescent basketball players demonstrate superior
basketball skills, it was expected that their specialized training enabled them to
demonstrate enhanced motor ability when compared to their age-group peers at

lower levels of competitive basketball.

o The participants did not engage in any recreational or competitive physical
activity outside of practice and the preparative environment typical Of an elite

female adolescent basketball athlete.

 

 

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Definitions

Acceleration. The rate of change of velocity.

Agility. The process by which the degrees of freedom of a body segment or segments are
organized in Space and time and sequence to produce a functional motor response
to an atypical motor environment.

Analog-to-digital conversion (A/D). The process Of taking a continuous Signal and
sampling it over time to create an array of discrete digital values that represent the
original signal.

Angular acceleration. The rate of change of angular velocity.

Angular displacement. The change in angular position.

Angular velocity. The rate of change of angular displacement.

Anterior tibial drawer effect. Anterior directed translation of the tibia with respect to the
position of the femur upon impact from a jump landing or a cutting-type
maneuver.

Anthropometrics. The measurement of physical properties associated with the human
body.

Anticipated directional sprint task. Prior to performing a maximal vertical jump effort,
the participant is made aware of the direction (left or right) with which to Sprint
two meters upon immediate contact with the laboratory floor surface.

Biomechanics. The study which applies the principles of mechanics to living things.

Center of mass/gravity. The point that represents the total weight/mass distribution of a
body. The mass centriod is the point where the mass of the object is balanced in

all directions.

Chondromalacia. Uncharacteristic softening of skeletal cartilage.

Concentric muscle action. The condition where activated muscle(s) create a torque
greater than a resistance torque resulting in a movement of a segment of the body
in the direction of the action of the muscles.

Coordination. The process by which the degrees of freedom are organized in space and
time and subsequently produce a firnctional movement pattern.

C ountermovement jump. Rapid flexion at the hip and knee, concurrent with dorsiflexion
at the ankle, that elicits eccentric loading of the lower extremity musculature
immediately prior to the concentric phase of a jump.

Cut-ofl frequency. The cutting point of a filtering technique applied to an array Of data,
where frequencies above or below a designated frequency are removed. The

lower the cut-off frequency for a low-pass filter the greater the smoothing Of the
signal.

Degrees of freedom. The number of independent movements an object or body part
(e.g., limb segment) may create, and consequently the number of measurements
necessary to document the kinematics of the object or body part.

Dexterity. The process by which the degrees of freedom of a body segment or segments
are organized in space and time and sequenced to produce if necessary, a rapid
motor solution to an unpredictable motor problem with varying spatial, temporal,
and sequential elements.

Dexterity protocol. Physical training program that includes selected motor exercises

with varying spatial, temporal, and sequential elements.

10

 

 

Digitize. The process of measuring two-dimensional locations of points on an image.

Displacement. Change in position of some point in a particular direction.

Dynamics. The branch of mechanics studying the motion of bodies under acceleration.

Dynamic restraint components. Proprioceptive components (e.g., muscle spindles, golgi
tendon organs) that regulate the activity of skeletal muscles that literally cross an
articulation to help provide functional joint stability via concentric, eccentric,
and/or isometric muscle contractions.

Eccentric muscle action. The condition where activated muscle(s) create a torque
less than a resistance torque resulting in a movement of a segment of the body in
the opposite direction of the action of the muscle(s).

Electromyography (EMG). The recording, processing, and amplification of the electrical
signal Of active muscle.

Energy (mechanical). The ability to do mechanical work.

Engram. Neural activity used in the assembly and execution of a motor pattern.

External work. Work done on a body by an external force.

Extrinsic injury factors. Extrinsic injury factors are typically modifiable and include
such areas as neuromuscular proficiency, motor competence, musculoskeletal
agonist-antagonist joint-strength ratios, supervision and instruction, playing
surface, level of competition, and equipment.

Femoral anteversion. An anatomical condition where the femoral
head and neck are rotated anterior to an imaginary line directed through the
femoral condyles in the horizontal plane.

Foot pronation. Combined eversion and abduction motions of the foot.

11

Force. An influence that either pushes or pulls and can act to alter the motion or shape of
an object.

Force platform. A complex force transducer that measures all three orthogonal forces
and moments applied to its surface.

Frame (video). One complete video image.

Genu Valgum. Anatomical condition associated with a “knock-kneed” disposition.

Genu Varus. Anatomical condition associated with a “bowlegged” disposition.

Global reference frame. Measuring kinematics relative to an unmoving coordinate
system on the earth.

Ground reaction force. Common three-dimensional force vector acting on the body that
occurs with typical standing, running, or jumping activities.

Intercondylar notch width. The distance between the two distal femoral condyles at the
level of the popliteal groove.

Intercondylar impingement. During extension of the knee, the anterior cruciate ligament
may impinge upon the area designated as the anterior intercondylar notch.

Internal work. Work done on defined systems of the body by internal forces
within these systems.

Intrinsic injury factors. Factors that include intra-individual characteristics such as
growth, maturation, lower-extremity alignment, muscular strength, joint mobility,
joint laxity, and the endocrine system.

Inverse dynamics. Biomechanical research technique used to estimate net forces and
moments in a linked segment model fiom measured kinematics, kinetics, and

anthropometric data.

12

 

 

 

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Isokinetic muscle action. That condition where the angular velocity of a segment’s
movement is constant regardless of the concentric torque produced by a muscle or
muscle group.

Isometric muscle action. The condition where activated muscle(s) create(s) a torque
equal to the resistance torque and the angular velocity of the associated segment
equals zero.

Isotonic muscle action. Dynamic condition with a constant resistance and a varying
muscle tension because of factors associated with the changing muscle moment.

Joint center. An approximation of the instantaneous center of rotation of a joint.

Kinematics. A subdivision of dynamics that is concerned with a quantitative description
of an object’s position in space, velocity, and acceleration without regard for the
forces involved.

Kinesthesia. Knowledge of one’s position and orientation of a body segment in space or
its relative position in reference to another body segment.

Kinetics. A subdivision of dynamics that is concerned with the effects of forces on some
object, segment, or body.

Lateral rotation of the knee. An outwardly-directed rotation at the knee joint with

respect to the anatomical reference position of the human body.

Load. A force or moment applied to an object.

Local reference frame. Measuring kinematics relative to a moving coordinate system on
a nearby rigid body (joint, segment, or center of mass).

Low pass filter. A signal processing technique that removes high frequency components

fi'om an array of data.

13

 

 

 

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Medial rotation. An inwardly-directed rotation at the knee joint with

respect to the anatomical reference position of the human body.

Moment (moment of force, torque). The rotational effect of a force applied to a lever.

Moment arm. The leverage of a force for creating a moment. The perpendicular distance
from the axis of rotation to the line of action of the force.

Moment of inertia. The resistance to rotation of a body.

Motor (eflerent) pathway. Neural pathway with which impulses from the brain and
Spinal cord innervate musculature and glands.

Motor unit. A motor neuron and all the muscle fibers it innervates.

Muscle stiflness. Regulated by proprioceptive feed forward and feedback mechanisms, it
is the ratio of the change in applied force per change in length of the muscle.

Neuromuscular control. The elaborate nervous and muscular mechanisms that comprise
the nervous system and delineate their role in voluntary, involuntary, and
reflexive muscle activation.

Newton (N). The metric unit of force. One Newton is equal to 0.22 pounds.

Notch width index (IVWI). Ratio determined by comparing the width of the femoral
intercondylar notch to the distance between the two distal femoral condyles at the
level of the popliteal groove.

Passive restraint components. The ligamentous and cartiligenous structures, joint
capsules, and bony arrangements about an articulation that help provide
functional joint stability.

Patello-femoral distress syndrome. Lateral deviation of the patella as it tracks in the

femoral groove.

14

Patello-femoral tracking. The appropriate anatomical and central disposition of the
patella with respect to the femoral groove of the knee joint complex.

Perturbation training. Physical training that involves the maintenance of lower extremity
balance during the disturbance of the support surfaces.

Patello-femoral tracking. Tracking of the patella within the femoral groove of the femur.

Peak ground reaction force (PGRF). The highest instantaneous ground reaction force
as participant’s of the study made contact with the force platform following a
maximal vertical jump effort.

Peak knee extension moment (PKJM). The highest instantaneous rotational force (torque) '
produced by the knee extensor musculature to oppose knee joint flexion during
landing and indicative of the muscles role as a shock absorber.

Peak knee joint flexion (PKJF). The maximum amount of knee joint displacement
with reference to the angle formed by the right thigh and lower leg segments as
participant’s of the study made contact with the force platform following a
maximal vertical jump effort.

Plyometric training. Method of physical training technique used to enhance muscular
power utilizing a rapid stretch-shortening contraction of a muscle or muscle group
to entice greater rate of force development.

“Position of no return Jump landing condition that exhibits simultaneous femoral
anteversion, external tibial rotation, and foot pronation.

Power (mechanical). The rate of doing mechanical work that represents the product

of force and velocity. Power can be calculated as Work/Time or Force x Velocity.

15

 

 

 

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Proprioception. The culmination of all sensory inputs originating from the visual
apparatus, vestibular system, and peripheral mechanoreceptors of various
musculoskeletal structures.

Q-angle. The Q- or quadriceps angle is defined as the acute angle between the line
connecting the anterior suprailiac spine (A818) and the midpoint of the patella,
and the line connecting the tibial tuberosity with that same patellar reference
point.

Quickness. The process by which the degrees of freedom of a body segment or segments
are organized in space and time and sequence to produce a rapid functional motor
response to an atypical motor environment.

Recruitment. The activation of motor units within muscles by the central nervous system.

Reflective markers. Hi gh-contrast reflective materials attached to subjects to facilitate
the location of segments or joint centers for digitizing the locations of these
segments or joints in flames of video.

Rigid body. Mechanical simplification (abstraction) assuming the dimensions of an
object do not change during movement and loading.

Sampling rate. The number of discrete samples per second used to represent a
continuous Si gnal.

Sensorimotor system. Neurological apparatus responsible for the regulation of the
interaction between the sensory (afferent) and motor (efferent) pathways.

Sensory (aflerent) pathway. Neural pathway with which impulses from peripheral

sense organs, skin, and viscera are directed to the brain and spinal cord.

16

Shear. Mechanical loading in opposite directions and at right angles to the surface of a
material.

Skeletal dimorphism. Differences among Skeletal bone structures typically defined by
sex (male or female) and/or behavior.

Statics. The branch of mechanics studying bodies at rest or uniform motion.

Strain. The amount of deformation of a material by an applied force, usually expressed
as a percentage change in the original dimensions of the material.

Strength (muscular). The maximum force or torque produced by a muscle or muscle
group at a specific joint angle. Research has found several domains of strength
expression depending on the time, velocity, and resistance involved.

Stress (mechanical). The force per unit area expressed upon an object.

Stretch-shortening cycle (SSC). Muscle agonists for a movement are eccentrically loaded
during a countermovement, and immediately before the concentric action. SSC
enables greater initial force and concentric work than concentric actions alone.

Tension. Mechanical loading created by forces in opposite and non-centric directions
acting along a longitudinal axis.

Time to peak knee joint flexion (T KJF ). The recorded time (sec.) for each participant,
commencing with initial contact with the force platform until peak knee joint
flexion, upon performing a maximal vertical jump effort.

Unanticipated directional sprint task. Prior to performing a maximal vertical jump
effort, the participant is not aware of the direction (left or right) with which they

are to sprint two meters upon immediate contact with the laboratory floor surface.

17

 

 

 

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”bi

Valgus stress. Inward or knock-kneed predisposition that places mechanical stress on
medial structures Of the knee joint.

Varus stress. Outward or bow-legged predisposition that places mechanical stress on
lateral structures of the knee joint.

Vector. A complex quantity expressing magnitude and direction (e.g., force, velocity).

Weight. Vertical resistance of a mass due to gravitational force.

Work (mechanical). Positive work is done when a force moves an object in the direction

of the force and is calculated by the product of force and displacement.

18

CHAPTER 2
REVIEW OF LITERATURE

Current epidemiological data reports the incidence of ACL injury to occur to one
in every 3,000 persons, with approximately 70% of these related to Sports participation
(Chappell et al., 2002; Colby et al., 2000; Huston et al., 2000). For female participants of
recreational and competitive sport, these figures become even more alarming when the
prevalence of non-contact ACL injury is two to eight times greater when compared to
their male counterparts competing in similar sports (Malinzak et al., 2001; Harmon &
Ireland, 2000; Kirkendall & Garrett, 2000; Hewett, 2000; Heidt et al., 2000; Hosea et al.,
2000; McLean et al., 1999; Demont et al., 1999; Heitz et al., 1999; Huston & Wojtys,
1996; Ireland, 1999; Arendt & Dick, 1995).

The passage of Title IX of Education Amendments in 1972 as a federal mandate
has dramatically increased the number Of opportunities for girls and women in sport.
Today, women comprise 35% of the total intercollegiate participants compared to only
15% in 1972. In conjunction with these higher participation rates comes the realization
that these same opportunities enhance the potential for increasing the quantity of serious
knee injuries (Hosea et al., 2000). Injuries sustained with high frequency and severity
can generate medical scenarios that develop into important health concerns. The NCAA
documented an average knee injury rate of 10% for female athletes within one year.
Given there are approximately 130,000 female intercollegiate athletes, approximately
13,000 ACL injuries of varying severity may occur to females that participate at the

intercollegiate level (NCAA, 1997).

19

In 1997, the National Federation of State High School Associations reported more
than 2.5 million girls participate in high school sports programs during the course of a
given year. Although the rate of knee injury for most fernale-participant sports is not
known for high school populations, if they approximate those at the intercollegiate level
on the basis of NCAA incidence figures, it could be estimated that 25,000 ACL injuries
may occur among the 2.5 million participants (Huston et al., 2000).

Hewett et a1. (1999) has reported that, for female participants of high school
basketball, ACL injuries occur at an annual rate of approximately one in 65 participants.
In 2002, the National Federation of State High School Associations reported 452, 728
female basketball players participated at the high school level in the United States. Given
the incidence figures reported by Hewett et a1. (1999), it is estimated that approximately
7,000 ACL injuries may occur to female high school basketball athletes on an annual
basis.

Huston (2000) reported the average monetary cost of ACL surgery and
rehabilitation to be approximately $17,000 in the United States. Based upon injury
estimates from Hewett et a1. (1999), it is estimated that ACL injuries among female
athletes at the high school level have the potential to cost approximately $119 million
dollars on an annual basis. These figures do not reflect the costs associated with other
lower extremity orthopedic anomalies (e.g., stress fractures of the foot, ankle injuries),
and it must be considered that these incidents contribute to other costly rehabilitative
conditions such as emotional distress, depression, poor academic performance, unstable

mental health, and post traumatic arthritis (Shea et al., 2003; Hewett, 2000).

20

Because of the steady increase in the number of females participating in Sport,
there exists a potential for these conditions to become further exacerbated. To help
decrease this potential, it becomes necessary to fully understand those environmental,
anatomical, physiological, and neuromuscular mechanisms that are suggested to
contribute to the ACL dilemma. Once these important factors have been identified, the
creation of abatement programs may become valuable tools that may help stem the

increasing incidence of ACL injury.

Function of the ACL

Stability of the human knee joint is chiefly provided by the collateral ligaments on
the medial (tibial collateral) and lateral (fibular collateral) sides of the joint, and the
anterior and posterior cruciate ligaments (Figures 1 and 2) within the joint capsule. In
addition to these ligaments that bind the bones of the joint together, there are various
muscular, tendinous, and ligamentous expansions that also help to stabilize the joint.
Muscle in particular plays a protective role in joint stabilization by 1) strain relief of the
ligaments and 2) impact absorption of the loads transmitted through the lower extremity
(Withrow, Huston, Wojtys, & Ashton-Miller, 2006; Wojtys & Huston, 2000). The
complex arrangement of these tissues with respect to the skeletal structure of the knee
joint is reviewed and described in detail by Aiello and Dean (1999).

The ACL arises from the anterior intercondylar space on the tibial plateau, runs
upwards and posteriorly, and attaches on the inside of the lateral condyle Of the femur.
This ligament becomes taut as the knee joint extends and chiefly prevents the femur from
sliding posteriorly off the tibial plateau (Wojtys & Huston, 2000; Aeillo & Dean, 1999;

MacWilliams, Wilson, DesJardinS, Romero, & Chao, 1999). The posterior cruciate

21

ligament (PCL) arises from back on the intercondylar space of the tibial plateau, runs
upward and anteriorly, and attaches on the inside of the medial femoral condyle. The
PCL becomes taut as the knee joint is flexed and thus prevents the tibia fiom sliding
anteriorly off the tibial plateau (Aeillo & Dean, 1999).

Another chief function of the cruciates is to limit medial rotation of the tibia in
relation to the femur. With medial rotation of the tibia with respect to the femur, the
cruciates twist around each other to aid in preventing further rotation. However, in lateral

rotation, they untwist and have no limiting ability (Aeillo & Dean, 1999).

22

 
  
  
 
   
 

Famur
Lateral Collateral Ligament

Posterior
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Figure I. Anterior view of the right knee joint.

 

lRetrieved August 31“, 2005 fi'om the World Wide Web: http://www.steadman-

hawkins.com/virtual/education/acl.htrnl

23

 

 

 

 

Posterior

PCL

MCL

   

Medial
Meniscus

Lateral
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Figure 2. Superior view of the right knee joint.

 

2Retrieved August 31“, 2005 from the World Wide Web: http://www.arthroscopy.com/sp05001.htm

24

Mechanism of Injury

Efforts to identify the special circumstances with which ACL injuries occur
among female athletes indicate the majority of incidents are typically non-contact in
nature, occurring while the athlete is landing from a jump or conducting a pivoting or
sidestep cutting-type maneuver (McClean et al., 1999). Hewett (2000) has reported that
approximately 80% of all ACL injuries occur via non-contact mechanism after landing
from a jump. Investigations utilizing retrospective injury data have further described this
injury mechanism as involving an external tibial rotation in relation to an internal femoral
rotation (Figure 3), coincident with a valgus stress at relatively low knee flexion angles,
while suddenly decelerating on a fixed or planted foot (Dorizas & Stanitski, 2003;
Kirkendall & Garrett, 2000; Hewett, 2000; Rosene et al., 1999; Wilk et al., 1999; Delfico
& Garrett, 1998; Cross, Gibbs, & Bryant, 1989).

Ireland (1999) has labeled one particular state of femoral anteversion, external
tibial rotation, and concurrent foot pronation as the “position of no return” (Figure 4),
while others have Simply referred to this circumstance as “miserable-mal-alignment”
(Fulkerson & Arendt, 2000). Chappell et a1. (2002) have indicated that landing from a
jump in concert with enhanced extension and valgus moments at the knee and
deceleration of the body, is conducive to producing an anterior Shear force at the
proximal tibia that contributes to an anterior tibial translation with respect to the femur
(Figure 5). It is believed that this anterior tibial “drawer” effect places the ACL ligament
in a vulnerable position upon landing or cutting and exacerbates the conditions through

which partial or complete mechanical failure of the ACL is accomplished.

25

 

Figure 3. External tibial rotation at the right knee relative to the femur.

 

3Retrieved August 31", 2005 from the World Wide Web: http://www.hughston.com/hhafb_l1_3_2b.jpg

26

J _‘_ Excessive Knee
fl Valgus Disposition

 

Normal Neutral . , L."
F00t : ;. Pronated Foot

5.!

Figure 4. Normal neutral position (A) and the “Position of no return” exhibiting

excessive femoral anteversion, external tibial rotation, and concurrent foot pronation (B).

 

4Retrieved September 15‘, 2005 from the World Wide Web: http://www.algeos.com/biomechanics.htm

27

Femur

Anterior ,
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Meniscus

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,
n
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9 x
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.

Figure 5. Anterior tibial drawer effect enhances the conditions for partial or complete

mechanical failure of the anterior cruciate ligament.

 

5Retrieved September 1”, 2005 from the World Wide Web: http://www.greatpyrrescue.org/

newsletter/aug_03/ fig2.jpg

28

To further understand these proposed injury mechanisms, it becomes important to
identify and observe those potential movements and anatomical, physiological, and
environmental factors that are evident when ACL injuries occur. Identifying the
conditions that predispose female athletes to ACL injury may assist future investigators
and practitioners in the design and implementation of definitive intervention strategies to

mitigate the frequency and severity of this type of injury.

Intrinsic and Extrinsic Factors Associated with ACL Injury

Cultural sociologists often consider sport and recreation to be important and vital
markers of a growing and thriving culture. Evidence of this phenomenon within the
United States is clearly observed by the increasing number of participants that engage in
both individual recreational activities and team sports (Huston et al., 2000; McClean et
al., 1999). Women, men, and children from a variety of socio—economic backgrounds
and levels of individual ability are provided with numerous opportunities to participate in
competitive recreational leagues, fitness clubs, community centers, and activity groups.

Associated with an increase in the number of active Sport and recreational
enthusiasts is a concomitant increase in the number of injuries that result from
participation. These injuries occur under a variety of environmental conditions, game
circumstances, and etiological factors such as experience, coaching, supervision, playing
surface, equipment, and human factors. These variables are typically referred to as
“intrinsic” or “extrinsic” factors (Hewett et al., 2006; Huston, et al., 2000).

Intrinsic factors are those factors that include intra-individual characteristics such
as growth, maturation, lower-extremity alignment, muscular strength, joint mobility, joint

laxity, and hormonal factors. Intrinsic factors are typically difficult to control and may

29

not be modifiable (Harmon & Ireland, 2000). Unlike intrinsic factors, extrinsic factors
may be modifiable and include such areas as neuromuscular proficiency, individual
motor competence (dexterity), musculoskeletal agonist-antagonist joint-strength ratios,
supervision and instruction, playing surface, level Of competition, and equipment (Huston
et al., 2000).

Although it is generally understood that these intrinsic and extrinsic factors are
interdependent, the interactions between physical environment, learning, coaching,
physical structure, and the endocrine system are sensitive, unavoidable, and influential on
human neuromuscular synergy and ligamentous integrity (Fulkerson & Arendt, 2000;
Harmon & Ireland, 2000; Hewett, 2000; Hosea et al., 2000). To further elaborate how
these interactions occur, it is necessary to define those special intrinsic and extrinsic
factors believed to play a vital role in ACL injury.

Intrinsic Factors

The principle intrinsic factors that have garnered the most attention in the
literature concerning ACL injury are skeletal dimorphism and the influence of the
endocrine system. Although dimorphism can be misconstrued as a “mal-alignment” of
the Skeletal structures, it represents that predisposition defined by sex and through the
process of normal growth and maturation that distinctly allows the female skeleton to “re-

design” itself in preparation for child-bearing (Aiello & Dean, 1999).

Anatomical Factors

Lower extremity skeletal dimorphism provides anatomical configurations that are
believed to contribute to the disparity in the incidence of knee injury among female and

male athletes (Huston et al., 2000; Fulkerson & Arendt, 2000; Harmon & Ireland, 2000;

30

Heiderscheit et al., 1999; Neely, 1998; Hvid & Andersen, 1982). However, because there
is practically little one can do to alter the process of Skeletal dimorphism, intervention
with respect to this problem does not present practical solutions for reducing the
incidence of ACL injuries among females. Despite the inability to effectively provide
practical interventions that can affect the process of skeletal dimorphism, the knowledge
and understanding of those skeletal structures, believed to contribute to the primary ACL
injury mechanism, is valuable and may provide insight into designing potential

intervention protocols that may minimize the ACL injury dilemma.

Because the pelves, femur, and tibia are anatomically and kinetically linked with
respect to lower extremity locomotion in activities such as walking, running, jumping,
and hopping, these skeletal structures have garnered frequent analysis in research and
clinical settings. Typically, the target of these research projects has involved the
quadriceps angle (Q-angle), femoral anteversion, and the intercondylar notch of the
femur.

Q-angle. The Q-angle is defined as the acute angle between the line connecting
the anterior suprailiac spine (A818) and the midpoint of the patella, and the line
connecting the tibial tuberosity with that same patellar reference point (Figure 6).
Various studies have determined the average Q-angle for men and women to range from
approximately 8 to 20 degrees, with women having consistently greater Q-angles than
men (Huston et al., 2000) . This disparity in measurement is typically attributed to the
broader pelves and shorter femurs, more prevalent to the adult female when compared to

the adult male (Huston et al., 2000; Neely, 1998).

31

This Q-angle difference is widely considered the chief contributor for excessive
femoral anteversion, genu-valgum (knock-knees), and a resulting external tibial torsion in
the female athlete (Neely, 1998). As a result of these three skeletal expressions, there
exists the potential to produce greater mechanical stress upon the musculo-tendinous,
ligamentous, and articular structures of the lower extremities (Heiderscheit, Hammil, &
Van Emmerik, 1998). Thus, the associated mechanical distribution of loading forces on
articular structures may eventually lead to abnormal patello-femoral tracking, which may
in turn lead to abnormal mechanical compressive, shear, and torsional stresses applied
over a smaller joint surface area (Neely, 1998).

The potential exists for these articular structures to be ill prepared for this type of
irregular loading, thus pathological conditions such as patello-femoral distress syndrome
and chondomalacia may become precursors to ACL and medial collateral ligament
(MCL) failure. Chondromalacia is a gradual degeneration of articular cartilage that may
play a role in altering walking gait, running gait, and, most important for some sports, the
ability to change direction in a mechanically efficient manner under unpredictable
circumstances (Heiderscheit, et al., 1999; Huberti & Caves, 1984; Hvid & Andersen,
1982).

Although the magnitude of the Q-angle measure is recognized as generally greater
in the adult female when compared to the adult male, there exists strong doubt as to
whether there is a positive relationship between Q-angle and knee injury. Several
investigations have indicated that the magnitude of the female Q-angle as not significant

when normalizing with respect to femoral length (Huston et al., 2000). In addition, it is

32

Anterior
superior iliac
spine

 

Acetabulum

Figure 6. Q-angle.

 

6Retrieved September 1", 2005 from the World Wide Web: http://www.steadman-hawkins.com

/virtual/education/assets/cLangle.gif

33

typically emphasized that there are a significant number of female athletic participants
that possess high range Q-angle values with no reported lower extremity abnormalities
(Hewett, 2000).

An additional problem associated with these measures is the reported unreliability
of the various techniques utilized to assess the Q-angle among female and male
populations. Nester and France (2001 ), upon evaluating several reported studies
concerning the measurement of the Q-angle, reported extreme variability with respect to
the standard deviations of Q-angle measurements due to errors in marker placement on
the subjects. Neely (1998) has also found variability in measurement technique leading
to poor reliability with regard to Q-angle measures, making it increasingly difficult to
derive definite conclusions. Thus, these findings enhance the difficulty with which
investigators can relate ACL injury pathology on the basis of Q—angle measurement
alone.

Femoral Anteversion. Femoral anteversion is an anatomical condition where the
femoral head and neck are rotated anterior to an imaginary line directed through the
femoral condyles in the horizontal plane (Figure 7). Average reported values for both
males and females are typically in the range of 8 to 18 degrees, with female values on
average typically higher when compared to males (Neely, 1998).

Femoral anteversion is considered a precursor to excessive internal rotation at the
hip, and is believed to be established through the broadening of the pelvic bones with
maturation, resulting with an enhanced Q-angle with greater potential for placing the
respective acetabulum (Figure 6) in an anteriorly directed disposition (Neely, 1998; Hvid

& Andersen, 1982). Because femoral anteversion restricts external rotation about the hip,

34

the Q-angle has the potential to be enhanced, thus potentially creating a compensatory
increase in external tibial torsion, excessive pronation of the feet, and a greater val gus
(knock-kneed disposition) effect with weight-bearing. These structural compensations
for femoral anteversion are considered optimal because they minimize energy
expenditure, via the anteriorly rotating femur and the externally rotated tibia, during
locomotion such as walking or running (Fulkerson & Arendt, 2000).

Clinical studies have reported excessive pronation of the foot when the lower
extremities are placed into this valgus condition. Excessive pronation is associated with
several overuse syndromes, including patello-femoral distress and Chondromalacia.
These syndromes are typically the result of abnormal mechanical applications of force
throughout the patello-femoral and patello-tibial articular structures (Heiderscheit, et al.,
1999; Huberti & Caves, 1984; Hvid & Andersen, 1982).

Although femoral anteversion has been linked to lower extremity dysfunction, its
role as a primary determinant in non-contact ACL injury is inconclusive. Researchers
have been unable to link the reported range of values with acute or chronic knee injuries,
particularly because of the evidence that injuries are not necessarily manifested in those
with excessive femoral anteversion values (Neely, 1998).

Further difficulty arises when anteversion ranges are associated with an increase
in Q-angle value or vice versa. Reports of poor reliability of measured values and highly
inaccurate methods of measuring both femoral anteversion and Q-angle have made the
association of femoral anteversion as a direct determinant of ACL injury difficult to

surmise (Nester, 2001; Neely, 1998).

35

 

 

 

Figure 7. View of the right femur showing femoral anteversion.

 

7Retrieved September 1“, 2005 from the World Wide Web: http://www.hopkinsmedicine.org/

orthopedicsurgery/images/fem_ant.png

36

Intercondylar Notch Width. Through the use of radiograph a notch width index
(NW 1), which is a ratio that is determined by comparing the width of the femoral
intercondylar notch to the distance between the two distal femoral condyles at the level of
the popliteal groove (Figure 8). Several investigations have suggested that there are
pathologic relationships among small NW1 values (e. g., patello-femoral distress, and
acute ACL injury among female athletes), while other investigations have yielded little
association between a small NW1 measure and ACL injury (Huston et al., 2000; Harmon

& Ireland, 2000; Arendt & Dick, 1995).

Much of the association between narrow intercondylar notches and ACL injury
stems from the hypothesis that a narrow intercondylar notch is reflective of an ACL that
is smaller in diameter with greater risk of mechanical failure versus larger diameter
ligaments. Interestingly, notches typically assume an “H”, “C”, or “A” notch shape with
the “A” notch obtaining the narrowest measures (Figure 9). Narrow notches structurally
imply a congenitally smaller ACL, which may be more susceptible to chronic and acute
stress damage (Huston et al., 2000; Harmon & Ireland, 2000).

Another disadvantage of a smaller ACL ligament is risk of intercondylar
impingement. Several studies utilizing cadaver specimens indicate that, during knee joint
flexion, it is apparent the ACL will come in contact with the medial margin of the lateral
femoral condyle. During extension movements, the ACL may impinge on the anterior
intercondylar notch (Neely, 1998).

Despite these findings, attempts to link notch shape and ACL ligament diameter
have proven to be inconclusive because many athletes with small NWI’s compete at a

high level of competition with no history of chronic knee discomfort or acute knee injury

37

(Neely, 1998). Due to the large range of NW1 measures that exist within sexes and the
considerable overlap in NWI between genders, many investigators argue it is difficult to
conclude that ACL injury is principally derived from this anatomical factor. In addition,
there is need to standardize NWI measurements since many of these research
investigations have utilized a variety of techniques (i.e., computed tomography,
radiographs) at a variety of knee flexion angles to produce conclusions with respect to
NWI and notch shape (Arendt & Dick, 1995). The inability to conclude that
intercondylar NWI and notch shape are instrumental in ACL ligament failure suggests
that it is an anatomical feature that warrants further investigation (Harmon & Ireland,
2000; Hvid & Anderson, 1982).

Summary of Anatomical Factors

The contradictory nature of many studies and a lack of conclusive evidence lend
uncertainty to whether or not the lower extremity skeletal structures are a direct
mechanism for ACL ligament failure. However, the associations of these intrinsic
conditions for both chronic and acute knee injury indicate that these anatomical factors
may operate in conjunction with other potential intrinsic and/or extrinsic factors (Hewett
et al., 2006; Hewett, 2000; Demont et al., 1999). In spite of this conclusion, there are no
practical or non-invasive interventions currently available that could alter normal lower
extremity skeletal grth and development. The lack of potential solutions regarding
anatomical differences and their contributions to serious knee pathology demonstrate the
need to further explore the potential influence of other intrinsic and extrinsic mechanisms

that appear to operate in combination with lower extremity alignment.

38

 

 

 

-" :\‘~. ;' A = “faith of the femoral
‘ . intercondylar groove.
I -... .4. _ B = Distance between the
, / '. , two femoral condyles at
‘. : , the level of the popliteal
Popllteal Groove ,T‘ ~ .. groove.
‘ 7‘ 1 #‘w
i A , . ' NWI . AIB
a ,'

Figure 8. Notch width index (NW 1).

 

8Retrieved September 2““, 2005 from the World Wide Web: http://orthoinfo.aaos.org/fact/thr_report.

cfm?thread_id=l 57&topcategory=Knee

39

 

 

Figure 9. Intercondylar notch shapes.

 

8Retrieved September 2nd, 2005 from the World Wide Web: http://orthoinfoaaos.orgfact/thrjeport.

cfm? thread_id=l 57&topcategory=Knee

4O

Hormonal Factors

The menstrual cycle is a physio-endocrine event unique to females with hormonal
circulation regulated via the coordinated functioning triad of the hypothalamus, pituitary
gland, and ovaries. The duration of the average menstrual cycle is approximately 28
days, but is reported to be quite variable with cycles as short as 20 days and as lengthy as
45 days (Wojtys, Huston, Lindenfield, Hewett, & Greenfield, 1998).

Changes in the female sex steroids that modulate the endocrine events during the
menstrual cycle are typically divided into phases that also exhibit variability in time
[follicular phase (days 1 to 9), adulatory phase (days 10 to 14), and lacteal phase (days 15
to end of the cycle)]. During the follicular phase, concentrations of both estrogen and
progesterone are relatively low. As the cycle progresses toward the adulatory phase, it is
preceded by a large surge in estrogen. The lacteal phase follows ovulation with
significant increases in both estrogen and progesterone, and then significantly tapers in
concentration to the start of the following cycle (F rankovich & Labrum, 2000; Heitz et
al,l999)

Through a variety of endocrinal mechanisms, sex hormones indirectly affect the
active and passive stabilization properties of the female musculoskeletal system, notably
due to the presence of estrogen and progesterone receptors located in the synoviocytes
within the synovial lining of the knee, fibroblasts in the stroma, and cells in the blood
vessel walls of the ACL of women (Frankovich & Lebrun, 2000). Sex hormones also
play an inhibitory role in fibroblast proliferation and collagen formation, and it is
believed that fluctuations in concentration of these sex hormones alter the metabolism of

cells in the ACL and in turn influence ligament structure, composition, and integrity (Y u,

41

Panossian, Hatch, Liu, & F inerrnan, 2001; Huston et al., 2000; Frankovich & Lebrun,
2000; Hewett, 2000; Harmon & Ireland, 2000; Wojtys et al., 1998).

Estrogen has been shown to have measurable effects on the female neuromuscular
system with significant changes in contracting and relaxing properties of skeletal muscle,
tendon, and ligament strength (Hewett, 2000). Utilizing a knee arthrometer during
periods of peak hormonal surges, Heitz et a1. (1999) found significant differences in ACL
laxity during the follicular and luteal phases of the menstrual cycle, especially through
days 10 to 13 of the ovulatory phase. Because the ACL operates in combination with
various muscles that cross the knee joint in providing stability, a ligament that exhibits
greater laxity will lend less support to the joint and introduce proprioceptive challenges,
particularly while undergoing rapid dynamic loading as evidenced during various lower
extremity sport actions (Hewett, 2000; Rozzi, Lephart, Gear, & Fu, 1999).

Arendt and Dick (1999) in a review of studies documenting ACL injury
occurrence and menstrual cycle activity have found a greater incidence of ACL injury to
occur significantly before or after the ovulatory phase of the menstrual cycle. Despite
these findings, determining a consistent phase with which ACL injury can be associated
has proven to be difficult. In one prospective study over a three-year period, 27 female
athletes self-reported within 72 hours the days of their menstrual cycle and provided
samples for sex-hormone determination after sustaining an ACL injury. Results of the
study concluded 10 of the 27 athletes incurred injury at day one or two of the follicular
phase (Slauterbeck, Fuzie, Smith, Clark, Xu, Starch, & Hardy, 2002). In contrast, Wojtys

et a1. (1998) in a retrospective study utilizing 28 subjects with acute ACL injury over a

42

three month period, found a significant association (29% of all ACL injuries) between
ACL injury and the ovulatory phase of the menstrual cycle.

Wojtys et a1. (2002) conducted another prospective study with 65 participants
over two years in which hormonal assays were conducted within 24 hours of injury and a
second assay was conducted within 24 hours of the first day of the menstrual cycle.
F orty-three percent or 28 of the 65 subjects incurred an ACL injury during the ovulatory
phase while there were 15 and 22 ACL injuries during the follicular and luteal phases,
respectively. Although not considered an exclusionary criterion, oral contraceptive use
by the participants was also documented for this study. Interestingly, those not taking
oral contraceptives were more likely to injure the ACL during the ovulatory phase (N =
24) than during the follicular or luteal phases of the menstrual cycle. Eight of the 14
subjects that utilized oral contraceptives incurred injury during the follicular phase of the
menstrual cycle, but no significant effects were discussed with respect to the study.
Additionally, the number of subjects utilizing oral contraceptives was relatively low

(N=14) and suggests this is a factor that warrants further investigation.

Summary of Hormonal Factors

In light of the suggested indirect association between hormonal mechanisms and
ACL injury, studies in this area appear to be inconsistent in defining a specific
relationship between ACL injury occurrence and a specific phase of the menstrual cycle.
Much of this difficulty stems from the determination of specific serum hormone levels
that are considered the definitive gold standard in establishing cycle phase. Inconsistent
definitions in menstrual cycle phases contribute to the discrepancies in the findings.

Wide circadian variation in hormonal secretion among normal women and discrepancies

43

in the timing of testing also contribute to conflicting results, particularly when a variety
of testing methods have been employed (Wojtys, etal., 2002; Frankovich & Lebrun,
2000)

Since hormone stabilization via oral contraception has been implicated as a viable
method of altering the tensile properties of the ACL, thus a preventative intervention, it is
a proposition that should be further investigated. More research is needed with respect to
sample size power, type of contraceptive, chronological age, and factors associated with

normal physical grth and maturation.

Extrinsic Factors

Unlike intrinsic factors that are associated with the inherent anatomical and
physiological characteristics of an individual, extrinsic factors are related to potentially
modifiable traits associated with the type of sport, environmental conditions of the
activity, physical conditioning of the athlete, and equipment used (Harmon & Ireland,
2000). Examples of extrinsic factors include neuromuscular proficiency, individual
motor competence, musculoskeletal agonist-antagonist joint-strength ratios, quality of
supervision and instruction, playing surface, level of competition, and equipment (Hewett
et al., 2006; Huston et al., 2000; Harmon & Ireland, 2000).

Because extrinsic factors have the potential to be modified, efforts to address the
issue of ACL injury and the gender bias from this perspective are being aggressively
pursued in attempting to understand how these factors relate to injury, and, if so, how and
when can modification be implemented to attenuate the rate of injuries. Adding further
to the dilemma of determining how to intervene is the difficulty of objectively measuring

parameters of these extrinsic factors in order to be both appropriate and effective.

44

Although tangible in concept, instruction can be delivered in a variety of mediums
and generate circumstances with varying outcomes. In addition, inadequate financial
resources, poor facility maintenance, or a lack of institutional foresight can contribute to
the manifestation of playing conditions that are less than desirable or equipment that is
aged and inferior in design. The ability to quantify terms like “fimctional” or “safe” is
difficult and often intangible for the injury epidemiologist attempting to control for these
abstract concepts while conducting scientific research. As a result, extrinsic factors
associated with neuromuscular control represent that area frequently addressed in the

investigative literature concerning ACL injury patterns among female athletes.

Muscle Strength and Recruitment

Understanding sex differences and their role in neuromuscular function with
respect to the dynamic motion and stabilization of the knee joint appear to be the most
rational factors to explain the different rates of ACL injury between males and females
(Schultz, Perrin, Adams, Arnold, Gansneder, & Granata, 2001). In concert with this
paradigm, there appears to be compelling support for the position that the development of
neuromuscular control strategies are essential in providing dynamic joint stability and
protection while performing athletic tasks (Withrow et al., 2006; Hewett et al., 2006;
Rodacki, Fowler, & Bennett, 2002; Lloyd & Buchanon, 2001; Schultz & Perrin, 1999;
Rozzi, et al., 1999; Rosene & Fogarty, 1999; Huston & Wojtys, 1996).

Previous investigations have examined quadricep and hamstring strength to
determine if significant differences exist between males and females and further, to
determine if significant agonist-antagonist muscular strength discrepancies introduce a

predisposing risk for ACL injury. In general, these investigations have concluded that

45

women produce significantly less muscle force in both the quadriceps and hamstrings,
even when normalized for body mass (Lephart, Ferris, Riemann, Myers, & Fu, 2002;
Huston et al., 2000; Harmon & Ireland, 2000; Huston & Wojtys, 1996).

Because the quadriceps and harnstrings are the dominant musculature surrounding
the knee, the strength of these muscles add to the dynamic component of joint stability,
thus equalizing articular surface pressure distribution and regulating mechanical
complexion (Withrow etal., 2006; Huston et al., 2000). Taking into consideration
inadequate muscular strength, weaker musculature may not be able to provide the
protective defense necessary to maintain joint integrity and alleviate potentially damaging
mechanical loads on the li gamentous structures of the knee under dynamic conditions.

Knee Joint Kinematics and Ground Reaction Forces

Utilizing various kinematic and kinetic data collection techniques, several
investigations have provided strong evidence that neuromuscular control of the knee joint
while landing from a jump or performing a cutting maneuver on a rigid surface can be
appraised through the interpretation of biomechanical variables. As a result, congruent
relationships have been established and measured, in particular: angles of knee flexion at
impact; time to peak flexion on impact; knee varus, valgus, extension, and flexion
moments; peak ground reaction forces; time to peak ground reaction force; and activity of
the various musculature of the knee through EMG analyses (Sell, Ferris, Abt, Tsai,
Myers, Fu, & Lephart, 2006; Hass, Schick, Chow, Tillman, Brunt, & Cauraugh, 2003;
Lephart, Ferris, Riemann, Myers, & Fu, 2002; Besier et al., 2001; McNitt-Gray, Hester,

Mathiyakom, & Munkasky, 2001; Colby et al., 2000; McClay, Robinson, Andriacchi,

46

Frederick, Gross, Martin, Valiant, Williams, & Cavanagh, 1994; Devita & Skelly, 1992;
Dufek & Bates, 1991; Cross et al., 1989).

Because variant landing and cutting movements are inherent characteristics in
many sports, the concomitant effects of ground reaction force (GRF) and measures of
knee joint flexion on impact have been implicated as potentially defining the relationship
between these contact forces and lower extremity injury (Malinzak, et al., 2001; McClay
et al., 1994; DeVita & Skelly, 1992; Dufek & Bates, 1991). In particular, because low
angular ranges of knee flexion may induce greater contribution of the quadriceps in
producing anterior tibial shear forces, the loads placed on the ACL may be greater and
manifest conditions conducive to producing traumatic injury (Withrow et al., 2006;
Chappel et al., 2002; An, 2002; Malinzak et al., 2001; Hewett, 2000).

Several investigations have examined knee joint flexion in subjects on impact
after landing and cutting to determine relationships between ground contact force and
knee flexion. Colby et a1. (2000), in a study designed to evaluate the range of knee
flexion in subjects during foot strike and subsequent performance of various cutting
tasks, obtained a range of values from 14 degrees (stopping) to 29 degrees (cross-cut) of
flexion for subjects of both genders. Although no ground reaction force data were
collected, the study exhibited the kinematic variability associated with different motor
tasks, in this case, cutting maneuvers. As a result, efforts are typically directed toward
reinforcing the value of developing biomechanical response strategies under a variety of
conditions to help dissipate potentially injurious landing forces (James, Bates, & Dufek,

2003; Hewett, 2001 ).

47

Interestingly, the association among ground reaction forces and the range of
angles of knee flexion on impact are not always clearly defined. McClean, Lipfert, and
Van Den Bogert (2004), in an investigation of intercollegiate males and females
performing a sidestep-cutting maneuver, implemented the use of a defensive player or no
defensive player to introduce a variable condition and determine the influence of this
scenario on various biomechanical parameters of the knee joint. With the defensive
player condition, participants demonstrated enhanced ground reaction forces with
decreased knee joint flexion on impact, a finding that is in contrast to previous
investigations (Malinzak, et al., 2001; McClay et al., 1994; DeVita & Skelly, 1992).

In a previous investigation, McLean et a1. (1999) compared knee kinematics
among high-level intercollegiate males and females performing a running and cutting
task. The investigators did not find significant differences with respect to maximum knee
flexion, but did find that maximum flexion in the stance phase, while cutting, occurred
significantly later among the males.

Elkhart et al. (2002), in a jump study comparing intercollegiate female athletes to
recreational male athletes, found the female athletes to exhibit significantly less mean
knee flexion displacement (-17.4l ° i 12.96°) than the male controls (-31.10° 2*: 92°),
while sustaining ground reaction forces that were not significantly different for both
single and double leg landings. In addition to recording the flexion and impact values,
time to maximum angular displacement was also determined. The female athletes

demonstrated less time to maximum knee flexion (130.04ms i 71 .8ms) when compared

to their male counterparts (187.0ms i 43.98ms). Despite the greater mass values for the

48

male participants (+7.45kg), males appeared to utilize greater flexion at the knee and
more time to peak flexion to attenuate the ground contact forces.

In a similar study by Dagenham and Darling (2003), intercollegiate female
athletes demonstrated 10 to 14 degrees greater knee flexion and greater knee flexion
accelerations than their male counterparts on landing from a maximal height jump under
non-fatigued and fatigued conditions. One limitation to this study is the difficulty in
ascertaining whether the increased flexion angles and increased knee flexion
accelerations are an indicator of the relative strength of the individual or a compensatory
motor strategy.

Although ground reaction force data was not collected for the Fagenbaum and
Darling study (2003), Bates and Dufek (1991), have expressed that the height of jump
plays a minor role with respect to GRF’s in comparison to knee joint angle at touchdown
and the knee joint flexion angle can be used to reduce the magnitude of impact loads
while landing. Thus, it would appear that perhaps the female athletes in the F agenbaum
and Darling (2003) study may have implemented a greater flexion strategy to compensate
for other neuromuscular factors that potentially contribute to ACL injury (e. g., latent
quadricep-hamstring firing, valgus predisposition).

DeVita and Skelly (1992), studying eight female intercollegiate volleyball and
basketball players landing under both soft and stiff conditions, compared ground reaction
forces, joint positions, joint moments, and muscle power in the lower extremities. Soft
landings averaged 117 degrees of knee flexion versus 77 degrees in the stiff landing, and
the mean floor contact phase time (from initial contact until maximum knee flexion) for

the female was 152ms versus 342ms for males. During the stiff landings, larger hip and

49

knee extensor moments were observed in addition to larger ground reaction forces, thus
demonstrating the knee musculature likely absorbed more energy over time under the soft
landing conditions, versus a relatively large force application over a shorter period of
time under the stiff conditions.

In concert with the jump investigations of F agenbaum and Darling (2003), DeVita
and Skelly (1992), Bates and Dufek (1991), and Sell et a1. (2005) provided evidence that
type of jump may play a critical role in defining the magnitude of various biomechanical
parameters about the knee. Using multi-directional stop-jump tasks and a vertical jump
under reactive conditions, the investigation yielded significant increases in ground
reaction force and decreased knee joint flexion on impact, particularly during lateral stop-
jump tasks on the side of non-dominant leg and vertical jump. The authors implied the
stop-jump task to the non-dominant side required participants to perform a movement
that assimilates a side-step cutting maneuver and predisposed them to the “position of no
return” as described by Ireland (1999).

Muscles exhibit lengthening which oppose joint flexion during landing and this is
reflected as a net joint extensor moment indicative of the muscles role as a shock
absorber. Because extensible properties of muscle allow the tissue to absorb much of the
impact associated with landing from a jump, flexion on impact is an indicator that force
attenuation is taking place (McClay et al., 1994; Devita & Skelly, 1992; Dufek & Bates,
1991). These findings, in concert with those of Lephart et al. (2002) and Malinzak et a1.
(2001), appear to suggest that the ability to attenuate ground reaction forces on landing
fiom a jump or when performing a cutting maneuver may indeed be associated with

neuromuscular capability to devise an appropriate landing strategy. Although stiff

50

landing techniques afford the performer the opportunity to move faster or quickly after
initial ground contact, this may occur at the expense of producing potentially greater joint
moments and power values which concomitantly can be associated with a greater risk for
injury (DeVita & Skelly, 1992).

Knee Joint Extensor Moments

Muscles have a flexion moment arm if they can support/resist an extension knee
moment and an extension moment arm if they can support/resist a flexion knee moment
(Lloyd & Buchanon, 2001; Hewett, Stroupe, Nance, & Noyes, 1996). Because the
muscles of the quadriceps and the hamstrings represent that anatomical constituent
responsible for generating moments associated with knee joint stabilization while landing
from a jump, the assessment of the flexion and extension moments provide an
opportunity to gain insight into the potential for serious ACL injury.

Several investigations have identified net joint extension moments acting
eccentrically to oppose knee joint flexion in order to absorb the kinetic energy associated
with landing tasks (Chappel et al., 2002; McClay, 1994; DeVita & Skelly, 1992).
Chappell et a1. (2002), comparing women recreational athletes to male recreational
athletes, found women (60.0 i 5.9kg) to exhibit greater knee extension and valgus
moments than the men (76.6 :t 9.5kg) during a three-step jump-stop task for maximal
vertical height. Although the values were not significant, the results indicate women may
use alternate motor control strategies during landing tasks. In conjunction with these
findings, the authors indicated the peak extensor moments were associated and

synchronized with peak proximal anterior shear forces at the knee, likely due to

51

decreased angles of knee flexion, increased quadriceps activity, decreased hamstring
activity, or a combination of all three conditions.

These conditions are in concert with the findings of Malinzak et al. (2001) who
demonstrated intercollegiate recreational female athletes exhibit decreased knee flexion
angles on landing, increased muscle quadriceps activation, and decreased hamstrings
muscle activation when compared to their male counterparts. Interestingly, these
differences may be exacerbated under unstable or unpredictable circumstances such as
those typically exhibited under conditions of athletic competition.

These investigations appear to support the proposition that males may employ
different neuromuscular mechanisms to compensate for high landing forces than those
used by female athletes, especially with respect to the effective balance of opposing joint
torques. As a result, mitigating the common occurrence of these events may be an
important tool in reducing potential knee injury risk factors since they are characteristics
that are pronounced in studies examining ACL injury etiology of the female athlete
(Kirkendall & Garrett, 2000; Hewett, 2000; Rosene et al., 1999; Wilk, et al., 1999;
Delfico & Garrett, 1998; Cross et al., 1989).

McClay et al. (1994) expressed that there is further concern generated during stiff
landings and those jumps that possess greater vertical displacement because of the
potential for higher associated extensor joint moments and ground reaction forces that
may enhance the intensity and duration of stress to the structures of the knee joint. In a
study examining knee joint kinetics associated with landing from a vertical jump, Devita
and Skelly (1992) suggested the knee joint extensor moment acts to support the body’s

center of mass on impact rather than reduce the downward velocity. Thus, the

52

 

 

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implication of this action may influence the relationship between ground reaction forces
and the knee joint extensor moments, and suggests changes or alterations to the knee joint
extensor parameter may modify or attenuate associated ground reactions forces and be

important to identify with regard to landing activities.

Summary of the Extrinsic Factors

Upon conducting a review of the pertinent literature, there is compelling evidence
to suggest that extrinsic factors are greatly influenced by the neuromuscular control
exhibited on the muscles surrounding the knee joint. Because the female athlete appears
to demonstrate a more latent response for agonist-antagonist co-contraction, greater
extension moment values on.impact, less knee joint flexion on impact, and faster times to
peak flexion when landing from a jump or performing a cutting maneuver, these
measures enhance the potential for higher associated peak GRF’s and thus, the potential
for serious ACL injury (Hewett, 2000; Hewett et al., 1996; Dufek & Bates, 1991).

Devita and Skelly (1992) have emphasized that in order for muscle to effectively
contribute in the dissipation of kinetic energy, it requires not only greater angles of
flexion on impact, but more time to peak flexion. Lephart et a1. (2001) concurred with
this position in supporting the notion that peak flexion angle on impact and time to peak
flexion angle become valuable indicators of the ability to attenuate GRF’s from a landing
or cutting maneuver.

The muscles and ligaments surrounding the knee control how the total joint force
is shared between the articular surfaces of the femur and the tibia, and it is recognized
that the ligaments of the knee become more taut when the knee is in more extended

postures. Because of the ACL’s role in restraining anterior tibial translation, poor

53

 

 

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neuromuscular synchronization between the secure compression effects of
quadricep/hamstring co-contraction can create an environment of decreased functional
knee joint stability and open to potential ACL injury when landing from a jump or
conducting a cutting maneuver. There is further concern when the temporal
characteristics of the peak forces are occurring earlier, rather than later in landing,
indicating potentially dangerous forces need to be managed throughout the cycle of
landing and/or cutting (Dufek & Bates, 1991). Upon reviewing the literature, men appear
to be spending a greater percentage of stance time eccentrically loading the quadriceps,
thus, perhaps spending more time controlling and stabilizing knee joint motion before the
generation of axial torques, when compared to women (McLean et al., 1999).

Interestingly, males experience higher impact forces from landing, yet suffer
fewer injtuies. This may indeed be related to their ability to decrease the extension,
adduction, and abduction moments when making impact with the ground surface. Thus,
the ability to coordinate proper landing strategies in order to initiate protective
neuromuscular defense mechanisms that provide functional joint stability under dynamic
conditions appears to be an effective protocol for the male athlete to reduce the potential
for risk of serious knee injury (Huston et al., 2000).

Collectively from a research perspective, it is apparent that efforts to initiate
changes of the neuromuscular parameters among female athletes must begin with
understanding how the nervous system controls muscular dynamics in devising
compensatory strategies to help attenuate those GRF’s and neuro-mechanical

characteristics that may contribute to the ACL injury dilemma.

54

Functional Joint Stability, Muscle Stifiness, and Kinesthesia

Although motor control is an area of study that is exhaustively scrutinized, there
exists a great body of information that remains both inconclusive and elusive with respect
to how the central nervous system (CNS) specifically dictates normal limb firnction and
locomotion. Despite these shortcomings, essential tenets of neurophysiology are
established from which a basic understanding of neural mechanisms that control muscle
contraction under dynamic conditions exists.

Neuromuscular control is a term associated with the field of motor control, and is
used to reference those numerous and elaborate mechanisms that comprise the nervous
system and delineate their role in voluntary, involuntary, and reflexive muscle activation
(Lephart & Riemann, 2002a). Proprioception is defined as the culmination of all neural
inputs originating from the visual apparatus, vestibular system, and peripheral
mechanoreceptors (Hamill & Knutzen, 2003). The role of the peripheral
mechanoreceptors is to transform mechanical distortion (e. g., changes in joint position,
muscle length, or muscle tension) into an action potential that enters the spinal cord and
ultimately regulates reflexes and motor control (Hamill & Knutzen, 2003; Latash, 1998).

Sources of these joint proprioceptive inputs are located throughout various
structures of the body including articulations, tendons, muscles, inner ear, and both
cutaneous and deep tissues. The regulation of this interaction between the sensory
(afferent) and motor (efferent) pathways is complex and is commonly referred to as the
sensorimotor system (Hewett, 2002). Those components associated with the
sensorimotor system that contribute to dynamic joint stability are part of a larger domain

that is synonymous with those areas that dictate whole-body motor control. Thus, it is

55

generally understood that effective motor control is dependent upon accurate sensory
information concerning both the external and environmental conditions of the body
(Lephart & Riemann, 2002b).

Kinesthesia is a term that is often mislabeled synonymously with proprioception.
It is dependent upon sensorimotor activity and specifically, proprioceptive input. Thus,
kinesthesia is defined as knowledge of the position and orientation of a body segment in
space or its relative position in reference to another body segment (Latash, 1998). At a
basic level, kinesthesia allows individuals to conduct gross and precise movements
without the reliance of visual control, perform motor tasks that require multiple-limb
coordination, and adjust motor patterns with respect to the force field in which they move
(Latash, 1998).

The acquisition of functional knee joint stability is dependent upon components
of the human anatomical complex to be both pliable and versatile for various task
capabilities during locomotion. These components are typically classified as either
passive or dynamic restraint components. The passive components consist of the
ligamentous structures, joint capsules, cartilage, and the bony geometry about the
articulation, while the dynamic restraints are those components that comprise the feed
forward and feedback neural inputs (e. g., muscle spindles, golgi tendon organs) to the
skeletal muscles that literally cross an articulation (Lephart & Riemann, 20023).

Feed forward control is considered to describe actions occurring upon the
identification of the beginning, as well as the effects of an impending stimulus or event,
ofien referred to as an anticipatory action (Hewett, 2000). Feedback is a term used to

describe actions occurring in response to the sensory detection of direct effects fiom the

56

arrival of a stimulus or stimuli to the system, and is largely influenced by previous
experiences with a detected stimulus (Lephart & Riemann, 2002a; Enoka, 1994).

In the static state, the ACL provides restraint to anterior tibial translation with
respect to the femur. However, forces incurred at the joint during dynamic conditions,
such as those realized in sport, may be beyond the functional restraint capacity of the
passive qualities of the ACL. As a result, the neural recruitment of muscular forces via
an optimal interaction between the passive and active restraint systems becomes essential
in maintaining functional knee joint integrity (Pollard, Heiderscheit, Van Emmerick, &
Hamill, 2005; Huston & Wojtys, 2001).

Under normal neurophysiologic conditions, the neuromuscular system interacts
with sensory feedback from the ligament structures, muscle activity, and the joint surface
contact forces to provide essential joint stability for protection (Lephart & Riemann,
2001; Schultz & Perrin, 1999). One of the vital factors associated with producing
functional joint stability during activity is the reliance on neuromuscular control to
enhance and dictate the property of muscle stiffness. If increased muscle stiffness exists,
then there is increased joint stiffiress, thus, greater potential to prevent the incidence of
joint subluxation via ligamentous damage under those conditions that involve
circumstances of dynamic loading (Lephart & Riemann, 2001).

Lephart and Riemann (2001) have defined muscle stiffness as the ratio of change
in applied force per change in length of the muscle, and have expressed the existence of
three factors associated with this property - passive, intrinsic, and extrinsic. Passive
factors originate from the viscoelastic contributions of the non-contractile elements of the

muscle, while intrinsic factors are comprised of any number of actin-myosin crossbridges

57

existing at a given time. Reflexes comprise the third factor and contribute to muscle
stiffness via the elongation of the muscle-tendon unit.

Neuromuscular control of knee stability, and specifically muscle stiffness, is
established through both reactive (reflexive) and intentional (preparative) responses that
are mediated by proprioceptive feed forward and feedback mechanisms (Schultz et al.,
2001). Like muscle stiffness, kinesthesia or position sense is dependent upon the various
peripheral receptors (e. g., mechanoreceptors) from which the degree of activation is
reliant upon muscle length, velocity, force, joint angle, and pressure on cutaneous
receptors.

Thus, it can be affirmed that both muscle stiffness and kinesthesia are motor
byproducts in response to proprioceptive stimuli and, in essence, complete a “loop”
within the sensorimotor system. The specific mechanisms that regulate these neural
mechanisms under a variety of physiological conditions are voluminous and have been
described in intricate detail elsewhere within the literature (Hewett, Patemo, & Myer,
2002; Lephart & Riemann, 2002b; Lephart & Riemman, 2001; Latash, 1998; Enoka,
1994; Crago, Lemay, & Liu, 1990; Denier van der Gon, Coolen, Erkelens, & Jonker,
1990).

Neuromuscular Intervention

Differing sex-derived anatomical characteristics and the ethical difficulty of
prescribing oral contraceptives to mitigate ligament laxity have led a significant number
of investigators to suggest that the most direct methods of ACL injury intervention
involve the alteration of neuromuscular function. Because proprioceptive inputs define

the regulation of the dynamic restraint components, and specifically, properties of muscle

58

stiffiress and kinesthesia, physical training protocols have been devised as a means of
potentially altering particular biomechanical parameters associated with ACL injury in
sport (Mandelbaum, Silvers, Watanabe, Knarr, Thomas, Griffin, Kirkendall, & Garrett,
2005; Myer, Ford, Palumbo, & Hewett, 2005; Noyes, Barber-Westin, Fleckenstein,
Walsh, & West, 2005; Irmischer. Harris, Pfeiffer, DeBeliso, Adams, & Shea, 2004;
Hewett et al., 2002).

Determining the effectiveness of a physical training protocol on altering landing
strategy should include the ability to assess those biomechanical parameters that
represent an output function of the dynamic joint stabilizing factors (e.g., joint moments,
joint kinematics, muscle myography, and ground reaction forces). Quantification of these
parameters during locomotion enable the investigator to surmise the mechanical
contributions of muscle fibers, ultimately determined by sequences of activity patterns
generated by the CNS (Denier van der Gon, Coolen, Erkelens, & J onker, 1990; Crago,
Lemay, Liu, 1990; Brooke & McIlroy, 1990).

Previous investigations have demonstrated the potential to alter the various
proprioceptive feed forward and feedback mechanisms associated with control of the
lower extremity segments during the performance of various athletic maneuvers (Cerulli
et al., 2001; Hewett et al., 1996; Wojtys et al., 1996). Rodacki et a1. (2002) and
Heiderscheit et a1. (1998) have suggested that control organization occurs only after a
period of practice where the subjects are allowed to repeatedly solve the task
requirements and learn how to alter their muscle properties to improve a motor task. As
skill is acquired, variability within the activity is decreased ”because the CNS selects an

optimal pattern with which to achieve motor efficiency. Thus, it would appear that

59

sensorimotor accommodation and adaptation, in conjunction with CNS pre-planning, are
likely to provide neural recognition and muscular responses that inevitably create motor
programs or “engrarns” that work to correct potential motor control error that may
contribute to injurious circumstances (Hewett, 2002; Cerulli etal., 2001).

For neuromuscular response modification to occur in sport, the injury mechanism
or pattern of movement must be recognized by the sensorimotor system as potentially
debilitating. The corrective response is then initiated to modify the movement of the
involved limbs in a way that reduces or alters the stresses applied to the joint and
supporting ligaments, by ordering a different movement or reflexive strategies that
alleviate potentially damaging trauma to local structures. This strategy implies that an
altered neuromuscular response is one method to change a movement pattern and to
modify the internal forces applied to the system. An appropriate alteration of muscle
activation patterns may provide protection to those structures that are at the highest
potential for injury (Cerulli et al., 2001).

Hewett et al. (1996) examined the effect of a jump-training intervention program
on landing mechanics and lower extremity strength among high school female volleyball
players. The jump-training program was designed to decrease landing forces by teaching
neuromuscular control of the lower limb while performing a landing task. After training,
peak landing forces decreased 22% and knee adduction and abduction moments
decreased approximately 50%. In conjunction with resistance training, athletes were
trained for six weeks on jumping and landing techniques and how to utilize key verbal
cues (e. g., “on your toes”, “light as a feather”, and “recoil like a spring”) to help them

visualize particular phases of the jump.

60

 

 

 

Similar in structure to the Hewett et al. (1996) protocol, Hewett, Riccobene, and
Lindenfield (2001) introduced another six week three phase intervention protocol labeled
“sportmetrics” that included stretching, plyometrics, and selected progressive resistance
training exercises. Twelve hundred sixty-three athletes representing 43 soccer,
volleyball, and basketball teams from 12 high schools participated in the study. Three
hundred sixty-six female athletes followed the intervention protocol while 463 females
and 434 males served as controls. Of the athletes participating in the study, ten of the
untrained females, two of the trained females, and two male athletes sustained serious
knee injury during their respective competition periods. Although the study was limited
by relatively low injury numbers (five non-contact ACL injuries and five medial
collateral ligament (MCL) injuries were sustained by the untrained female athletes, while
no trained female athletes and one male athlete reported an ACL injury), the prospective
study demonstrated a decrease in serious knee injuries among those participating in a
neuromuscular intervention program.

Wojtys et a1. (1996) implemented a six week intervention program that included
placing adult volunteers into isokinetic strength, isotonic strength, agility, or control
groups to test the effects of training on muscle reaction time after an unanticipated
perturbation to the knee. The agility group significantly improved spinal reflex times of
the lateral and medial quadriceps, and the cortical response times of the gastrocnemius,
medial hamstrings, and medial quadriceps. The isokinetic training group significantly
produced lower response times after the training period and the isotonic group’s response
times did not significantly change. The investigators concluded that isotonic and

isokinetic strength training of the lower extremities did not appear to enhance muscle

61

response time, whereas agility exercises presented the potential for success with this
parameter.
Movement Competence

Movement in the sport context often exists in a constant flux of emotional,
tactical, and physical indeterminate variability and unpredictability. Thus, in order to
“prepare” for indeterminate variability, it would appear sensible to introduce tactics and
intervention techniques that assimilate as close as possible those indeterminate movement
conditions observed in practice and in competition. For validity purposes, the more
closely the patterns of movement utilized in an intervention resemble what occurs under
competitive conditions, the better the investigator should be able to ascertain how altered
proprioceptive inputs affect motor strategy, irrespective of the motor task.

Sell et a1. (2005), Hewett et a1. (2002), and Hewett (2002) have suggested the
enhancement of proprioceptive function requires coaching personnel to expose athletes to
“high-risk” maneuvers in a “controlled” or supervised environment. The authors do not
clearly delineate the term “high-risk”. However it is expressed that the intent of these
activities is to facilitate the development of multi-joint neuromuscular engrams that
combine joint stabilization, acceleration, deceleration, and kinesthesia through
intermittent protocols that progress from low—intensity simple unidirectional movement
patterns to complex multi-planar patterns of movement.

Besier, Lloyd, Ackland, and Cochrane (2001) have proposed the use of drills that
include unexpected or “unanticipated” maneuvers that can potentially refine the
neurophysiologic processes through which the CNS dictates movement. The authors

imply that familiarization in performing unanticipated rapid changes in direction rather

62

than preplanned motions directs the CNS to initiate the appropriate adjustments that may
reduce response times to the visual and mechanical stimuli experienced in competitive
sport and physical activity.

Recommendations may include, but are not limited to, initiating balance
perturbations, alternating upper extremity and lower extremity movements
simultaneously, single-leg plyometric activities, and/or rapidly changing directions
(Hewett et. a1, 2002). Rapid unplanned changes in direction under unpredictable
circumstances ofien occur frequently during competitive and practice scenarios among
popular American sports (e.g., basketball, volleyball, and soccer).

To date, few published works exist that have examined biomechanical parameters
of the knee joint of subjects performing unanticipated changes in direction of movement.
Besier et a1. (2001) examined lower limb kinematics and kinetics of 11 healthy male
soccer players who performed cutting maneuvers under both preplanned and
unanticipated conditions. Results of the study determined that performing a sidestep out
under unanticipated conditions increased external val gus moments 1.5 to 12.3 times the
magnitude of the preplanned conditions. When comparing unanticipated conditions to
preplanned, internal rotation moments and knee flexion angles were significantly higher
during the pushoff phase and external rotation moments were significantly higher during
all stance phases of the cutting task. These results suggest that changes in the movement
characteristics (e.g., deceleration, cutting angles, posture, and center of gravity) during an
unanticipated task may be concomitant with the altered execution of a motor task, thus
the potential for increased external loads applied to the knee joint when compared to the

preplanned conditions.

63

Myer et a1. (2005) examined the effects of a comprehensive six week
neuromuscular intervention program on measures of performance and lower-extremity
movement biomechanics among adolescent female athletes 15.3 i 0.9 years of age.
Participants within the experimental group demonstrated increases in knee flexion-
extension range of motion during the landing phase of box jumps, along with
concomitant decreases in valgus and varus torques. The investigators implemented an
unanticipated directional cutting maneuver but did not disclose the specific length of the
run or the angle of cut by the subject upon receiving the directional cutting cue.
Dependent upon the study design and execution of the experiment, these factors may
actually reveal anticipatory influence with regard to the running and cutting task by
inducing deceleration, or angles of cutting that exhibit an “arc-like” pattern as opposed to
an angular disposition. Consequently, it is possible the biomechanical parameters
collected in the laboratory setting may not be comparable to those conditions encountered
in competition or practice.

Cowling and Steele (2001), utilizing EMG, examined muscle burst activity of the
thigh musculature and gastrocnemius during an unanticipated-catch or no-catching task
among their subjects who landed from a jump-task associated with netball. Although
ground reaction forces were similar in magnitude for both conditions, muscle burst onset
of the quadriceps and gastrocnemius were significantly earlier when compared to the
biceps femoris during the unanticipated-catch conditions.

Besier, Lloyd, and Ackland (2003), comparing unanticipated run-and-cut
maneuvers to straight ahead running, found significantly greater muscle activity in the

lower extremity during the cutting maneuvers. The enhanced muscle activities coincided

64

with the higher internal and external rotation moments exhibited during the sidestep cut.
Additionally, there was an increase in muscle activity prior to heel strike in the straight
ahead run, suggesting a pre-programmed neuromuscular response in anticipation of
impact with the ground.

Further evidence of lower extremity muscle pre-activity prior to impact with the
ground is in concert with the findings of Neptune et a1. (1999). Utilizing EMG,
significant muscle “burst” activity of the knee flexors and extensors was evident prior to
foot contact in ten recreationally active males who performed various sidestep cutting and
v-cut maneuvers.

Investigations by Besier et a1. (2001), Cowling and Steele (2001), Neptune et a1.
(1999), and Brooke and McIlroy (1990) appear to support the premise that muscle
activation strategies may be coordinated to help stabilize the knee joint and other
supportive structures prior to impact with the ground during running and other associated
athletic maneuvers. With respect to ACL injury and the knee, Besier, Lloyd, Cochrane,
and Ackland (2001) have expressed that when potentially destabilizing forces threaten
the integrity of the anatomical structures, the CNS is capable of adjusting muscle
activation patterns to counter the large flexion loads to the knee muscles surrounding the
joint and additionally, must apply a large extension moment that may result in a net
anterior force to the tibia when the knee is near full extension. This mechanical
predisposition is thought to be a chief requisite for serious ACL injury (Lephart et al.,

2002b; Colby et al., 2000).

65

T raining for Dexterity

In the context of human movement, dexterity is defined as that ability of the
nervous system to develop a quick and simple motor solution to a motor problem
(Bernstein, 1996). To be dexterous does not propose that an individual perform
harmonious, coordinated movement patterns. Instead, the efficiency or resourcefulness
of movement is dependent upon the ability to predict the possible changes in the external
environment or changing conditions and to correspondingly plan movements.

In the analysis of movement, both qualitative and quantitative characteristics are
represented with respect to the completion of a motor task. The qualitative characteristics
are established when the movement does what is required or achieves “correctness”,
while sensory corrections or, the precision of movement can be assessed if quantitative
(biomechanical) characteristics can be evaluated. Because sport, in practice and
competition, frequently provides a venue of variant motor abundance under both
anticipated and unanticipated conditions, the enhancement of sensorimotor acuity from
the practice of a number of different motor skills provides an opportunity to form an
important background for dexterity (Bernstein, 1996).

Several investigations have assessed the effectiveness or influence of a
neuromuscular intervention program on biomechanical parameters of the knee joint
among subjects performing athletic-type maneuvers (Sell et al., 2006; Myer, et al., 2005;
Irmischer et al., 2004; Cowling & Steele, 2001; Hewett et al., 2001; Hewett et al., 1996).
These various protocols have been introduced under the premise that sensorimotor
adaptations that take place dependent upon the stimuli the proprioceptors receive during

or prior to an anticipated motor task or demand. The results of these studies appear to

66

demonstrate the potential influence that intervention programs have on altering particular
biomechanical parameters (e. g., ground reaction forces, joint moments, and/or angles of
knee flexion on landing), and add to the notion that efficient neuromuscular control is
essential to dynamic joint stability and provides a baseline of information that may lead
to undermining the problem of ACL injury among female athletes (Schultz & Penin,
1999)

Although basketball athletes routinely land from jumps of varying heights and
demonstrate changes in direction at a variety of speeds, it is believed the non-contact
nature of the ACL injury is exacerbated under those conditions where there is insufficient
time to prepare for the athletic maneuver, thus limiting response and/or introducing
inappropriate postural adjustments and the inability to generate muscle activation patterns
suitable for joint stabilization. Considering these circumstances, could the establishment
of “dexterity” at this juncture (i.e., between landing and subsequent change in direction)
provide a scenario whereby the athlete must learn to provide an immediate motor solution
to the motor problem? Is this form of motor learning best established under those
training conditions that introduce precepts of dexterity? Finally, perhaps of most
importance, if enhancing dexterity establishes the alteration of those biomechanical
parameters associated with ACL injury, is there an appropriate physical developmental
stage (e. g., childhood, adolescence, and young adulthood) when an intervention should be
implemented?

Determining when to intervene is particularly difficult to ascertain because few
studies have compared pre-pubescent to post pubescent female athletes, and in general,

studies involving the observation of biomechanical parameters of the knee among

67

adolescent female athletes are sparse. While examining kinematic and kinetic parameters
of lateral, static, and vertical landing sequences among recreationally active pre-
pubescent (mean age 9.0 i 1.0 yrs) and post pubescent (20.2 :1: 1.2 yrs) female athletes,
Hass, Schick, Chow, Tillman, Brunt, and Cauraugh (2005) found the pro-pubescent group
to land in a position of approximately 4.5 degrees greater knee flexion, albeit exhibited
greater knee extension moments and significantly greater ground reaction forces. One
major limitation of this particular study was that no maturational assessment was
conducted among the participants of the pre-pubescent group. This is a concern because
there is the underlying implication that the anatomical and physiological changes
associated with the onset of puberty may play a role in altering neuromuscular control;
thus, further research utilizing maturational assessment among adolescent female athletes
is warranted.

In an effort to alter neuromuscular function and mitigate the incidence of ACL
injury among athletic populations, the implementation of unexpected or unanticipated
movements has been suggested by Besier et al. (2001), and controlled high-risk
movements have been recommended by Hewett (2002) and Hewett et a1. (2002).
Although none of the aforementioned papers provided specific exercise criteria, these
training applications appear to be in concert with Bernstein’s (1996) premise that
selecting and implementing those special exercises and activities that enhance dexterity
become fitting, provided that they include those motor skills and sequences that introduce
an element of unpredictability, which inevitably through training, become predictable or

“manageable”. In essence, the purpose of dexterity training is to enhance the opportunity

68

for the sensory organs to increase their sensitivity during the practice of an athletic task
of significant importance.

Because the qualitative and quantitative characteristics of a motor task are subject
to the influence of practice, the precision of movement has high potential for
improvement and identifying this form of accuracy may demonstrate some transfer of
“exercisability” (Bernstein, 1996). As a result, dexterity training may be an effective
means of acquiring preferable angles of knee flexion on impact and firrther, non-reflex
muscles can be pre-programmed or “trained” to increase the joint range of motion values,
thus reducing the potential for risk of serious knee injury.

Using Bernstein’s (1996) pr0posed definition, it is apparent that dexterity training
programs can be ambiguously created to resemble a category of “exercisability” that
possesses distinct features of unpredictability that require the trainee to produce motor
“solutions”. Previous interventions including those of Mandelbaum et al. (2005), Myer et
al. (2005), Hewett et a1. (2001), Wojtys et a1. (1996), and Hewett et a1. (1996) have
utilized a variety of methods with which to intervene, thus adding to the difficulty of
deciding which exercises are the best to prevent or mitigate ACL injury. Further, in what
sequence should these exercises be implemented and for what period of time? How
frequent should this form of intervention be administered?

Because previous investigations have encountered difficulty with compliance,
standardization, or randomization of subjects (Cowling & Steele, 2001; Hewett et al.,
2001; Hewett et al., 1996), it becomes vital to gain greater insight into the application of
these injury intervention programs. In particular, the adolescent female athlete is a

specific at-risk population at variable stages of maturation that necessitates further

69

research that includes some method of maturational assessment and an opportunity to
investigate the effects of training interventions that include those unanticipated motor

characteristics inherent and prevalent in sport.

70

CHAPTER 3 ‘
METHODS

Experimental Design

To test the research hypotheses, a test-retest quasi-experimental design study was
employed. Coaches of Under 14 (years) Amateur Athletic Union (AAU) female
basketball teams were informed of the study through a Michigan AAU Basketball
intemet website forum (www.miaaugirlsbb.com) and posting. The coaches were
solicited to determine if they would be interested in providing their team as either an
experimental or control group for a study investigating the effects of a dexterity training
protocol on biomechanical parameters of the knee joint associated with landing from a
maximal vertical jump task.

The dependent variables assessed for both groups included the following: peak
ground reaction force (PGRF), peak knee joint flexion (PKJ F), time to peak knee joint
flexion (TKJF), and the peak knee extension moment (PKJ M). The independent variable
(treatment) for this study was a twice-per-week, six week dexterity training intervention
administered to the experimental group, and conducted in a manner that did not detract
from the allotted time for basketball skill training and scrimmage. The control group was
not exposed to any intervention other than those skills and tasks expected during normal

basketball practice and competition.

Participants

Upon approval of the project through the University Committee on Research

Involving Human Subjects (UCRIHS), female athletes from two youth female basketball

7l

teams were selected on a first—come, first-serve basis, from a pool of competitive teams
participating as members of the AAU within the state of Michigan. The AAU is the
premier competitive environment for female adolescent basketball athletes within the
United States. Participants typically demonstrate specific basketball skills and exhibit
fitness parameters considered superior for their respective age groupings. The criteria for
participation in the study were female, between the chronological ages of 13.0 to 14.99
years, and no previous history of knee joint injury. For this study, pertinent subject
characteristics are presented in Table 1.

Completion of the study was reliant upon four scheduled sessions with each
participating team, excluding those contacts associated with the administration of the
intervention protocol to the experimental group. These four scheduled sessions were
identified as: parent/participant informative practice session, anthropometric/vertical
jump session, pre-intervention data collection session, and the post intervention data
collection session. After the initial parent/participant informative session, the team
within the closet geographical proximity to the research institution was selected to serve
as the experimental group, while the team with the furthest geographical proximity was
selected to serve as the controls. Compliance for pre- and post intervention participation
was 100% for all participants that comprised the experimental group. One member of the
control group could not complete the post intervention data collection session due to
scheduling conflicts, and was excluded fiom the study. This resulted in four participants

for the experimental group and two participants for the control group.

72

Table 1

Participant Anthropometric Characteristics and Maturity Status

 

 

 

 

Subject Age (yr) Height (m) Mass (kg) Maturity Status
Identification (% of predicted adult stature)
El 13.4 1.57 55.5 97-06
E2 13.5 1.68 51.5 97-23
133 13.9 1.65 49.8 97-61
E4 14.2 1.75 85.4 101-15
C1 14.3 1.74 83.9 100.33
C2 13.4 1.56 50.2 96.55
Note. E = experimental group.

C = control group.

 

73

Session 1: Parent/Participant Informative Practice Session

To accommodate parent and guardian concerns with respect to the methodology,
instrumentation, potential risks, and benefits of the study, an introductory parent and
athlete meeting was conducted at a regularly scheduled practice session to inform all
participants of the higher incidence of ACL injury among female athletes when compared
to their male counterparts for the sport of basketball. In addition, the scope and design of
the study was explained in detail and the athletes were asked if they would like to
voluntarily participate in a study whose aim is to gain greater understanding of how a
dexterity training program may alter biomechanical parameters associated with the knee
joint. Afier completion of the informational session, form for youth assent for the
participants and informed consents for the parents or legal guardians were distributed
(Appendix A). Upon reviewing the youth assent and consent documents, those parents,
guardians, and athletes interested in participating in the study submitted signed forms to
the research team.

Session 2: Anthropometric/ Vertical Jump Session

Prior to the collection of pre-intervention data, all pertinent anthropometric data
was acquired at a scheduled practice session. Body mass was measured on a standard
scale (Measurement Specialties, Fairfield, NJ, USA) while subjects wore athletic shorts,
t-shirt, and socks. To derive estimates of the segment masses, segment moments of
inertia, and segment joint centers, standing height was obtained with the use of a standard
anthropometer (Siber - Hegner & Company, Zurich, Switzerland) and segmental lengths
for the right thigh, right shank, and right foot were acquired with a standardized

procedure described by Lohman, Roche, and Martorell (1988).

74

Maturity Assessment

The purpose of the maturity assessment was to estimate maturity status and
percent of adult attained height of the subject population because individuals closer to
their predicted adult stature than would be expected for their age and gender are
associated with advanced maturational status. In addition, assessment of maturity status
contributes to a broader body of knowledge that may be utilized in fiiture studies with
respect to the descriptive characteristics of this subject population.

For this project, two self-report items were used to assess the stature of the
biological parents. Parents of the participants were asked to report their stature in feet
and inches and these values were subsequently converted to centimeters. The self-
reported stature of each parent was adjusted for overestimation using an equation
developed from over 1000 measured and estimated heights of subjects (Epstein, Valoski,
Kalarchian, & McCurley, 1995).

The Khamis-Roche (1994) method is a procedure of predicting adult stature
without using skeletal age, and, is a non-invasive maturity assessment technique that
utilizes linear regressions of mid-parent stature (the average height of the two parents)
and current values of participant stature and weight. These values were determined to
provide an estimate of percentage of adult height attained upon which a biological
maturity rating was established. An underlying assumption by Khamis and Roche
(1994), while predicting adult stature, is that individuals closer to their predicted height
than would be expected for their age and gender are generally advanced in their
maturational status. Thus, two participants of the same chronological age can be of the

same height, but one may be biologically closer to adult height than the other. The

75

individual that is biologically closer to adult height is considered advanced in maturity
status compared to the individual who is further removed from predicted adult height
(Malina & Bouchard, 1991). For example, the mean percentage of adult stature attained
in girls at age 12 years is 92.61% (Bayer & Bayley, 1959). Thus, a girl who attained 95%
of her predicted adult stature at the age of 12 years would be considered advanced in her
maturity status.
Vertical Jump Test

In order to collect and standardize kinematic and kinetic data of the subjects in
their performance of a jump task, it was necessary to assess the maximal vertical jump for
all participants with the use of a VertecTM (Sports Imports, Columbus, OH) device. Each
subject’s maximal vertical jump height was calculated by subtracting their standing reach
from the jump height attained during a maximal jump and reach effort. After observing a
demonstration on how the VertecTM device is correctly used, each subject was provided
the opportunity to practice several jump and reach trials. Upon familiarization with the
instrument, standing reach was assessed by having the participant stand with feet parallel
and directly underneath the acrylic vanes of the VertecTM device. The subject was then
asked to extend the dominant arm as high as possible overhead without having any
portion of her feet leave the surface of the floor. With the dominant arm extended
completely overhead, each participant was instructed to push away as many acrylic vanes
as possible until a maximal reach height was assessed and recorded (Figure 10).

After the standing reach value was acquired for each athlete, the reset pole of the
VertecTM device was adjusted to a height from which a challenging vertical jump attempt

could be performed. While no attempt was made to alter each subject’s individual

76

jumping style, subjects were provided three trials to execute a maximum vertical jump
effort by tapping the acrylic vanes at the apex of each jump effort. The highest attained
jump effort was then assessed and recorded. Maximum vertical jump height was then
calculated by subtracting the standing reach value from the highest assessed jump effort
of the three maximal jump efforts and the resulting figure was then recorded as the
participant’s maximal vertical jump height.

To control for potential learning effects, the jumping and landing protocol used
for this study was introduced prior to any kinematic and kinetic data collection. The
jump task protocol required the athlete to conduct a maximal effort vertical jump, tap the
acrylic vanes of the VertecTM device, land, and sprint two meters either to the right or to
the left as instructed by the investigator. This landing and sprinting procedure was

repeated three times in both directions for all participants.

77

 

Figure 10. Assessment of participant maximum standing reach used in the determination

of maximum vertical jump height.

78

Session 3: Pre-intervention Data Collection Session

In concert with previous investigations, landing from a jump was chosen as the
experimental activity because a) of an association with ACL injury mechanisms, b) all
subjects were of comparable skill level, and c) landing constraints were readily
controllable in the experimental setting (Ford, Myer, & Hewett, 2003; James, Dufek, &
Bates, 2000). Participants were asked to wear athletic shorts, t-shirt, socks and the
footwear in which they typically compete or practice.

Twenty-four retro-reflective markers were placed on each subject at selected
anatomical landmarks to identify and represent two dimensional position data of the
lower and upper extremity body segments in space. The specific location of these
markers were as follows: right and left distal ulnar head, right and lefl lateral humeral
condyle, right and left acromioclavicular joint, right and left greater trochanter, right and
left lateral femoral condyle, right and left medial femoral condyle, right and left lateral
malleolus, right and left medial malleolus, right and left lateral aspect of the heel for both
feet, right and left dorsal aspect of each foot in the region of the second cuneiform bone,
right and left 5th metatarsal head, and right and left 1st metatarsal head (Figure 11).

To mitigate the potential for measurement errors, a double-sided adhesive tape
was used to affix each retroreflective marker at the designated anatomical landmarks
(over clothing and skin), and then each marker was further secured to the body with more
adhesive tape to ensure as little displacement as possible with respect to the designated

anatomical locations.

79

Acromloclavicular
joint
- Lateral -
humeral
condyle

Distal ulnar . l , ., , Medial
Head ' . femoral
‘ 7‘ ' condyle

tr"

u

Greater
trochanterw "

l

tttmmttlnnrlu-.. ....
u l
. l

.1

Lateral femoral
condyle \~...\

 

Figure 11. Retroreflective marker set-up for kinematic data collection.

80

Research Assistant

Cameras Computer

Q

 

 

 

 

 

0 U 0

Subject

 

Two meter line Two meter llne

 

U U Cameras

Figure 12. Schematic of laboratory instrumentation for biomechanical data collection.

81

Kinematic data were collected at 120 Hz with eight digital cameras (Falcon,
Motion Analysis Corporation, Santa Rosa, CA) interfaced with a one gigabyte
microprocessor computer (Dell Computer, Dallas, TX) and filtered with a low pass 4th
order Butterworth filter at a cut-off value of 15 Hz as suggested by Van den Bogert and
de Koning (1996). Three-dimensional calibration of the motion analysis system was
conducted in accordance with those specifications recommended by the manufacturer,
and one standing static trial was performed to achieve conformation and alignment of the
two-dimensional joint coordinate system to the laboratory setting. Joint angular positions
were derived from the kinematic data with zero degrees flexion defined as the knee joint
position as the subject stood upright in a standing position. From the smoothed kinematic
data, values associated with maximal right knee flexion angle on landing, and time to
peak flexion parameters in the sagittal plane were derived.

Ground reaction forces (GRF’s) under the right foot were collected at 1200 Hz
using an AMTI LG6 force platform (Advanced Medical Technology Incorporated,
Watertown, MA) with the gain set at 4000 Hz and time synchronized to the motion
analysis system. All GRF data were smoothed with a low pass 4th order Butterworth
filter at a cut-off value of 15 Hz as suggested by Van den Bogert and de Koning (1996).

Processing of all kinematic and kinetic raw data points commenced from one data
point prior to the instant of right foot contact with the force plate, until that data point
where maximal right knee flexion was derived from the landing associated with each
jump task. An EvART Version 4.2 software program (Motion Analysis Corporation,

Santa Rosa, CA) transformed retroreflective images of the markers into two-dimensional

82

sagittal plane coordinates that were temporally synchronized and interpolated so that the
number of data points matched those derived from the force plate.

Magnitude of the segmental masses for the leg and shank were derived from
Jensen (1986), and the respective moments of inertia were estimated using equations
from Winter (1990). Sagittal plane extensor moments of the right knee, defined by the
local coordinate system of the subject, were calculated using an inverse dynamics method
(Winter, 1990) that combined anthropometric, kinetic, kinematic, and GRF data exported
into a source code developed with a MATLAB 7 software package (MathWorks, Nattick,
MA, USA).

Inverse dynamics procedures were smoothed with a low pass 4th order
Butterworth filter at a cut-off value of 48 Hz (Van den Bogert & de Koning, 1996).
Right knee extensor moments were assigned a positive direction and normalized by
subject body mass as were the peak ground reaction forces on landing (Robertson,
Caldwell, Hamill, Kamen, & Whittlesey, 2004).
Pre-intervention Data Collection with Anticipated Conditions

To assess biomechanical parameters of the knee of each subject performing a
jump task under anticipated conditions, each subject was asked to jump and tap the
VertecTM at their individual assessed maximal jump height, land, and immediately sprint
to the right for two meters (Figure 13). To accommodate for the various individual
strategies associated with a jumping task, an 18-inch by one-inch by one-eighth inch strip
of balsa wood was attached with duct tape to an acrylic vane representative of each

subject’s maximal vertical jump height. An “X” was transcribed on the bottom distal

83

end of the acrylic vane to serve as a modified “target vane” for the subject while they
performed the jump task (Figure 14).

In an attempt to have the subjects land on the force platform with their right foot
when they performed the jump trials, the VertecTM was placed in a position behind the
force plate so that the modified target vane was parallel to the left side force plate border
and the transcribed “X” was at the midpoint between the left side corners of the force
platform (Figure 15). Subjects were able to identify the proper start position for the
jumps and the designated two meter sprint distance with the placement of three strips of
yellow duct tape on the laboratory floor. The center strip was placed on the laboratory
floor along the left outside edge of the force platform, while two other strips, equivalent
in length, were placed in parallel and two meters to the left and right of the center strip
(Figure 16).

After a brief warm-up and prior to performing the jumping task, subjects’ were
asked to stand upright while straddling the center strip of tape placed on the border of the
laboratory floor and force plate (Figure 16). The strip of tape was utilized in order to
have subjects initiate all jump efforts with the right leg (dominant for all subjects) on the
force plate and the left foot on the laboratory floor. The location of the force plate was
not disclosed to the subjects in order to inhibit any alteration of jump and landing
strategies.

In preparation for the jump and landing task, subjects were asked to assume a
natural ready jumping position with their heads oriented forward and arms at their side
(Figure 13). Upon the subjects confirming they were ready to jump, the principal

investigator reverse counted, “three — two — one - Go!” for each trial. On the “Go” cue,

84

each subject was instructed to initiate the jump and then tap the transcribed “X” on the
modified target vane set at each subjects’ maximal vertical jump position on the
VertecTM. Immediately upon landing, subjects were instructed to sprint to their right for
two meters past the designated strips of tape placed on the laboratory floor. Once past
the designated two meter strip of tape, subjects were told they could decelerate using as
much distance as needed until they came to a halt. Data fiom five complete trials with a
sprint to the right and five complete trials with a sprint to the left were collected for each
participant. All trials (both left and right) were summed to acquire the mean score under

anticipated conditions.

85

 

 

Figure 1'

force pl:

 

Figure 13. Subject assumes the “ready” position with the right foot in contact with the

force platform prior to a jump trial.

86

 

Figure 14. Transcribed “X” located on each subject’s designated acrylic vane of

the Vertecm.

87

 

Figure 15. View of the testing area and position of the Vertecm in proximity to the force

platform.

88

Force platform

 

Figure 16. Landing area with the right foot placed on the force platform.

89

Pre-intervention Data Collection with Unanticipated Conditions

Specific placement of equipment and subjects for the unanticipated conditions
were exactly the same as those test conditions utilized under anticipated conditions. To
generate a scenario of an unanticipated landing situation, a research assistant was
instructed to stand approximately four meters in front of the subject, with his back to the
subject, upper extremities abducted to 90 degrees with the elbows flexed, and with his
body out of the field of view of the motion analysis system (Figure 17). The research
assistant was then administered a simple hand code from the investigator that indicated a
right or left maximal effort two-meter sprint by the subject upon contact with the force
platform or the laboratory floor for each maximal jump effort. To enhance the reliability
of the hand code delivery during the trials, the research assistant was provided the
opportunity to practice the signal task with the investigators prior to data collection.

Upon affirmation of the appropriate sprint direction from the investigator, and
immediately upon hearing the subjects foot or feet make contact with the force platform
or laboratory floor, the research assistant was instructed to immediately extend at the
elbow joint and point with the index finger toward the designated sprint direction (Figure
18). No subject was provided any prior knowledge with respect to the direction of the
sprint until a landing was initiated. Testing was conducted until five quality randomized

trials in both the right and left direction were completed for each subject.

90

 

Figure I 7. Research assistant in position to provide the directional cue for the subject

with the unanticipated condition.

91

 

Figure 18. Research assistant providing the left directional cue for the unanticipated

condition.

92

Dexterity Intervention

The dexterity training protocol (Appendix C) was administered to the
experimental group twice per week over a six week time period and conducted on a
regulation high school basketball court (approximately 26 meters in length by 15 meters
in width) located in the Intramural Sports Circle Building on the campus of Michigan
State University. To accommodate travel and time limitations on coaches, parents,
guardians, and participants, each training session was conducted in addition to, and prior

to practice or competition.

After a brief dynamic warm-up that included calisthenics, participants of the
experimental group were randomly instructed to take designated positions along the
baseline of the basketball court. The general scope of instruction for each session was to
establish a continuum of motor activities initiated with the acquisition and performance
of basic fundamental motor skill patterns that gradually evolved into a series of complex
unanticipated motor tasks. In order to produce a “dextrous” environment while
conducting the training program, the administration of the specific tasks to the
participants was deliberately varied with respect to the complexity, speed, direction,
distance, amplitude, and sequence (Appendix D). These training variables were
manipulated through verbal instruction and the use of a whistle throughout the six week
training period with the intent to create unanticipated movement scenarios that may be

encountered under competitive basketball game conditions.

Upon comprehending the provided verbal instruction, each subject of the
experimental group was instructed to respond to the whistle cues and perform the various

dexterity tasks. Verbal feedback on performance of fundamental skills was provided for

93

each task as deemed necessary by the investigator. Individual learning and performance
variability among the participants with respect to the specific tasks was expected,
however, no accommodations or alterations with respect to ability of the participants and
the weekly training schedule were made by the investigators during the administration of

the six week dexterity protocol.

Post Intervention Data Collection with Anticipated and Unanticipated Conditions

Upon completion of the six week dexterity training protocol, all participants were
contacted and notified that they would have to be post tested under those conditions
similar to those experienced under pre-intervention conditions. Subject preparation and
specific placement of equipment for both the anticipated and unanticipated scenarios
were exactly the same as data collection procedures prior to the intervention administered
to the experimental group.

Data Analyses

Relevant baseline characteristics of the kinetic and kinematic parameters were
calculated and evaluated through the use of descriptive statistics, specifically, means and
standard deviations for the dependent variables under both anticipated and unanticipated
jump landing conditions. Because random assignment of intact groups was utilized, an
independent sample t-test was performed to determine if pre-existing group differences
were evident at study entry for peak ground reaction force, peak knee joint flexion, time-
to-peak knee joint flexion, and peak knee extension moment while landing from a jump
with unanticipated conditions.

To explore if potential relationships among the various dependent variables

existed, Pearson’s correlations were performed with both the anticipated and

94

unanticipated landing conditions for the post intervention time point. To test the study
hypotheses related to potential group (control vs. experimental) differences over time
(study entry vs. 6 weeks) for each of the dependent variables, a series of repeated-
measures analysis of variance (ANOVAS), utilizing a mixed model analysis, were also
conducted. Finally, a secondary aim of the study was to determine if significant pre-
intervention differences existed between the anticipated and unanticipated landing
conditions among all the involved participants. To test for these potential differences,
paired sample t-tests were conducted for each dependent variable. All statistical analyses
were conducted with SPSS Version 12.0 (SPSS Inc., Chicago, IL) utilizing a significance

value of p < 0.05.

95

CHAPTER 4
RESULTS

Pre- and post intervention means and standard deviations for the dependent
variables under anticipated and unanticipated conditions are presented in Tables 2 and 3.
At study entry, pre-existing differences were found between the experimental and control
groups for unanticipated time to peak knee flexion [t(l ,48) = -2.6, p<0.05].

Pearson’s correlations were conducted among the dependent variables and several
significant moderate relationships were found. The relationship between unanticipated
peak knee flexion angle and unanticipated time to peak knee flexion angle was strongest
(r = .72, p < .01). Several other significant (p < .05) and expected correlations emerged
among the dependent variables with anticipated landing conditions and are presented in
Table 4.

To test the study hypotheses that a dexterity training protocol would be associated
with a reduction in peak ground reaction force, peak knee flexion, time to peak knee
flexion, and peak right knee extensor moment upon landing during unanticipated
conditions, a series of repeated measures ANOVAS, utilizing a mixed model analysis,
were conducted. For the dependent variable of peak ground reaction force, the Group
(control, experimental) x Time (study entry, six weeks) interaction under unanticipated
conditions was not significant [F(1, 91) = .54, p = 0.47]. However, for the main effects
for Group [F(1, 91) = 11.1, p<0.01] and Time [F(1, 91) = 10.3, p<0.01], significant
differences between the experimental and control groups were found. For the dependent
variable of peak knee flexion on impact, the Group (control, experimental) x Time (study

entry, six weeks) interaction under unanticipated conditions was not significant [F(1, 97)

96

.007, p = .93]. Likewise, the main effect for Time was not significant [F(1, 97) = .68, p
= .41]. However, the main effect for Group [F(1, 97) = 14.6, p<0.01] was significant,
indicating noteworthy differences between the experimental and control groups.
Similarly, for the dependent variable of time to peak knee flexion on impact, neither the
Group (control, experimental) x Time (study entry, six weeks) interaction [F(1, 106) =
.49, p = .48] nor the main effect for Time [F(1, 106) = 2.9, p = .09] were significant.
However, a significant main effect for Group emerged [F(1, 106) = 31.3, p<0.01]. For
the dependent variable of peak knee extensor moment on impact, there were no
significant findings: [Group x Time: (F(1, 104) = 1.96, p = 0.17); Main effect for Time:
(F (l, 104) = .02, p = 0.88); Main effect for Group: (F (l, 104) = 3.3, p = 0.07)].

Finally, results of paired sample t-tests exhibited significant differences for all
variables of interest. Peak mean ground reaction force [t (df = 24) = -8.66, p < 0.01],
mean peak angle ofknee flexion [t (df= 23) = 5.53, p < 0.01], mean time to peak knee
flexion on impact [t (df = 27) = 2.13, p < 0.05], and mean peak knee extensor moment
[t (df = 27) = -2.93, p < 0.01] were all significantly different when comparing the

anticipated to the unanticipated landing conditions.

97

Table 2
Results for the Dependent Variables Following a Maximal Vertical Jump Landing with

Unanticipated Landing Conditions

 

 

Dependent Results of the Investigation
Variable

Peak Mean Ground Group x Time interaction: Not significant
Reaction Force Main effects for Group: Significant

Main effects for Time: Significant

 

Peak Knee Joint Group x Time interaction: Not significant
Flexion Main effects for Group: Significant
Main effects for Time: Not Significant

 

Time to Peak Knee Group x Time interaction: Not significant
Joint Flexion Main effects for Group: Significant
Main effects for Time: Not Significant

 

Peak Knee Group x Time interaction: Not significant
Extensor Moment Main effects for Group: Not Significant
Main effects for Time: Not Significant

 

 

98

 

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Table 5

Pearson ’5 Correlations for Dependent Variables for Anticipated and Unanticipated Conditions

 

Anticipated Anticipated Anticipated Anticipated Unanticipated Unanticipated Unanticipated Unanticipated
Ground Knee Joint Time to Peak Knee Extensor Ground Knee Joint Time to Peak Knee Extensor
Reaction F lexion Knee F lexion Moment Reaction F lexion Knee F lexion Moment

Force Force

 

Anticipated
Ground 1 .192 .185 .158 380* .621** .556** -0.218
Reaction
Force

Anticipated
Knee Joint 1 .577** —0.200 -0.306 .248 .374 -0.170
Flexion

Anticipated
Time to Peak 1 —0.575** —0.299 .218 370* —0.449**
Knee Flexion

Anticipated
Knee Extensor 1 .245 .005 -0. 173 .373
Moment

Unanticipated
Ground 1 -0.077 -0.299 .399**
Reaction
Force

Unanticipated
Knee Joint 1 .723** —0.427**
F lexion

Unanticipated
Time to Peak 1 -0.368**
Knee F lexion

Unanticipated
Knee Extensor . 1
Moment

 

 

* : Correlation is significant at the 0.05 level (two-tailed).
** = Correlation is significant at the 0.01 level (two—tailed).

 

101

 

 

CHAPTER 5
DISCUSSION
Variant landing and cutting movements are inherent characteristics in many
popular sports and recreational activities. This study was unique in that it involved the
acquisition and assessment of knee joint biomechanical parameters on adolescents
performing a maximal vertical jump, landing, and then sprinting in an unanticipated
direction. Because several of these biomechanical parameters have been suggested to
possess a relationship with non-contact ACL injuries among female athletes, it is of
practical value for allied health professionals, coaches, and athletes to gain greater
understanding of how these specific biomechanical parameters can be altered to
potentially attenuate the incidence of ACL injury among female athletes. Thus, the intent
of this study was to investigate the effect of a dexterity training intervention on the
following biomechanical parameters of the adolescent female knee joint during an
unanticipated condition typical of that which may be experienced in a competitive or
practice basketball setting.
Peak Ground Reaction Force
Quantifying the magnitude of the ground reaction force from a vertical jump can
reveal insight with respect to understanding the influence of this variable on lower
extremity landing mechanics. Principally, ground reaction forces contribute to the
production of kinetic energy that is associated with impact and thus, is absorbed by the
musculoskeletal structures (e. g., muscle, tendon, ligament, bone) while athletes land from
a jump (Devita & Skelly, 1992). In addition, neuromuscular responses to impact on

landing develop kinematic patterns within the lower extremities that provide an indicator

102

as to the extent with which a “desirable” landing strategy may be employed to minimize
the kinetic energy produced by those ground reaction forces on impact (Lephart et al.,
2002; Malinzak etal., 2001).

Although studies employing an intervention to alter biomechanical variables with
special landing characteristics are sparse, previous investigations have demonstrated the
ability to decrease peak ground reaction forces after a prescribed and supervised physical
training protocol. Hewett et a1. (1996) implemented a six week plyometric and strength
training program that decreased peak jump landing forces approximately 22% among a
sample comprised of adolescent female volleyball athletes. In another study utilizing
recreationally active female college students, Irmischer et a1. (2004) employed a low-
intensity plyometric exercise routine that reduced mean peak ground reaction force
values of a jump task by approximately 26.4% over a nine-week training period. It -
should be recognized that the conditions for impact in both of the aforementioned
investigations examined scenarios in which the subject was able to anticipate the
conditions of landing.

The current study employed a six week dexterity intervention to determine if the
protocol would significantly alter ground reaction forces on impact with an unanticipated
landing condition. With respect to the Group x Time interaction, this investigation
exhibited no significant decrease in mean peak ground reaction force, and interestingly,
both the experimental group and the controls yielded increases (10% and 20.7% ,
respectively) in mean peak landing force upon completing the dexterity training program.

Among both groups, only one participant (E2) demonstrated a decrease (10%) in mean

103

peak ground reaction force over the six week training period. Mean peak ground reaction
force values for each subject are displayed in Table 5.

One plausible explanation for the higher ground reaction forces may be attributed
to the extremely variant nature of the landing task prior to an unanticipated directional
sprint. Many sports, in general and basketball specifically, possess inherent multi-planar
movement responses that are dictated by the special circumstances within the context of
competition and/or practice. Unless these conditions are recognized immediately, there is
little time to develop a voluntary or preferential motor response.

Although the focus of this investigation was not associated with examining
landing strategies accompanying an anticipated condition, several participants employed
a single-limb landing technique in preparation to place themselves in an advantageous
position prior to push-off to enhance sprint performance. With unanticipated conditions
it was clear that the nature of the aforementioned landing technique was effectively
altered. All participants for all trials, pre- and post intervention, employed a double-limb
landing stance on impact, perhaps to provide a stable base of support from which the
subject could then react and then suitably align the lower extremities in the best possible
position to perform the sprint task effectively.

It is apparent the ability to execute this strategy may have been conducted at the
expense of reduced ground reaction forces and increased angles of knee flexion on
impact. The findings of this study are in accordance with those of Sell et a1. (2006) in
that under reactive or unanticipated stop jump landing conditions, significantly enhanced
ground reaction forces and decreased knee flexion was exhibited. Malinzak et a1. (2001)

and McClay et a1. (1994) have stated that the combined effects of an enhanced ground

104

reaction force and low measures of knee joint flexion on impact possess a relevant
relationship with respect to lower extremity injury. In accordance, Lephart et a1. (2002)
and Malinzak et a1. (2001) imply that the attenuation of ground reaction forces while
landing from a jump or performing a cutting maneuver is dependent upon the necessary
neuromuscular control to define those kinematic parameters (e. g., flexion, extension,
adduction, abduction) that will provide the body with the most appropriate landing

strategy on impact to prevent traumatic injury.

105

Table 6

Mean Peak Ground Reaction Force on Impact” for All Participants

 

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials Trials
E1 9 20.1 7 24.3
E2 8 18.9 10 17.0
E3 4 18.2 3 26.7
E4 9 15.3 1 1 17.3
C1 10 13.5 9 17.0
C2 10 18.5 11 20.8
a = Ground reaction force values normalized by body mass.
Note. E = experimental group. .
C = control group.

 

 

106

Peak Knee F lexion on Impact

The quadriceps exhibit lengthening in opposition to knee joint flexion during
landing and this is reflected as a net joint extensor moment representing the muscle’s role
as a shock absorber. Extensible properties of muscle allow the tissue to absorb much of
the impact associated with landing from a jump, and the degree of flexion on impact is an
indicator that appropriate force attenuation is taking place (Sell et al., 2006; McClay et
al., 1994; Devita & Skelly, 1992; Dufek & Bates, 1991). Limited ranges of motion of
knee flexion on impact present a concern because this action may induce a greater
“braking” contribution of the quadriceps thus producing excessive anterior tibial shear
forces. Hence, the resultant loads placed on the ACL may be greater and manifest
conditions conducive to producing traumatic injury (Chappel et al., 2002; An, 2002;
Malinzak, et al., 2001; Hewett, 2000).

To date, there is no current literature regarding the influence of a physical training
intervention on knee joint kinematics for subjects landing from a vertical jump with an
unanticipated condition. Although not significant, group results for the current study
demonstrated trends toward an increase in mean peak knee joint flexion on impact for
both the experimental and controls over the six week training period. Participants within
the experimental group enhanced knee joint flexion on impact with a mean value of
11.7% (6.6 degrees) while in comparison controls exhibited increased mean knee joint
flexion of approximately 2.3% (1.35 degrees).

While the dexterity training protocol did not demonstrate significant alterations
with the unanticipated landing condition, several investigations utilizing a training

intervention have demonstrated the ability to alter this parameter with an anticipated

107

landing condition. Although results were not significant, Hewett et al. (1996) enhanced
the mean knee joint flexion on impact of his subjects approximately 3.0 degrees
following a six week plyometric and strength training protocol. Following a
comprehensive neuromuscular training program consisting of weight training,
plyometrics, and balance training, Myer et a1. (2005) demonstrated significant changes in
knee flexion-extension range of motion for the right and left (4.0 and 5.0 degrees,
respectively) knee joints as the subjects performed a drop jump followed by a subsequent
vertical jump task.

Although the general group trend for the mean peak flexion values on impact for
the current study appears to be encouraging, it must be recognized that the individual
mean peak flexion data reflects abundant variation for both the experimental and control
groups (Table 6). Similar to the mean peak ground reaction forces, it is probable that the
extremely variant nature of the landing task prior to an unanticipated directional sprint
dictates the neuromuscular response as a reflection of a scenario in which there is little
time to develop a preferential motor response.

Because participants E2 (3.2 degrees), E3 (6.0 degrees), and C2 (16.8 degrees)
exhibited trends toward enhanced knee joint flexion on impact, it was expected that each
of the subjects would also demonstrate lower mean peak ground reaction forces thus
reflecting greater force absorption on impact. Interestingly, only one participant (E2)
exhibited a lower mean peak ground reaction force (- 10%) concomitant with increased
knee joint flexion on impact. These results appear to imply that ground reaction force

and angle of knee flexion on impact may not share the same relationship with the

108

unanticipated landing condition as has been reported in previous investigations with the
anticipated landing condition.

Although the trend for individual mean peak ground reaction forces were greater
for the majority of participants in both groups, individual trends toward alteration of knee
joint flexion on impact are mixed. Because there was a defined motor task (sprint)
attached with the unanticipated landing condition, it is plausible that the landing strategy
selected by the participants was closely aligned with performance outcome. DeVita and
Skelly (1992) have stated that although stiff landing techniques afford the performer the
opportunity to move faster or quickly after ground contact, this may occur at the expense
of producing potentially greater joint moment and power values which concomitantly can

be associated with a greater risk for injury.

109

Table 7

Mean Peak Knee F lexion on Landing for All Participants

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials (degrees) Trials (degrees)

E l 9 54.8 12 47.9

E2 8 57.3 1 1 60.5

E3 4 74.4 9 80.4

E4 9 70.7 1 1 70.6

C1 1 0 72.3 9 58.0

C2 1 0 3 8.9 12 55.7

 

 

Note. E = experimental group.

C = control group.

110

Time to Peak Knee F lexion on Impact

Devita and Skelly (1992) have emphasized that in order for muscle to effectively
contribute to the dissipation of kinetic energy on impact, it requires not only greater
angular ranges of knee flexion, but more time from initial impact to peak knee flexion.
Lephart et a1. (2001) concur with this position by supporting the notion that peak flexion
angle on impact and time to peak flexion angle become valuable indicators of the ability
to attenuate ground reaction forces from a landing or cutting maneuver.

For this study, neither group exhibited significant post training changes, although
the experimental group did demonstrate a trend toward enhanced mean time to peak knee
flexion upon contact with the force platform. Mean time to peak knee flexion on impact
increased from pre- to post intervention approximately 10.5%, while controls did not
exhibit alterations of this parameter. However, because of significant pre-existing group
differences and a small subject population at study entry, these results must be interpreted
cautiously and strongly imply that alterations for the dependent variable time to peak
knee flexion, may likely be due to chance.

Individual values for mean time to peak knee flexion are located in Table 7.

For the experimental participants of the study, the trend for the increased time to peak
knee flexion is in concert with an enhancement of peak knee flexion on landing.
Pearson’s correlations for peak knee flexion angle and time to peak knee flexion angle
with the unanticipated landing condition demonstrated the strongest relationship (r = .72,
p < .01) for these two dependent variables. Althoughsubject E1 experienced a decrease
in mean time to peak knee flexion concurrent with a decrease in mean peak knee flexion,

subject E2 was the only participant to decrease mean peak ground reaction force upon

lll

landing while the others actually exhibited an increase in mean peak ground reaction
force.

Similar to the findings within the experimental group, results among the control
subjects were mixed with participant C2 experiencing enhanced mean peak knee flexion
and time to peak knee flexion on impact with a concomitant increase in ground reaction
force. For several subjects, the trends exhibited within the current study are in contrast
to the expectation that mean peak ground reaction forces will decrease in concert with an
increase of mean peak knee flexion and mean time to peak knee flexion. Because
investigations determining time to peak knee flexion on impact of subjects performing
unanticipated landing conditions are rare, it is difficult to ascertain mechanisms behind
this trend among participants of both the experimental and control groups.

Generally, it has been demonstrated (Elkhart, et al., 2002; DeVita & Skelly, 1992;
Bates & Dufek, 1991) that time to peak knee flexion and peak knee flexion on impact
share a strong relationship with respect to landing while simultaneously reducing ground
reaction forces. In light of these reports, all of which have been conducted under
anticipated landing or cutting conditions, results of the current study appear to infer the
premise that the reduction of ground reaction force and an increased time to peak angle of
knee flexion on impact may not share the same relationship with the unanticipated

landing condition as is encountered with the anticipated landing condition.

112

Table 8

Mean Time to Peak Knee F lexion on Impact for All Participants

 

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials (seconds) Trials (seconds)

E1 9 0.16 12 0.14

E2 8 0.20 1 1 0.21

E3 4 0.22 9 - 0.27

E4 9 0.19 1 1 0.22

C l 10 0.19 9 0.1 8

C2 10 0.13 12 0.15

Note. E = experimental group.
C = control group.

 

 

113

Peak Knee Extensor Moment on Impact

Previous investigations have identified net knee joint extension moments acting
eccentrically to control knee joint flexion and absorb the kinetic energy associated with
landing or cutting tasks (Chappel et al., 2002; McClay, 1994). For the current study,
peak knee extensor moments exhibited no significant change from pre- to post test for
both the experimental group and controls. Examination of group trends revealed that the
experimental group experienced an increase of normalized mean peak knee extensor
moment of approximately 12.5% after the dexterity intervention, while over time,
controls demonstrated a decrease in this parameter of approximately 4.8%.

Peak knee extensor moments have been associated with peak proximal anterior
shear forces at the knee, often linked with minimal knee flexion on impact, increased
quadriceps activity, decreased hamstring activity, or a combination of all three
circumstances. It has been hypothesized that landing scenarios, where these conditions
exist, may lead to uncharacteristically high and potentially injurious knee extension
moments that are also associated with excessive ground reaction forces (Chappel et al.,
2002; DeVita & Skelly, 1992).

Among experimental group participants, only subject E2 experienced a decrease
in net right knee joint extensor moment over the six week training period. In addition,
this participant also exhibited altered biomechanical parameters (decreased ground
reaction force, increased knee joint flexion on impact, and increased time to peak knee
flexion) conducive to a decrease in net knee joint moment on impact and consistent with
previous investigations (McClay et al., 1994; Devita & Skelly, 1992; Dufek & Bates,

1991). This pattern was not typical of the other experimental group participants, the

114

remainder of which demonstrated trends among the biomechanical parameters that were
quite mixed (Table 8). Although control subject C2 did demonstrate enhanced mean
peak knee flexion, time to peak knee flexion, and a decreased net right knee extensor
moment on impact with the force platform over time, these results did not correspond
with an attenuated ground reaction force and thus, do not correspond with the findings of
McClay et a1. (1994) and Chappel et al., (1992) in that smaller ground reaction forces
typically result in smaller net knee extensor moments on impact with the ground.

Because this investigation is the only study to date that incorporates a vertical
jump-landing task with a subsequent unanticipated sprint task, it is difficult to compare
the results of this study to previous investigations that utilized anticipated landing
conditions or cutting maneuvers (Sell et al., 2006; Myer et al., 2005; Irmischer et al.,
2004; Hewett et al., 2002; Chappel et al., 2002; Malinzak etal., 2001; McClay, 1994;
DeVita & Skelly, 1992). What is readily apparent with the unanticipated landing
scenario is that the dependent variables representing the biomechanical parameters
associated with landing from a vertical jump task appear to be in contrast with the
expected trends associated with several of the aforementioned studies.

These findings suggest that changes in the landing characteristics (e.g., nature of
the drill, height of the jump, posture, and center of gravity) during an unanticipated
condition compare favorably with an altered landing task, thus the potential for increased
external loads applied to the knee joint in comparison to the anticipated landing situation.
Besier et al., (2001) have expressed that when potentially destabilizing forces threaten the
integrity of the anatomical structures, the central nervous system is capable of adjusting

muscle activation patterns to counter the large flexion loads to the knee muscles

115

surrounding the joint and additionally, must apply a large extension moment that may
result in a net anterior force to the tibia when the knee is near full extension. This
mechanical predisposition is thought to be a prerequisite for serious ACL injury (Lephart

et al., 2002b; Besier et al., 2001; Colby et al., 2000).

116

Table 9

Mean Peak Right Knee Extensor Moment” for All Participants

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials Trials

E1 9 5 .4 12 6.8

E2 8 4.0 10 3 .6

E3 4 4.7 9 5.1

E4 9 4.0 1 1 4.6

C1 10 3 .8 9 4.1

C2 10 7.5 12 6.5

 

 

a = Right knee extensor moment values normalized by body mass.

Note. E = experimental group.

C = control group.

 

117

There is compelling evidence that extrinsic factors (e.g., agonist—antagonist co-
contraction, greater extension moment values on impact, less knee joint flexion on
impact, and faster times to peak flexion) associated with ACL injury are significantly
influenced by the neuromuscular control exhibited on muscles surrounding the knee joint
(Irmischer et al., 2004; Cerulli et al., 2001; Wojtys et al., 2000; Hewett et al., 1999;
Hewett et al., 1996; Huston & Wojtys, 1996). Because proprioceptive inputs define the
regulation of neuromuscular control including muscle stiffness and kinesthesia, physical
training protocols have been devised as a means of altering the biomechanical parameters
associated with these extrinsic factors (Myer etal., 2005; Irmischer et al., 2004; Hewett et
aL,2002)

In general, the literature emphasizes two key analytical criteria to assess the
effectiveness of a physical training protocol with regard to minimizing ACL injury
among female athletes. The first is associated with the ability to objectively assess the
resultant altered biomechanical parameters that represent the output function of the
dynamic joint stabilizing factors (e. g., joint moments, joint kinematics, and ground
reaction forces) that dictate a suitable landing technique for the dissipation of the kinetic
energy on impact while landing from a jump. Second, and very likely susceptible to
many variables beyond the control of any investigation, does the physical training
program actually demonstrate the ability to minimize the frequency and severity of knee
injuries associated with sport?

This study examined the effect of a physical training program, encompassing
fundamental motor tasks and elements of dexterity, on several biomechanical parameters

(peak ground reaction forces, peak knee joint flexion, time to peak knee joint flexion, and

118

peak knee extension moments) among adolescent female basketball athletes landing .with
an unanticipated condition (unknown direction of sprint). Although previous
investigations have yielded results that provide strong evidence that physical training
programs have the ability to alter neuromuscular (pr0prioceptive) response and decrease
the incidence of serious ACL injury (Myer et al., 2005; Irmischer et al., 2004; Hewett et
al., 2002; Hewett et al., 1996), this investigation did not provide significance for any of
the proposed hypotheses. Despite a quality number of trials for each subject, the lack of
significance may in fact be associated with a major limitation of this study in that the
sample size was extremely limited, thus an understanding of the results for this study
must be interpreted cautiously. Although the subject pool was small, it should be
acknowledged that the adolescent female basketball athletes participating are considered
to possess advanced skills and motor abilities for their chronological age grouping. What
bearing this may have on the results of this study are unknown but must be considered in
light of other sample populations in previous investigations that did not utilize athletes of
comparable skill and motor ability (Myer et al., 2005; Irmischer et al., 2004; Hewett et
al., 1996). Because AAU female adolescent basketball players are typically
representative of athletes that exhibit excellent motor control and skill specifically for the
sport of basketball, it was expected that this group would possibly exhibit minimal
quantitative change among the biomechanical parameters collected. This was assumed
because the proprioceptive mechanisms during jump landings are routinely challenged
from the extensive exposure during high volume practice and competition for this elite

population.

119

In spite of the lack of statistical significance, the dexterity training did generate
desirable trends, chiefly increased mean peak flexion of the knee and mean time to peak
knee flexion that may imply the establishment of alterations of the neuromuscular system
upon impact with the ground. Of interest is the fact that an increase among these
parameters will typically produce a concomitant decrease in peak ground reaction force
and the knee joint extensor moments. Ironically, it was evident that the latter parameters
generally exhibited an increase in value, both of which are typically associated with
serious ACL injury.

Although suitable developments associated with the dexterity training protocol
did exist for this study, the specific subject population and unanticipated jump landing
conditions make it difficult to generalize these results to similar age-group or other
female basketball populations. However, it should be considered that adolescent female
athletes of lesser ability exposed to greater doses of dexterity and basketball training may
exhibit modest to dramatic alterations among the biomechanical parameters simply due to
the opportunity to refine proprioceptive mechanisms associated with a basketball specific
task such as a jump landing. As a result, it would be of interest to initiate a future study
that compared recreational female basketball athletes to those categorized as elite to
examine if the magnitude of change among the biomechanical parameters is significant

among these groups.

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Anticipated Versus Unanticipated Landing Conditions

It is important to consider that this study employed a landing scenario that is
unique in comparison to other investigations discussed within the literature. Thus it is
difficult to compare the results to aforementioned research projects to the current research
which used an unanticipated impact condition. Studies by Besier et al., (2001), Neptune
et al., (1999) and Myer et al., (2005) incorporated a setting in which the athlete, while
sprinting in a linear manner at a controlled velocity, performed an unanticipated angle-of-
cut upon receiving a change of direction stimulus. Cowling and Steele (2001) created an
unanticipated scenario utilizing a “netball” setting whereby a jump task was conducted by
the participant and then possibly and unexpectedly having a netball thrown in their
direction to produce a catch or no-catch scenario upon landing.

Because Powell and Barber-Foss (2000) have reported the rebound task during
basketball practice to be the most common event associated with knee injury among high
school female basketball athletes in the United States, the landing task for this
investigation was devised to assimilate this fiequent and fundamental skill. Practice and
competitive scenarios produce situations that require an athlete to conduct multiple
athletic tasks in an extremely variant and often, limited amount of time. As basketball
athletes are expected to jump and tip or grab the ball while rebounding, they will
eventually make contact with the ground, possibly with one limb or both subsequently
protecting the ball, passing, shooting, or dribbling.

In conjunction with a testing scenario that provided an unanticipated condition,
the dexterity intervention program for this study was devised to replicate the “controlled

high-risk movements” implied by Hewett (2002), Malinzak et al. (2001), and Besier et al.

129

(2001) to initiate balance perturbations and reproduce rapid, unpredictable changes of
direction often evident during competition and practice in the game of basketball. It
should be noted that within the literature, the aforementioned authors do not clearly
delineate the term “high-risk”. However, it is expressed that the intent of these activities
is to facilitate the development of multi-joint neuromuscular engrams that combine joint
stabilization, acceleration, deceleration, and kinesthesia through intermittent protocols
that progress from low-intensity simple unidirectional movement patterns to complex
multi-planar patterns.

To compare potential differences among the biomechanical parameters associated
with landing with an anticipated versus an unanticipated condition, a paired samples t-test
was conducted at pre-intervention inclusive of all participants, control and experimental.
This was done with the intent to firrther the position held by Hewett (2002), Malinzak et
al. (2001), and Besier et a1. (2001) that physical training programs should include those
special “hi gh—risk” intervention exercises because these tasks potentially assimilate
movements conducted by an athlete during basketball competition or practice.

Results of the paired samples t-test demonstrate that the biomechanical
parameters (mean peak ground reaction force, mean peak angle of knee flexion, mean
time to peak knee flexion, mean peak knee extension moment) evaluated in this study
possess significant differences indicating the neuromuscular system will respond with a
different landing strategy when faced with an anticipated versus unanticipated condition.
For sport medicine personnel, coaches, and physical educators that intend to initiate
injury intervention programs, the ideal that these “hi gh-risk” or unanticipated movement

tasks be included in formal physical training programs to mitigate the prevalence of ACL

130

injury appears to be a sound notion because these unexpected movements appear to be
closely aligned with what is actually happening during a rebound on the basketball court
and perhaps other uncertain motor events during the course of a competition or practice.
DeVita and Skelly (1992) assert that stiff landing techniques afford the performer
an opportunity to move quickly after ground contact to conduct an athletic task as quickly
as possible. For this study, upon landing from a maximal jump effort, the subsequent
unanticipated sprint task afforded investigators the opportunity to assess the extent of
peak knee joint flexion and time to peak knee joint flexion on impact, two parameters
associated with a “stiff” landing technique. Based upon the findings among the
dependent variables in Tables 2 and 3 at pre-intervention, it is plausible the subjects
exhibited decreased peak ranges of angular displacement about the knee and decreased
times to peak knee flexion in response to the unanticipated sprint task which was
conducted as quickly as possible upon impact. If indeed these are the circumstances with
which the neuromuscular system responds, it is evident that when one lands within the
context of an unpredictable circumstance, the neuromuscular plan crafied is one with a
tendency to provide a solution for sport task success at the expense of protecting

structures affiliated with the knee joint.

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Role of Unanticipated Training

Because unanticipated movements are readily apparent in the sport and
recreational context, it could be pr0posed that the incorporation of “unexpectant”
neuromuscular programming be included to potentially alter sensorimotor properties of
muscle about the lower extremities in order to potentially mitigate the injurious neuro-
mechanisms (e. g., latent quadriceps - hamstring firing) associated with ACL injury.
Besier et a1. (2001) furthers this ideal with the notion that “familiarizing” an athlete to
unanticipated, rapid changes in direction rather than preplanned motions will direct the
CNS to generate the proprioceptive sensitivity that will elicit appropriate neuromuscular
adjustments (e. g., quadriceps and hamstring co-contraction, increased knee joint flexion
on impact, time to peak knee flexion) within the movement. Rodacki et a1. (2002) and
Heiderscheit et al. (1998) also emphasize that neuromuscular response is enriched only
when the opportunity is provided for an individual to repeatedly solve a challenging
motor problem and potentially modify muscle properties that reflect a favorable solution
to a motor task. Consequently, as skill is improved, the variability of motor task
performance is decreased because the CNS will select a pattern that defines optimal
motor efficiency.

Although neither paper introduced by Rodacki et a1. (2002) and Heiderscheit et al.
(1998) provide a specific timeline for proprioceptive changes to occur with practice, it
would appear that sensorimotor adaptation, combining feedback and feed forward
activity of the CNS, may introduce muscular responses that generate engrams capable of
modifying the internal forces and protecting structures of the knee that are at the highest

potential for injury (Hewett, 2002; Cerulli et al., 2001). These engrams are vital because

136

ligaments become “unloaded” with enhanced muscular contributions from various co-
contracting muscles and muscle groups and the resultant joint integrity is established
through sufficient internal muscle force production to counter the external forces
produced on impact while landing from a jump (Schultz et al., 2001).

Dexterity in the Context of A CL Injury Prevention for the Female Athlete

Bernstein (1996) has proposed dexterity as that ability of the nervous system to
develop a quick and simple motor solution to a motor problem. To elaborate, to be
dexterous does not propose that an individual perform balanced, synchronized, or
coordinated movements, but rather generate an ability to forecast variant conditions in the
external environment and further, to plan responsive movements accordingly.

Although the current investigation did not yield significant changes among the
dependent variables, there were directional changes among the biomechanical parameters
indicating that the nervous system may in fact be in the process of altering some capacity
of neuromuscular control. In concert with these parameter patterns, for the dependent
variables of peak ground reaction force, peak knee flexion, and time to peak knee flexion
there were several significant statistical events associated with the main effects of Group
and Time. For peak ground reaction force, both groups exhibited increases in
unanticipated impact force from pre- to post intervention, however the magnitude of
increase was greater among the controls (20.7%) in comparison to the experimental
group (10%). Peak knee flexion increased among the controls 2.3% in comparison to an
11.7% increase for the experimental group demonstrating a significant difference for the

main effect of Group. Time to peak knee flexion was also significant for the main effect

137

of Group with the controls exhibiting no alteration in this dependent variable and the
experimental group enhancing this measure approximately 10.5%.

Except for the direction of peak mean ground reaction force, the aforementioned
findings may imply that although the current dexterity protocol did not significantly alter
the biomechanical parameters, with respect to the trends that did occur between both
groups, there indeed may be some support for the use of dexterity training to enable
positive alterations of the dependent variables associated with non-contact ACL injury.

It may be reasonable to imply that if the current intervention were applied over a longer
period than six weeks, the possibility exists that the training program may have induced
significant results congruent with the proposed hypotheses of this study. 1

What is clearly evident with respect to the diversity of the data collected is that
there exist contrasts among the traits of the biomechanical parameters in comparison to
previous investigations that have explored the anticipated landing condition exclusively.
This is of special interest because it could be argued those ACL injury prevention
programs that solely offer anticipated exercises or movements with the expectation of
altering biomechanical parameters may actually impart shortcomings with regard to what
actually occurs in the competitive and practice setting.

Investigations including the element of unpredictability within the scope of
intervention to alter biomechanical parameters of the knee are scarce. To date, only one
investigation has implemented the resemblance of an unanticipated programming element
specifically utilizing activities with unanticipated cutting maneuvers (Myer et al., 2005).
In concert with Bemstein’s (1996) proposed definition of dexterity, it is apparent that

intervention programs, including the protocol used in this study can be arnbiguously

138

created to resemble a category of “exercisability” that contain distinct features of
unpredictability and require the trainee to produce variant solutions in response to a
changing motor environment. Consequently, muscle dominant neuromuscular
adjustments (e. g., hamstring and quadriceps co-contraction) are generated to provide
varus/valgus and extensor support to the knee as it extends to stabilize while loading.
Although joint contact forces are expected to increase, joint compression via co-
contraction will enhance joint stability to acquire the limb positional control that, in
conjunction with joint surface congruency, will act to potentially unload ligaments during
mechanical loading on impact with the ground (Winthrow et al., 2006; Lloyd &
Buchanon, 2001; Demont et al., 1999).
Physical Growth and Maturation

In conjunction with muscle control factors that exude influence on the extrinsic
mechanisms that occupy a vital role with regard to non-contact ACL injury, it must be
recognized that the typical process of physical growth and maturation among female
basketball athletes demand greater attention than previously received (Davis & Ireland,
2003). An understanding of this area is special because initiation of physical maturation
may induce subsequent anthropometric and skeletal changes (e. g., limb growth, changes
in the distribution of body mass) that have the potential to alter various neuromechanical
parameters of the lower extremities as they interact with the external environment.

This scenario introduces two questions that need further elaboration: 1) What is
the appropriate age for the female athlete to be exposed to a physical training intervention
to mitigate the potential for non-contact ACL injury? 2) Second, if the physical training

intervention is applied prior to the initiation of dramatic anthropometric and skeletal

139

changes (pre-pubescent), will the participant be able to preserve the enriched feed
forward and feedback neuromechanisms associated with mitigating traumatic ACL injury
throughout adolescence and into adulthood?

In addressing the first question, because the onset of physical maturation induces
the expression of hormonal, anatomical, and behavioral change, the use of chronological
age as a defining parameter from which to decide when to implement a physical training
program to mitigate ACL injury is difficult because the timing and tempo of physical
maturation is extremely variable (Malina, 1994; Malina & Bouchard, 1991). To address
the second issue, it would be desirable to incorporate a longitudinal design that assessed
biomechanical parameters prior to the initiation of puberty until adult physical maturity
status has been achieved, and then determine if indeed these mechanical factors have
been consistent or altered over time.

To date, no published investigation has implemented a method of assessing
maturity status among adolescent female participants associated with an ACL injury
intervention project. While examining lateral, static, and vertical landing sequences
among pre-pubescent and post pubescent female athletes, Hass, Schick, Chow, Tillman,
Brunt, and Cauraugh (2005) determined the peak knee extensor moment to be
significantly greater among the pre-pubescent group during lateral and static landing
conditions. According to the authors, these findings suggest there may be maturational
considerations aside from the gender considerations that have been previously reported
(Chappel et al., 2002; Malinzak et al., 2001; Huston & Wojtys, 1996). Unfortunately,

this study did not utilize a maturity indicator to distinguish between biological and

140

chronological age, thus blurring the distinction between pre-pubescent and post
pubescent status.

Mandelbaum et al. (2005) conducted a two-year study to assess the influence of a
neuromuscular and proprioceptive intervention training program on the incidence of ACL
injury among adolescent female soccer athletes. Athletes varied in age from 14 to 18
years but unfortunately no maturity assessment was performed, although to date, this
study possesses the greatest longitudinal component in comparison to previous
intervention studies. In comparison to controls, the experimental group exhibited an 88%
decrease in ACL injury for year one, and a 74% decrease in ACL tears for year two of the
study demonstrating the effectiveness of the intervention for this chronological age group
over the two year period.

The process of maturity assessment is often awkward, unreliable and invasive,
particularly among adolescent subjects. Because the assessment of maturity status was
previously non-existent within the ACL injury intervention research setting, this
investigation implemented the non-invasive Khamis-Roche (1994) method to gain greater
perspective on the maturational status of the elite adolescent female basketball athlete
using a derived percentage of predicted adult height. The Khamis—Roche method (1994)
assumes that individuals closer to their predicted adult height than would be expected for
their age and gender possess advanced maturational status. To clarify, the mean
percentage of adult height already achieved in girls at age of 13 years is 95.96% (Bayer
& Bayley, 1959), thus a girl who has attained 97% of her predicted adult height would be
considered advanced in her maturity status. For this investigation, results of the maturity

indicator can be found in Table 1. Evaluation of the participants indicate subjects E1 and

141

E2 are extremely close to their expected predicted adult stature for age, subjects C2 and
E3 exhibit late maturational status, and subjects C1 and E4 are advanced in maturational
status with respect to predicted adult stature for age. Although these parameters are
exclusively reported as descriptive characteristics, it should be noted that it is the “post”
players, Cl and E4, that exhibit an earlier maturation status in comparison to the other
participants and interestingly play a position typically requiring greater physical
presence, tall stature and enhanced body mass.

The effect maturity status may have upon specific biomechanical parameters of
the knee joint among adolescent female basketball athletes is currently unknown and
warrants further investigation. Because the vast majority of intercollegiate female
athletes are at or close to 100% of their adult height, they no longer undergo the same
dynamic anthropometric and skeletal changes as experienced during puberty. Thus, the
use of a specific maturity indicator or defined maturity status in opposition to the use of
chronological age may provide a more reliable means through which an intervention can
be introduced to help attenuate mechanisms associated with ACL injury. This approach
may be more suitable for the adolescent female athlete because studies examining the
mechanical characteristics of the intercollegiate female basketball athlete are difficult to
use as a gauge to determine age appropriateness for the introduction of physical training

interventions.

142

CHAPTER 6
SUMMARY AND RECOMMENDATIONS
Summary

Within the United States, ACL injuries among high school female basketball
players annually occur at a rate of approximately 1 in 65 per participant (Hewett et al.,
1999). Given these incidence figures, it is estimated approximately 7,000 ACL injuries
will occur to female high school basketball athletes on an annual basis. Despite the fact
that female athletes are typically initiating sports participation at an earlier chronological
age, receive superior coaching education, and possess enhanced skills, the ACL injury
rate has not declined significantly among intercollegiate female basketball athletes in the
past decade (NCAA, 2004). Because the attenuation of ground reaction forces while
landing from a jump may be associated with an athlete’s neuromuscular capability to
devise an appropriate landing strategy, efforts to understand the role of altered
neuromuscular responses to training have been advocated to attenuate the potential for
serious knee injury and in particular, ACL tears (Lephart et al., 2002; Malinzak et al.
2001)

The specific aim of this study was to examine the effects of a physical training
program containing elements of dexterity on mean peak ground reaction forces, mean
peak knee joint flexion, mean time to peak knee joint flexion, and mean peak knee
extension moments among competitive adolescent female basketball athletes. Pre- and
post intervention biomechanical data were collected from participants immediately upon
landing from a maximal vertical jump effort and subsequently performing a sprint task in

an unanticipated direction. The results of this study did not support the proposed

143

hypotheses that the dexterity training program would produce significant changes among
the dependent variables associated with an unanticipated landing condition. In contrast,
previous investigations (Irmischer et al., 2004; Cerulli etal., 2001; Hewett et al., 1999;
Hewett et al., 1996) utilizing a physical training intervention have demonstrated the
ability to significantly alter various biomechanical parameters. However, these studies
were conducted with training circumstances utilizing anticipated cutting or landing
conditions.

Although the experimental group, employing the dexterity intervention, did not
reveal significant changes among the dependent variables in this study, several
biomechanical parameters did exhibit an unexpected albeit interesting trend with the
unanticipated landing condition. The expectation that ground reaction forces would
decrease in concert with a concomitant increase in peak knee flexion and time to peak
knee flexion was not evident, inferring the reduction of ground reaction force, enhanced
knee joint flexion and time to peak angle of knee flexion may not share the same
association with the unanticipated landing condition as is demonstrated with the
anticipated landing condition. Disassociation among these parameters was further
supported with results garnered from a paired samples t-test. All of the dependent
variables were significantly different when the anticipated and unanticipated landing
characteristics were compared between both groups.

For several participants, the dexterity protocol did generate positive trends for
knee flexion and time to peak knee flexion that may imply the initiation of alterations
upon the neuromuscular system with exposure to the intervention. The uncharacteristic

increase in ground reaction force may be reflective of a situation in which there was

144

limited time to develop a preferred motor response. Thus, athletes faced with uncertain
landing scenarios may call upon a variety of landing strategies to craft a solution for sport
task success at the expense of protecting structures associated with the knee.

Previous interventions (Mandelbaum et al., 2005; Myer et al., 2005; Hewett et al.,
2001; Wojtys et al., 1996; Hewett et al., 1996) have demonstrated success with a variety
of training methods with which to intervene, thus adding to the difficulty of deciding
which exercises are the best to prevent or mitigate ACL injury. However, based upon the
results of this study, it could be implied those intervention programs that exclusively
propose anticipated exercises or movements with the expectation of altering
biomechanical parameters may actually impart shortcomings with regard to what actually
occurs in the competitive and/or practice setting. Although not definitive, but worthy of
further investigation, perhaps the rehearsal of “dexterous” activities in combination with
successful anticipatory training methods may lead to the development of motor
“engrams” that become more predictable and controllable over time. Thus, athletes may
utilize their musculature to gain greater control of knee joint stability, enhance joint
kinesthesia, and reduce the reliance upon ligamentous structures to preserve joint
integrity while landing from a jump.

Finally, if combining dexterous exercises with other forms of intervention through
physical training does alter biomechanical parameters associated with ACL injury, it may
be important to identify an appropriate stage of physical development (e. g., childhood,
adolescence, young adulthood) with which an injury intervention program could be
implemented. Because there are expected anatomical changes associated with typical

maturation that have the potential to alter established motor patterns, it would be

145

interesting to determine if pre-pubescent athletes exposed to an injury intervention
program would be able to enhance and maintain neuromuscular control throughout
puberty and into young adulthood. Although investigations with the intent to determine
if there are maturational considerations linked to ACL injury are sparse, firrther efforts
with regard to understanding injury intervention should be encouraged to establish if
consistent exposure to physical training can mitigate the frequency and severity of knee
injuries associated with the female athlete.
Recommendations

Based upon the results of this investigation, there are several recommendations
with regard to the establishment of firture research directions concerning the ACL injury
dilemma, the application of physical training interventions, and the adolescent female
athlete.

0 Future investigations should include a larger sample population with a sufficient
number of participants in each group to determine the influence of the
intervention on the dependent variables. Researchers should identify that an
appropriate sample size is necessary to obtain a desirable effect size and power

when using multivariate analysis techniques.

0 Because it may be difficult to recruit an adequate number of elite-for-age female
basketball athletes to participate in a given study, collaborations among
institutions utilizing similar instrumentation and data collection procedures should
work in unison with their respective sample sizes to ensure adequate statistical

power is achieved.

146

 

 

 

Future investigations that include female adolescent athletes should utilize a
maturational assessment to gain greater insight into the timing of the physical
growth associated changes that have the potential to alter neuromuscular
parameters.

Because grth and maturation of the adolescent female is extremely variable
with regard to timing and tempo, the introduction of longitudinal investigations
prior to the initiation of puberty until the mature state is achieved should be
coordinated to determine what influence, if any, altered body segment and limb
parameters have on neuromuscular control. Insight into this area may help
establish a particular stage of growth that is the most appropriate to intervene in

order to enhance the effectiveness of an ACL injury intervention program.

Future research should explore variant applications involving dextrous exercises
and drills, the frequency of their application, and the prescription of training to
determine what potential impact this type of intervention may have on altering the

neuromuscular system while landing or performing cutting maneuvers.

To determine if there exist significant learning effects that account for the
quantitative changes associated with the determination of neuromuscular control,
firture investigations should examine the implications of variant motor ability
among adolescent female participants. Findings in this area may help elucidate
whether significant differences are an indicator that poor motor ability or motor
experience are a better indicator than gender with regard to the ACL injury

dilemma.

147

o In addition to quantifying the knee extensor moments on landing, the assessment
of muscular co-contraction among the quadriceps and hamstrings is an important
neuromuscular factor that offers significant insight into the alteration of knee joint
pathomechanics. Investigations utilizing electromyography (EMG) have
established that females typically generate longer electromechanical response
times, demonstrating the manifestation of muscular force at a slower rate when
compared to males (Wilk, Arri go, Andrews, & Clancy, 1999; Schultz & Perrin,
1999). Thus, the ability to assess muscle activity among the quadriceps and
hamstrings may offer insight into the effectiveness of ACL intervention protocols
and their ability to minimize quadriceps-hamstring firing latency while landing

with the unanticipated condition.

It was the intent of this research paradigm to develop an ACL injury intervention
protocol for the female adolescent athlete, easy to follow and modifiable, for application
among various recreational, sport, and physical education settings. Potentially, the
information from this study in concert with future investigations may help provide sport
scientists, coaches, and athletes gain greater insight in an attempt to manage the intrinsic
and extrinsic factors associated with non-contact ACL injury and consequently, produce

less physical and emotional strain on the competitive adolescent female athlete.

148

APPENDICES

149

APPENDIX A

IRB Approval

150

 

MICHIGAN STATE
0 I R

N VE SITY

February 3. 2004

TO: Eugene w. BROWN
204 IM Sports Circle Bldg

RE: IRB# 03-880 CATEGORY: FULL REVIEW

APPROVAL DATE: February 2, 2004
EXPIRATION DATEJanuary 2, 2005

TITLE: THE INFLUENCE OF A DEXTERITY TRAINING PROGRAM ON
BIOMECHANICAL PARAMETERS OF THE KNEE JOINT AMONG
ADOLESCENT FEMALE BASKETBALL ATHLETES

The University Committee on Research Involving Human Subjects‘ (UCRIHS) review of this
project is complete and I am pleased to advise that the rights and welfare of the human
subjects appear to be adequately protected and methods to obtain informed consent are
appropriate. Therefore, the UCRIHS approved this project.

RENEWALS: UCRIHS approval is valid until the expiration date listed above. Projects
continuing beyond this date must be renewed with the renewal form. A maximum of four such
expedited renewals are possible. Investigators wishing to continue a project beyond that time
need to submit a 5-year application for a complete review.

REVISIONS: UCRIHS must review any changes in procedures involving human subjects, prior
to initiation of the change. If this is done at the time of renewal, please include a revision form
with the renewal. To revise an approved protocol at any other time during the year. send your
written request with an attached revision cover sheet to the UCRIHS Chair, requesting revised
approval and referencing the project's IRB# and title. Include in your request a description of
the change and any revised instruments. consent forms or advertisements that are applicable.
PROBLEMS/CHANGES: Should either of the following arise during the course of the work.
notify UCRIHS promptly 1) problems (unexpected side effects, complaints. etc.) involving
human subjects or 2) changes in the research environment or new information indicating
greater risk to the human subjects than existed when the protocol was previously reviewed and
approved.

If we can be of further assistance, please contact us at (517) 355-2180 or via email:
UCRIHS@msu.edu. Please note that all UCRIHS forms are located on the web:
httpzllwwwhumanresearchmsu.edu

Sincerely,
76mg.

Peter Vasilenko. Ph.D.
UCRIHS Chair

PV: jm

CCI Anthony Moreno
1017 Delridge Rd.
East Lansing. MI 48823

151

Participant Consent Form

“The influence of a dexterity training protocol on biomechanical parameters of the
knee joint among adolescent female basketball athletes.”

Primary Investigator: Eugene Brown PhD, Department of Kinesiology,
Michigan State University
Secondary Investigator: Anthony Moreno MS, Department of Kinesiology
Michigan State University

This study is being conducted as a doctoral dissertation:

The purpose of this study is to determine the influence of a dexterity training
program on motion characteristics of the knee joint among competitive adolescent female
basketball athletes. These motion characteristics will be measured while performing a
maximal vertical jump effort, landing and then immediately followed by a side-shuffling
movement under both expected and unexpected conditions.

This study will attempt to identify changes, from prior to the training progam to
after the training program, among several mechanical characteristics of the knee. If you
are a member of the experimental group, you will be prescribed a dexterity program that
is composed of simple fundamental and basic movement tasks (e.g., jumping, skipping,
shuffling, etc.) similar to those movements you encounter in a basketball game or at
practice. Each session of the 6 week / two meetings per week dexterity program will take
approximately 15 to 20 minutes to complete. Those that are members of the control
group will follow their typical basketball practice and competition schedule for six
weeks.

The study will help to identify those mechanical factors that may reduce the risk
of knee injury and specifically, anterior cruciate ligament (ACL) damage among female
basketball athletes. The anthropometric (height, weight, limb length) data collection
session is estimated to last about 1.0 hour and each pre-test and post test kinematic and
kinetic data collection session will last approximately 1.5 hours. You will be asked to
participate in three data collection sessions to be scheduled on separate dates (Total data
collection time for three sessions approximately 3.5 hours). It is important that the
participants in the study be free of any previous orthopedic condition of the lower limbs
(e.g., thigh, shank, foot) that may hinder their ability to perform a maximal vertical jump
and shuffle maneuver. In addition, the participants should be free of allergies and
conditions associated with equine animals. The data collection process will have the
following stages:

1) General Information — After explanation and description of the study and
subject consent, a questionnaire will be distributed among the participants to
collect information with regard to self-perceived movement confidence in a
basketball game setting. This questionnaire will be administered prior the
collection of any anthropometric data.

152

2)

3)

4)

Anthropometric Measurements — All anthropometric data will be collected in
private (parents or guardians may accompany you) in the Department of
Kinesiology’s Biomechanics Research Station located in the IM Sports Circle
Building on the campus of Michigan State University.

Weight will be assessed on a standard weight balance while you are wearing
shorts and t-shirt.

Height will be assessed with a standard anthropometer.

Sitting height will be assessed with a standard anthropometer while you are seated
on a bench.

Limb lengths will be determined with the use of standard body calipers.
Specifically thigh, lower leg, and foot lengths will be measured.

Parents will be asked to provide data with respect to self-reported height as part of
a non-invasive maturity assessment.

Determining Maximal Vertical Jump — Your maximal vertical jump will be
measured with a training device called a Vertec. You will be provided plenty of
opportunity to learn and practice before the collection of the movement data.
Kinematic/Kinetic Data Collection - Kinematic data collection will involve the
use of several digital video cameras to document the movement patterns of your
body and body parts in the performance of the maximal vertical jump and landing
task. The following order of activities will be followed:

Before actual data collection, you will have 20 reflective joint markers attached to
points on the segments of the lower limbs. In addition, you will have a very small
portion of your thigh lightly abraded and cleansed in order to attach several
surface electromyography (SEMG) electrodes necessary to measure thigh muscle
activity.

You will be asked to warm up as if you were about to participate in one of your
standard basketball practice sessions.

Following your overall warm up, you will be asked to perform vertical jumps,
landings (total of 5 quality trials for both planned and unplanned landing
conditions), shufiles and sprints. Note that there is no correct or incorrect
performance. We only want to record your style of performance. You will be
asked to assume a “ready position” prior to jumping at the target phalange on a
Vertec device that will be adjusted to your determined maximal vertical jump
height.

Video cameras will be used to determine changes within the movement data and
for comparing “before” dexterity training to “after” dexterity training results.

In addition to the video recording of each jump trial, forces applied to the ground
will be collected to assist in determining the forces that exist at the knee joint
while jumping, landing and shuffling.

153

You are being asked to participate in this study because you are a competitive
athlete in a selective youth basketball league. There is no monetary benefit from your
participation. Your participation is totally voluntary, and you may chose to participate or
not, as well as to discontinue your participation at any time without any explanation. By
participating in this study you agree that the materials and data generated (video, pictures,
and measurements) may be used for research and academic purposes and may be
observed by participants within scholastic and/or research settings (e. g., classrooms,
research presentations, seminars, etc). You have also been assured that your privacy will
be protected to the maximum extent allowable by law. When this research project is
completed, an abstract of the results will be mailed to you. You may also seek personal
data for comparison of pre- and post test data.

In the unlikely event that you are injured as a result of your participation in this
research project, Michigan State University will provide emergency medical care if
necessary. If the injury is not caused by the negligence of MSU, you are personally
responsible for the expenses of this emergency care and any other medical expenses
incurred as a result of this injury.

Your signature(s) below, indicates that you give permission to the investigators to
utilize/show videotapes and still images of your participation for academic purposes
including research presentations, seminars and other clinical or classroom settings.
Should you decide to withdraw fiom the study, all videotaped sessions and/or still images
of your participation will be deleted and/or destroyed.

Signature of Participant: Date:

 

 

Signature of Parent / Guardian: Date:

 

 

If you have any questions about this study, please contact Dr. Eugene Brown
inc. 353-6491, email: ewbrown@msu.edu, or Anthony Moreno ino. 351-9734,
email: morenoan@msu.edu at the Department of Kinesiology, Michigan State University.
If you have questions or concerns regarding your rights as a study participant, or are
dissatisfied at any time with any aspect of this study, you may contact - anonymously, if
you wish- Peter Vasilenko, Ph.D., Chair of the University Committee on Research
Involving Hmrran Subjects (UCRI-IIS) by phone (517) 355-2180, fax: (517) 432-4503,
email: ucrihs@msu.edu, or regular mail: 202 Olds Hall, East Lansing, MI 48824.

 

Name of participant:
Date of birth:

 

 

Signature of participant:
Date:

 

 

154

Parental Consent Form

“The influence of a dexterity training protocol on biomechanical parameters of the
knee joint among adolescent female basketball athletes.”

Primary Investigator: Eugene Brown PhD, Department of Kinesiology,
Michigan State University
Secondary Investigator: Anthony Moreno MS, Department of Kinesiology
Michigan State University

This study is being conducted as a doctoral dissertation:

The purpose of this study is to determine the influence of a dexterity training
protocol on biomechanical parameters of the knee joint among selective adolescent
female basketball athletes. These biomechanical measures will be assessed while
performing a maximal vertical jump effort and subsequently executing a side-shuffling
movement under both anticipated and unanticipated conditions.

This study will attempt to identify potential pre-intervention and post intervention
differences of the assessed biomechanical measures among adolescent female basketball
athletes. If you are a member of the experimental group, you will be prescribed a
dexterity protocol that is comprised of simple fundamental and basic motor tasks (e. g.,
jumping, skipping, shuffling. etc.) similar in scope to those tasks encountered in a
basketball game or practice settings. Each session of the 6 week/ two meetings per week
dexterity protocol will take approximately 15 to 20 minutes to complete. Those that
comprise the control group will follow their typical basketball practice and competition
schedule for six weeks.

The study will help to identify biomechanical alterations or adaptations that may
mitigate the incidence of knee injury and specifically, anterior cruciate ligament (ACL)
distress. The anthropometric data collection session is estimated to last approximately
1.0 hours and each pre-test and post test kinematic and kinetic data collection session will
last approximately 1.5 hours. Subjects will be asked to participate in three data collection
sessions to be scheduled on separate dates (Total data collection time for the combined
three sessions approximately 3.5 hours). In addition, it is imperative that participants be
free of any orthopedic condition of the lower extremities that may hinder their ability to
perform a maximal vertical jump and shuffle maneuver, and be free of allergies and
conditions associated with equine animals. The data collection process will have the
following stages:

5) General Information — After explanation and description of the study and
subject consent, a questionnaire will be distributed among the participants to
collect information with regard to self-perceived movement confidence in a
basketball game setting. This assessment instrument will be administered prior
the collection of any anthropometric data.

155

6)

7)

8)

Anthropometric Measurements — All anthropometric data will be collected in
private (parents or guardians may accompany their child) in the Department of
Kinesiology’s Biomechanics Research Station located in the IM Sports Circle
Building on the campus of Michigan State University.

Weight will be assessed on a stande weight balance while you are wearing
shorts and t-shirt.

Height will be assessed with a standard anthropometer.

Sitting height will be assessed with a standard anthropometer while you are seated
on a bench.

Segmental lengths will be determined with the use of standard body calipers.
Specifically thigh, shank, and foot lengths will be assessed.

Parents will be asked to provide data with respect to self-reported height as part of
a non-invasive maturity assessment.

Maximal Vertical Jump Determination - Your maximal vertical jump will be
assessed with a training assessment device called a Vertec. You will be provided
ample opportunity to learn and practice prior to the collection of the kinematic
and kinetic data.

Kinematic/Kinetic Data Collection - Kinematic data collection will involve the
use of several digital video cameras to document the movement patterns of your
body and body parts in the performance of the maximal vertical jump and landing
task. The following protocol will be used:

Prior to actual data collection, you will have 20 reflective joint markers affixed to
points on the segments of the lower limbs. In addition, you will have a very small
portion of your thigh lightly abraded and cleansed in order to affix several surface
electromyography (SEMG) electrodes necessary to assess thigh muscle activity.
You will be asked to warm up as if you were about to participate in one of your
standard basketball practice sessions.

Following your overall warm up, you will be asked to perform vertical jumps,
landings (total of 5 quality trials for both planned and unplanned landing
conditions), shuffles and sprints. Note that there is no correct or incorrect
performance. We only want to record your style of performance. You will be
asked to assume a “ready position” prior to jumping at the target phalange on a
vertec device that will be adjusted to your assessed maximal vertical jump value.
Video cameras will be used to determine quantitative and qualitative data with
respect to comparing pre-intervention to post intervention results.

In addition to the video recording of each jump trial, forces applied to the ground
will be simultaneously collected to assist in the determination of forces that are
incurred at the knee joint.

156

You are being asked to participate in this study because you are a competitive
athlete in a selective youth basketball league. There is no economical benefit from your
participation. Your participation is totally voluntary, and you may chose to participate or
not, as well as to discontinue your participation at any time without any explanation. By
participating in this study you agree that the materials and data generated (video, pictures,
and measurements) may be used for research and academic purposes and may be
observed by participants within academic and/or research settings (e. g., classrooms,
research presentations, seminars, etc). You have also been assured that your privacy will
be protected to the maximum extent allowable by law. When this research is completed,
an abstract of the results will be mailed to you. You may also seek personal data for
comparison of pre- and post test data.

In the unlikely event that you are injured as a result of your participation in this
research project, Michigan State University will provide emergency medical care if
necessary. If the injury is not caused by the negligence of MSU, you are personally
responsible for the expenses of this emergency care and any other medical expenses
incurred as a result of this injury.

If you have any questions about this study, please contact Dr. Eugene Brown
inc. 353-6491, email: ewbrown@msu.edu, or Tony Moreno inc. 351-9734, email:
morenoan@msu.edu at the Department of Kinesiology, Michigan State University. If you
have questions or concerns regarding your rights as a study participant, or are dissatisfied
at any time with any aspect of this study, you may contact — anonymously, if you wish-
Peter Vasilenko, Ph.D., Chair of the University Committee on Research Involving
Human Subjects (UCRHIS) by phone (517) 355-2180, fax: (517) 432-4503, email:
ucrihs@msu.edu, or regular mail: 202 Olds Hall, East Lansing, MI 48824.

Name of participant: Date:
Date of birth:

 

 

 

Name of parent (guardian):
Signature of parent:

 

 

Mailingaddress:
Phone: e-mail address:

 

 

 

157

APPENDIX B

Physical Maturity Assessment

158

Khamis-Roche Method of Physical Maturity Assessment

To non-invasively assess the physical maturity status of all participants, height
(HT) and weight (WT) measures were acquired during the anthropometric data collection
session. This information was collected in conjunction with self-reported parental
heights. To adjust for individual tendency to overestimate height, the following equations
were implemented as provided by Epstein et al. (1995):

Adjusted Adult Height (females) = 2.803 + (0.953 x reported HT in inches)

Adjusted Adult Height (males) = 2.316 + (0.987 x reported HT in inches)

Predicted adult height of the adolescent female basketball athletes was determined
using current age, height, weight, mid-parent height and a regression equation as
proposed by Khamis and Rhoche (1994):

Predicted Height = ,8); + ,8] (HT) + ,8; (HT) + ,83 (midparent height) where;
fly is the intercept and ,8], ,62, and ,6’3 are the age and sex specific coefficients as provided

by Bayer and Bayley (1959).

Percentage of predicted adult height was used to estimate maturity status using the
following equation:
Percentage of Predicted Adult Stature = Present Stature / Predicted Adult Height
Chronological age and gender specific reference values for expected percentage of

predicted adult height were acquired from data collected by Bayer and Bayley (1959).

159

APPENDIX C

Dexterity Protocol Skills

160

Skipping. While standing upright and maintaining good posture, initiate skipping by
stepping forward, pushing off the ball of the forward foot, hopping off of that foot
and then repeating these tasks for the opposite foot. Repeat in a pattern that
assumes an alternating step — hop pattern off of each foot. Each foot will bounce
off the ground twice before the other foot strikes the ground, as the arms move in
opposition.

Back Skip. Back skipping is conducted in a similar pattern as observed when forward
skipping. The exception is that the task is initiated while stepping backwards.
Repeat in a pattern that assumes an alternating step — hop pattern off of each foot.
Each foot will bounce off the ground twice before the other foot strikes the
ground, while the maintaining the arms in a neutral position.

Crossover Sideskip. Moving in a lateral manner, cross the trail leg over the lead leg and
skip. The original lead leg then steps behind the trail leg back into the lead
position (only the trail leg crosses over). Each foot will bounce off the ground
twice before the other foot strikes the ground. Try to get your shoulders to move
with your hips as much as possible, without losing balance.

Side Shufi‘le. Side shuffling is a quick lateral stepping body movement. Start with a
natural athletic stance with the head up and focused forward. The hands are at
waist height and out in front of the body. Moving in the desired direction, push

off the balls of the feet while keeping the feet at an equal distance between each

shuffle so the feet do not come together.

161

Carioca. While keeping the head up and focused forward, assume a ready athletic
position with the hips and both legs slightly bent. While moving in a lateral
manner, the trail foot crosses in front of the lead foot. The lead foot then moves
ahead of the trail foot. The trail foot then crosses behind the lead foot and
continues this pattern for the recommended distance. Move and push off the balls
of the feet while rotating the hips while keeping the arms from swinging too far

from the body.

Front Carioca. While keeping the head up and focused forward, assume an upright

position with the hips and both legs extended. While moving in a forward
manner, the trail foot crosses in front of the lead foot as the lead foot subsequently
moves behind the trail foot. This pattern repeats for the assigned distance. Move
and push off the balls of the feet while directing the hips forward and keeping the

arms from swinging too far from the body.

Hops in Place. Pushing off with one foot, “hop” in place for the required number of
repetitions while trying to minimize displacement of the body in the horizontal or
lateral sense while landing on the push-off foot. If executed properly, you should
hop as high vertically as possible. As soon as you hit the ground, drive the arms
upward to help acquire height and power. It is important to be as quick as possible
off the ground. Repeat for the drill for the opposite leg.

Jumps in Place. Pushing off the balls of the feet, “jump” in place for the required
number of repetitions while trying to minimize displacement of the body in the
horizontal and lateral sense while landing with both feet. If executed properly,

you should jump vertically as high as possible. As soon as you hit the ground,

162

drive the arms upward to help acquire height and power. It is important to be as
quick as possible off the ground.

Single Leg Line Hops. Start on the left side of a line on the court. Pushing off of the left
foot, jump across the line, but also move forward. If executed properly, you
should move across the line and forward quickly as you land consecutively on the
push-off foot. It is important to be as quick as possible off the ground. For the
right leg, initiate the drill on the right foot. This drill can also be performed in the
backward sense.

Double Leg Line Jumps. Start on the left Side of a line on the court. Pushing off with
both feet, jump across the line, but also move forward. If executed properly, you
should move across the line with both feet quickly. As soon as you hit, drive
across the line and forward. It is important to be as quick as possible off the
ground. This drill can also be performed in the backward sense.

Side Shuflle Drill. This drill requires the use of the primary investigator to give
commands to the athlete with the use of a “single” or “double” whistle. This drill
starts with the athlete in a start position and on the baseline of the basketball
court. When the start command is given, the athlete will start by shuffling to the
midcourt. When the “single” whistle is sounded, the athlete will shuffle in the
opposite direction back to the starting point. If the “double” whistle is given, the
athlete will perform a 180 degree turn and move in the same direction toward the
midcourt. The single and double whistle commands will be interspersed while the

athlete performs the side shuffling task.

163

Carioca Drill. This drill requires the use of the primary investigator to give commands to
the athlete with the use of a “single” or “double” whistle. This drill starts with the
athlete in a start position and on the baseline. When the start command is given,
the athlete will start by carioca to the midcourt. When the “single” whistle is
sounded, the athlete will shuffle in the opposite direction back to the starting
point. If the “double” whistle is given, the athlete will perform a 180 degree turn
and move in the same direction toward the midcourt. The single and double
whistle commands will be interspersed while the athlete performs the side

shuffling task.

164

APPENDIX D

Dexterity Training Program

165

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600003 000 00 000008 0N0 ...... 0080 >080 ...... 0000000 00300002030080 08000070

800003 000 00 000008 0.00 ...... 0080 >080 ...... 00200000 008000020020 08000070

300003 000 00 000008 08 ................ 0080 >080 ....... 0000000800020 0800002

 

 

0000000 008 0:-8083 00880>Q

 

 

.90 000000 ”00.000830 00.0.000me

3 208%

170

 

0000000 008 0300 0000 ......... 00000080280080

 

800008 WE xmv 000003 00 mom 00830080 0080.0 w2 20:0Q

0000008 WE 008 000003 00 mom 008300080 0000 w2 2w00m

000008 WE xmv 000003 00 won 0083000 0080.0 w2 20:0Q

000008 03 xmv 000003 00 mo.“ “0083000 0000 w2 2w00m

$00008 0m 09 000003 20:00 000 00 00:0 000w00

cm: \3 0000000 0880 000 00 8000080 0000003 20000 000 00 02 008 0030 8000080 080000< 0
800008 0N xmv 000003 20:00 000 00 00:0 000w00

of \3 0000000 0880 000 00 000000 ”000003 200000 000 00 002 008 00w0 200000 0800000~ .

$00008 0m KS 00003 000 00 0000000 00 0w0800 \3 002 008 00000 8000080 0800002 0

800008 0N xmv 000003 000 00 0000000 00 0w0800 \3 002 008 00w: 000000 0800002

800008

03 200003 20:00 00 00000000 00>000000 ...... 200003 2w000 00 00000000880020 080000<

300003 000 00 000008 03 ...... 0200000 00800002030080 0800002

300003 000 00 000008 03 ...... 000000000 0050000200000 08000040.

0000003 000 00 000008 08 .................... 0000008000000 080000<

G x 3 .0080: 0080 ”0020 00 008:0 w2 20:0Q

 

 

0000000 008 00-8083 00880>Q

 

 

00 000000 “000000.000 00.0.000ka

2 2080‘

171

APPENDIX E

Participant Body Segment Parameters for Inverse Dynamics Procedure

172

Table 16
Whole Body and Lower Extremity Anthropometric Parameters of Stature, Body Mass,

and the Right Thigh, Shank, and Foot for All Participants

 

 

 

Subject Stature (cm) Mass (kg) Right Thigh Right Shank Right Foot
Length (cm) Length (cm) Length (cm)

B] 157.2 55.5 41.5 34 23

82 167.5 51.5 42.5 38.6 23.5
E2 165.4 49.8 40.5 36.6 23.8
E4 174.9 85.4 45.5 39.8 25.5
C] 174.3 83.9 43.5 38.9 24.5
C2 155.6 50.2 41 38.6 24.1

Note. E = experimental group.
C = control group.

 

 

173

APPENDIX F

MATLAB Source Code for Inverse Dynamics Procedures

174

MA T LAB Source Code for Inverse Dynamics Procedures
no% Converts ANC captured from MAC to force data for both leg & foot

% work on:
% baseline error at beginning used (but can change over time!)
% header names on saved files
0/.
% matrices named in square brackets to provide output
function []=TonyJump; %[ZYsum,XCPsum]=AMTI_FP;
clear all
close all
%
% start menu
prompt= {'Enter data path of key time file:','Enter name of key time file (e. g.
keytimes.txt):',...
'Kinematics Sampling frequency','Kinematics Smoothing cutoff frequency (use 0 if
already smoothed)',...
'Force smoothing (use 0 if already smoothed)',‘Force plate sampling frequency',....
'Enter start trial (from 1 to n)','Enter end trial (from 2 to n)',...
'Inverse dynamics smoothing cutoff frequency (use 0 if already smoothed',...
'Save data? (yes)','Enter output directory','0utput suffix'};
title='lnverse dynamics for 2 joints';
lines=l;
def:{'P:\keyfiles\','keyfile_kpost34.txt','120','0','0','1200','1','1','O','no','P:\Output\','__kpost'
};
% Change 3 things: keyfile name; end row (e. g. 34); output name (6. g. % kpost)
% keyfile_kpost34.txt keyfile_kpre28.txt
% keyfile_lpost31.txt keyfi1e_lpre24.txt keyfile_rpost33.txt keyfile__rpre26.txt
% keyfileO72204.txt 176

 

answer=inputdlg(prompt,title,lines,det);
fileloc=char(answer{ 1 });
keyfile=char(answer {2 } );
SF=str2num(answer {3 });
CF=str2nurn(answer{4} );
CFfp=str2num(answer { 5 } );
SFfp=str2num(answer {6 } );
starttrial=stanum(answer {7 } );
endtrial=str2num(answer {8 } );
CFid=str2num(answer {9} );
savedata=char(answer{ 1 O} );
outputdir=char(answer{1 1 });
outsuffix=char(answer{ 1 2});

% Force plate settings

175

gain=4000;
voltage=l O;
range=1 0;
mat=0.01 ;

%
% set data path
data _path = [fileloc];
eval(['cd ' data _path]);
[filedir subdir2 subdir3 subdir4 subdirS horse horseZ horse3 horse4 trialno...

suffix startt endt FPfile cond BM prepost]

=textread(keyfile,‘%s %s %s %s %s %s %s %s %s %d %s %d %d %s %s %d %s');
[an nc1]=size(filedir);

 

%

% define output names before loop

sumfx=[];sumfy=[];sumfz=[];kneeall=[];ankleall=[];

Jannkle=[];JFyankle=[];Mankle=[];Jkanee=[];JFyknee=[];Mknee=[];

RKneeDis=[];

%

for i=startt1ial:endtria1 % end at bottom

fileloc=char(strcat(filedir(i,:),subdir2(i,:),subdir3(i,:),subdir4(i,:),subdir5(i,:)));

fileloc=strrep(fileloc,'none',"); %replaces text

trcfile=char(strcat(horse(i,:),horse2(i,:),horse3(i,:),horse4(i,:),...
num23tr(trialno(i,:)),suffix(i,:),'.trc'));

trcfile=strrep(trcfile,'none',"); %replaces text

data _path = [fileloc];

eval(['cd ' data _path]);

 

 

%
% Calibration matrix

% Columns Fx, Fy, Fz, Mx, My, Mz

% Rows Vx, Vy, Vz, VMx, VMy, VMz

Cale=[11.8317 -0.041 -O.1199 -0.0981 -0.2502 0.3295];
CalVy=[0.0179 12.0391 -O.2026 0.0599 -0.0271 0.1275];
Cale=[-0.1007 0.0781 49.185 0.1032 0.0623 0.1413];
CalMx=[0.0175 0.035 -0.0064 11.1411 -0.0553 0.045];
CalMy=[0.0345 -0.0525 -0.0381 -0.043 7.8813 0.0368];
Cale=[-0.0219 -0.0632 -0.1123 -0.0877 0.0567 4.2467];
% Calibration formula (Newtons per bit)

Nperbit= 1 /((4096/(2*range))*(gain*voltage*0.000001 ));

 

% Centre of force plate correction
offsetx=-0.000765;
offsety=0.000097;
offsetz=-0.0591 16-mat;

176

% -

% Reads in *.anc file

[Time Vx Vy Vz VMx VMy VMz EMG] EMGZ EMG3 EMG4 EMG5 EMG6 EMG7
EMGS Blank]...

 

=textread(char(FPfile(i)),'%f%d%d%d%d°/od%d%s%s%s%s%s%s%s%s%s‘,'headerlines'

.11);
RawF=[Vx Vy V2 VMx VMy VMz];

 

%
% smoothing (4th order Butterworth. Not damped)

SmoothV=RawF;

if CFfp>0

SmoothV=Butterfilter(CFfp, SFfp, RawF);
end

% [Bb,Ab] = butter(2,CFfp/(SFfp/Z),'10W') ;
% smoothtemp=filtfi1t(Bb,Ab,RawF);
% SmoothV=smoothtemp;

%
Startfp=(startt(i)*(SFfp/SF))-1; %-1 needed to account for header rows
Endfp=(endt(i)*(SFfp/SF))-1;

 

SmoothV=SmoothV(Staxtfp:Endfp,z);

% Baseline correction
OffsetFx=mean(RawF(Startfp-50:Startfp-1 ,1 ))*Nperbit;
OffsetFy=mean(RawF (Startfp-50:Startfp-1 ,2))*Nperbit;
Offseth=rnean(RawF(Startfp—50: Startfp- l ,3 ))*Nperbit;
Offseth=mean(RawF(Startfp-50:Startfp-1 ,4))*Nperbit;
OffsetMy=mean(RawF(Stathp-50:Startfp-1,5))*Nperbit;
Offseth=mean(RawF(Startfp-50:Startfp-1 ,6))*Nperbit;

%Data: combines smoothing/calibration/baseline correction/plate centre offset
FVxCale=Nperbit*(SmoothV(:, l ).*Cale(:,1)+SmoothV(:,2).*Cale(:,2)+SmoothV(:,
3).*Ca1Vx(:,3)...

+SmoothV(:,4).*Ca1Vx(:,4)+SmoothV( :,5).*Cale(:,5)+SmoothV(:,6).*Cale(:,6))...

+OffsetFx;
FVyCalVy=Nperbit*(SmoothV(z,1).*CalVy(:,1)+SmoothV(:,2).*CalVy(:,2)+SmoothV(:,
3).*CalVy(:,3)...

+SmoothV( :,4).*CalVy(:,4)+SmoothV( :,5).*Ca1Vy(:,5)+SmoothV(:,6).*CalVy(:,6))...

177

+OffsetF y;
FVzCale=Nperbit*(SmoothV(:,l ). *Cale(:,1 )+SmoothV(:,2).*Cale( :,2)+SmoothV(:,
3).*Cale(:,3)...

+SmoothV(:,4).*Cale(:,4)+SmoothV(:,5).*Cale(:,5)+SmoothV(:,6).*Cale(:,6))...
+Offseth;

MVxCalMx=Nperbit*(SmoothV(:,1 ).*CalMx(:,1 )+SmoothV(:,2). *CalMx(:,2)+SmoothV

(:,3).*CalMx(:,3)...

+SmoothV(:,4).*CalMx(:,4)+SmoothV(:,5).*CalMx(:,5)+SmoothV(:,6).*CalMx(:,6))...

-FVyCalVy*offsetz-FVzCalVz*offsety+0ffseth;
MVyCalMy=Nperbit*(SmoothV(:,1).*CalMy(:,1)+SmoothV(:,2).*CalMy(:,2)+SmoothV
(:,3).*CalMy(:,3)...

+SmoothV(:,4).*CalMy(:,4)+SmoothV(:,5).*CalMy(:,5)+SmoothV(:,6).*CalMy(:,6))...

+FVxCa1Vx*offsetz+FVzCale*offsetx+OffsetMy;
MVzCale=Nperbit*(SmoothV(:,l ).*Cale(:,1)+SmoothV(:,2).*Cale(:,2)+SmoothV(
:,3).*Cale(:,3)...

+SmoothV(:,4).*Cale(:,4)+SmoothV(:,5).*Cale(:,5)+SmoothV(:,6).*Cale(:,6))...
-FVxCa1Vx*offsety-FVyCalVy*offsetx+0ffseth;
F orceN=[FVxCale FVyCalVy F VzCale MVxCalMx MVyCalMy MVzCale];

%
% interpolate from 1 in increments of r/101 to size (i.e. make 101 length)
ForceTemp=ForceN;

[nr nc]=size(ForceTemp);

newsize=101 ;

% to keep first/last same as orginal use 1:(nr-1)/(newsize-l ):nr
Force]01=[interp1(ForceTemp,l :(nr-1)/(newsize-1):nr,'spline')]; %add ' at end if only 1

 

sumfx=[sumfx,Force1 01(:,1)];
sumfy=[sumfy,Forcel 01 (:,2)];
sumfz=[sumfz,Force1 01 (1,3)];

-_-_1:orce101(:,5)./ForceIOI(:,3);
ay=Force101(:,4)./Force101(:,3);

dataforceall=[Force101(:,1),Force101(:,2),Force101(:,3)]; % use x in second column
dataforceall(:,4)=ax(:,:)+O.336; % only need 1 offset correction for 2D (both for 3D)
dataforceall(:,5)=ay(:,:); % -0.9911 18;

% improve end values of ay
dataforceall(l ,4)=dataforcea11(2,4)-dataforceall(3 ,4)+dataforceall(2,4);
dataforceall(1 01 ,4)=dataforceall(l 00,4)-dataforceall(99,4)+dataforceall(1 00,4);

178

% %
% loads kinematics
rawkine=dlmread([trcfile],'\t',[startt(i)+5 2 endt(i)+5 88]);
% converts mm to m

rawkine=rawkine/ 1 000;

[nr nc]=size(rawkine);

KineTemp=rawkine;

 

% smoothing (4th order Butterworth. Not damped)

if CF >0

Smoothkine=Butterfilter(CF, SF, rawkine);
KineTemp=Smoothkine; % can add dataraw to clipboard
end

% interpolate from 1 in increments of r/101 to size (i.e. make 101 length)
newsize=101 ;

% to keep first/last same as orginal use 1:(nr-1)/(newsize-l):nr

Kinel 01 =[interp1 (KineTemp, 1 :(nr-1)/(newsize-1 ):nr,'spline')]; %add ' at end if only 1

% new SF
newSF=SF/(nr/newsize);

0A
%Calculate segment angles in 3D (make, e. g, z zeros for 2D)
kneeraw = [Kine101(:,10) Kine101(:,11) KinelOl(:,12) Kine101(:,73) Kine101(:,74)
Kine101(:,75)...

Kine101(:,73) Kine101(:,74) Kine101(:,75) Kine101(:,76) Kine101(:,77)
Kine101(:,78)];
kneea=angle2d(kneeraw); %calling function angleZd
kneeall=[kneeall,kneea] ;
radkneea=kneea/ (1 80/pi);

% V_knee V_ankle V_shankcom V_midtoe V_footcom
%73 74 75 76 77 78 79 80 81 82 83 84
85 86 87

ankleraw = [Kine101(:,73) Kine101(:,74) Kine101(:,75) Kine101(:,76) KinelOl(:,77)
Kine101(:,78)...

Kine101(:,76) Kine101(:,77) Kine101(:,78) Kine101(:,82) KinelOl(:,83)
Kine101(:,84)];
anklea=angle2d(ankleraw);
ankleall=[ankleall,anklea];
radanklea=anklea/(1 80/pi);

% Simpler 2D angle method

179

% thighsa=1 80/pi*(pi-(atan2((Kine101(:,12)-Kine10l(:,15)),(Kine101(:,10)-
Kine101(:,l3)))));

% shanksa=180/pi*(pi-(atan2((Kine101(:,l5)-Kine101(:,21)),(Kinel01(:,13)-
Kine101(:,19)))));

% kneea=180-(thighsa-shanksa);

% .

%Input parameters for knee displacement
RKneeDis=[RKneeDis,Kine101(:,73)];

 

 

%
% Input parameters for inverse dynamics
difiime=1/newSF; %new sampling frequency

for jjj=l :2

switch jjj
case 1
% markerl=85; % ankle COM
forcepoint=dataforceall(:,4); % ay force plate
originheight=0; %mean(Kine101(:,84));
x1=Kine101(:,77); % ankle
y1=Kine101(:,78); % ankle
segmass=repmat(0.021*BM(i),101,1);
minertia=repmat(0.475,101,1); %0.004

jangle=radanklea;

jointforces(:,l )=dataforceall(:,1); % braking must be -ve? x is used for TonyJump
jointforces(:,2)=dataforcea11(:,3);

premoment=repmat(0, 1 01 ,1);

% COM ankle location
comx=Kine101(:,86);
comy=Kine101(:,87);

case 2

% markerl=79; % shank COM
forcepoint=Kine101(:,77); % ankle
originheight=Kine101(:,78); %ankle
x1=Kine101(:,74); % knee
y1=Kine101(:,75); % knee
segmass=repmat(0.053 *BM(i),] 01,1);
minertia=repmat(0.302,101,1); %0.065

jangle=radkneea;
jointforces(:,l )=Jannkle(:,i);
jointforces(:,2)=J Fyankle(1,i);
premoment=Mank1e(:,i);

180

% COM location
comx=Kine101(:,80);
comy=Kine101(:,81 );

end
%
% COM accelerations
segcom=[comx,comy,jangle];
accels=repmat(0,1 01 ,3);
accels(2:100,:)=(segcom(3:101,:)+segcom(1:101-2,:)-2*segcom(2:101-1,:))/(diftime"2);
% finds first 1 and last 1 and adds
comrl =(accels(2,:)-accels(3,:))+accels(2,:);
comr2=(accels(1 OO,:)-accels(99,:))+accels(1 00, z);
segcomacc=[comr1 ;accels(2: 100,:);comr2];
jointaccx=segcomacc(:,1 );
jointaccy=segcomacc(:,2);
angacc=segcomacc(:,3);

 

%

% J ointFx=jointforces( :,1)-segmass.*jointaccx; % Winter book

% J ointFy=jointforces(:,2)-segmass.*jointaccy-segmass*9.81; % Winter book

J ointFx=-(segmass.* jointaccx-j ointforces(:, l )); % Enoka book

JointFy=-(segmass.*jointaccy—segrnass*-9.81-jointforces(:,2)); % Enoka book
%

 

% smoothing joint force
if CFid>0
J ointF x=Butterfilter(CFid, newSF, J ointFx);
J ointFy=Butterfi1ter(CFid, newSF, J ointF y);
end

 

%
J ointMomeanremoment...

+(ab s(x1 -forcepoint). * j ointforces(:,2)). ..

-(abs(y1 -originheight).*jointforces(:,1 )). ..

-(abs(x1-comx).*segmass*-9.81)...

+minertia.*angacc...

+segmass.*jointaccx.*abs(y1-comy)...

+segmass.*jointaccy.*abs(x1-comx); % Enoka book

%
% output

switch jj j

case 1

J annkle=[J annkle,J ointF x];
J Fyankle=[J Fyankle,J ointF y];

 

181

Mankle=[Mankle,JointMoment];

case 2

J F xknee=[J F xknee,J ointF x];

J Fyknee=[J Fyknee,J ointFy];
Mknee=[Mknee,JointMoment];
end

end % fi'om for at begin of inverse dynamics
%

 

% end % from switch at begin of inverse dynamics
%

 

 

 

 

1

end %from beginning

figure

subplot(3,2, 1)

plot(sumfx); xlabel('Fx'); xlim([0 100])
subplot(3,2,3)

plot(sumfz); xlabel('Fz'); xlim([0 100])
subplot(3,2,5)

plot(sumfy); xlabel('Fy'); xlim([0 100])
subplot(3,2,4)

plot(kneeall); xlabel('Knee angle'); xlim([0 100])
% subplot(3,2,2)

% none

subplot(3,2,6)

plot(ankleall); xlabel('Ankle angle'); xlim([0 100])

figure

subplot(3 ,2, l)

plot(Jannkle); xlabel('Jannkle'); xlim([0 100])
subplot(3,2,2)

plot(J F xknee); xlabel('J F xknee'); xlim([0 100])
subplot(3,2,3)

plot(JFyankle); xlabel('JFyankle'); xlim([0 100])
subplot(3,2,4)

plot(J F yknee); xlabel('J F yknee'); xlim([O 100])
subplot(3,2,5)

plot(Mankle); xlabel('Mankle'); xlim([0 100])
subplot(3,2,6)

plot(Mknee); xlabel('Mknee'); xlim([0 100])

fi gure

182

subplot(2,] ,1)
plot(RKneeDis); xlabel('LKneeDis'); x1im([0 100])
subplot(2,1 ,2)
plot(RKneeDis); xlabel('RKneeDis'); xlim([0 100])

 

%

% saves data

switch savedata

case 'yes'

dlmwrite([outputdir 'sumFx' outsuffix '.txt'],sumfx,'\t');
dlmwrite([outputdir 'susz' outsuffix '.txt'],sumfz,'\t');
dlmwrite([outputdir 'kneeA' outsuffix '.txt'],kneeall,'\t');
dlmwrite([outputdir 'ankleA' outsuffix '.txt'],anldeall,'\t');
dlmwrite([outputdir 'Mankle' outsuffix '.txt'],Mankle,'\t');
dlmwrite([outputdir 'Mknee' outsuffix '.txt'],Mknee,'\t');
dlmwrite([outputdir 'RKneeDis' outsufiix '.txt'],RKneeDis,'\t');

end

% sumfx=[];sumfy=[];sumfz=[];kneeall=[];ankleall=[];

% J annkle=[];JFyankle=[];Mankle=[];Jkanee=[];JF yknee=[];Mknee=[];

 

%

 

 

 

% functions (1 of 1)

 

%

 

 

 

% smoothing (4th order Butterworth. Not damped)

% Input: SF, CF and Rawdata

% Output: Smoothdata

function [Smoothdata]=Butterfilter(CF, SF, Rawdata)

[nrows ncols]=size(Rawdata);

CFa=CF/0.802; % Adjusts 2nd order for 4th order (i.e. n=2 for second pass) using:

%=CF/0.435 i.e. SQRT(2"(1/(2*n))-1) for damped. Also, later Wc=SC*2

%=CF/O.802 i.e. (2"(1/n)-1)"0.25 for undamped. Also, later Wc=SC*sqrt(2)

SC=tan(pi*CFa/SF);

Wc=SC*sqrt(2); %Undamped is Wc=SC*sqrt(2) If damped is Wc=SC*2

M=1+Wc+SCA2;

aO=SCA2fM;

a1=2*a0;

a2=a0;

b1=2*(1-SC"2)/M;

b2=(Wc-SC"2-1)/M;

Smoothfirst=zeros(nrows,ncols);

for r=3 :nrows

Smoothfirst(r,:)=Rawdata(r,:)*aO+Rawdata(r-1 :r-l ,:)*a1+Rawdata(r-2:r-2,:)*a2...
+Smoothfirst(r-1 :r-l ,:)*b1+Smoothfirst(r-2:r-2,:)*b2;

183

end
Smoothreverse=flipud( Smoothfirst);
Smoothsecond=Smoothreverse;
for r=3 :nrows
Smoothsecond(r,:)=Smoothreverse(r:r,:)*a0+Smoothreverse(r-1 :r-
1,:)*a1+Smoothreverse(r-2:r-2,:)*a2...

+Smoothsecond(r-1 :r- 1 ,:)*b1+Smoothsecond(r-2zr-2,:)*b2;
end
Smoothdata=flipud(Smoothsecond);

 

%

 

 

 

% functions (2)

 

%

 

 

 

% Modified so that input is 12 variables, so calculates 3D angle

function [alpha]=angle2d(data)

% function [alpha]=ang162d(data)

% Description: Calculates the angle between 2 vectors (given by pairs of points)
% in 2 dimensions.

% Input: data: data = [Plx Ply P2x P2y P3X P3y P4x P4y]

% Note that "data" can have several rows (6. g. different time

% points).

% Output: alpha: angle (in deg) between the vectors P1-P2 and P3-P4
% Author: Christoph Reinschmidt, HPL, The University of Calgary
% Date: October, 1994

% Last Changes: November 28, 1996

% Version: 1.0

if ~(size(data,2)==12)
disp('Error: # of rows of input matrix has to be 121')
return;

end

% % "assigning" zero to the z-coordinates
% tmp=data; data=[]; data(:,[1 2 4 5 7 8 10 11])=tmp;
% data(size(data,] ),12)=[0];

r1=data(:,1 :3); r2=data(:,4:6); r3=data(:,7:9); r4=data(:,10:12);
v1=rZ-r1; v2=r4-r3;

% Preassigning alpha to speed up program
alpha=zeros(size(v1 ,1 ),1 );

for i=1 :size(vl ,1);

184

vect1=[v1(i,:)]'; vect2=[v2(i,1)]';
x=cross(vect1 ,vect2);

alphacos=rad2deg(acos(sum(vect1.*vect2)/(nonn(vect1)*norm(vect2)))); % calling a
function

FX(3,1);
% % Determining if alpha b/w O and pi or b/w -pi and O
% if sign(y)==-1; alphacos=-a1phacos; end
a1pha(i,:)=[a1phacos];
end

 

%

 

 

 

°/o functions (3)

 

%

 

 

 

function [out]=rad2deg(in)

% function [out]=rad2deg(in)

% Description: Conversion of radians to degrees applied to the entire matrix
% Input: in (values in radians)

% Output: out (values in degrees)

% Author: Christoph Reinschmidt, HPL, The University of Calgary

% Date: October, 1994

% Last Changes: November 29, 1996
% Version: 1.0

out=in.*(l 80/pi);

 

 

%

 

 

185

APPENDIX G

Participant Mean Value Data for the Dependent Variables

186

Table 17

Pre-intervention Mean Values for the Dependent Variables of Each Subject during

Landing with Anticipated Conditions

 

 

Subject Mean Peak Mean Peak Knee Mean Time to Mean Peak
Identification Ground F lexion Angular Peak Knee Right Knee
Reaction Force Displacement on F lexion Angular Extensor

on Impact‘1 Impact (degrees) Displacement on Moment on
Impact (3) Impactb
E1 6.8 79.8 0.30 3.8
E2 8.0 64.7 0.19 4.5
E3 1 1.2 91.2 0.27 4.5
E4 5.6 75.3 0.23 2.4
C1 6.2 71.8 .20 2.3
C2 8.0 62.7 .12 4.6

 

 

a = Ground reaction force values normalized by body mass.
b = Knee extensor moment values normalized by body mass.

Note. E = experimental group.
C = control group.

187

Table 18

Pre-intervention Mean Values for the Dependent Variables of Each Subject during

Landing with Unanticipated Conditions

 

 

 

Subject Mean Peak Mean Peak Knee Mean Time to Mean Peak
Identification Ground F lexion Angular Peak Knee Right Knee
Reaction Force Displacement on F lexion Angular Extensor
on Impact” Impact (degrees) Displacement on Moment on
Impact (s) Impactb
E1 20.1 54.8 0.16 5.4
E2 18.9 57.3 0.20 4.0
E3 18.2 74.4 0.22 4.7
E4 15.3 70.7 0.19 4.0
Cl 13.5 72.3 0.19 3.8
C2 18.5 38.9 0.13 7.5
a = Ground reaction force values normalized by body mass.
b = Knee extensor moment values normalized by body mass.
Note. E = experimental group.
C = control group.

 

 

188

Table 19

Post Intervention Mean Values for the Dependent Variables of Each Subject during

Landing with Anticipated Conditions

 

 

 

Subject Mean Peak Mean Peak Knee Mean Time to Mean Peak
Identification Ground F lexion Angular Peak Knee Right Knee
Reaction Force Displacement on F lexion Angular Extensor
on Impact” Impact (degrees) Displacement on Moment on
Impact (3) Impactb
E1 9.4 70.9 0.19 2.3
E2 13.6 71.4 0.21 3.3
E3 19.2 74.0 0.19 4.1
E4 9.4 77.6 0.22 2.8
CI 7.2 64.3 0.21 2.3
C2 6.6 66.4 0.09 5.6
a = Ground reaction force values normalized by body mass.
b = Knee extensor moment values normalized by body mass.
Note. E = experimental group.
C = control group.

 

 

189

Table 20

Post Intervention Mean Values for the Dependent Variables of Each Subject during

Landing with Unanticipated Conditions

 

 

Subject Mean Peak Mean Peak Knee Mean Time to Mean Peak
Identification Ground F lexion Angular Peak Knee Right Knee
Reaction Force Displacement on F lexion Angular Extensor

on Impact“ Impact (degrees) Displacement on Moment on
Impact (3) Impactb
E1 24.3 47.9 0.14 6.8
E2 17.0 60.5 0.21 3.6
E3 26.7 80.4 0.27 5.1
E4 17.3 70.6 0.22 4.6
C1 17.0 58.0 0.18 4.1
C2 20.8 55.7 0.15 6.5

 

 

a = Ground reaction force values normalized by body mass.
b = Knee extensor moment values normalized by body mass.

Note. E = experimental group.

C = control group.

 

190

Table 21

Mean Peak Ground Reaction Force on Impact“

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials Trials

E1 9 20.1 7 24.3

E2 8 l 8.9 10 17.0

E3 4 1 8.2 3 26.7

E4 9 15.3 1 1 17.3

C1 10 13.5 9 17.0

C2 10 18.5 1 1 20.8

 

 

a = Ground reaction force values normalized by body mass.

Note. E = experimental group.

C = control group.

 

191

Table 22

Mean Peak Knee F lexion on Landing

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials (degrees) Trials (degrees)

E1 9 54.8 12 47.9

E2 8 57.3 1 1 60.5

E3 4 74.4 9 80.4

E4 9 70.7 1 1 70.6

C1 10 72.3 9 58.0

C2 10 38.9 12 55.7

 

 

Note. E = experimental group.

C = control group.

 

192

Table 23

Mean Time to Peak Knee F lexion on Impact

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials (seconds) Trials (seconds)

El 9 0.16 12 0.14

E2 8 0.20 1 1 0.21

E3 4 0.22 9 0.27

E4 9 0.19 1 1 0.22

CI 10 0.19 9 0.18

C2 10 0.13 12 0.15

 

 

Note. E = experimental group.

C = control group.

 

193

Table 24

Mean Peak Right Knee Extensor Moment”

 

 

 

 

Subject Number of Pre-intervention Number of Post intervention
Identification Trials (N—m) Trials (N-m)
E1 9 5.4 12 6.8
E2 8 4.0 10 3.6
E3 4 4.7 9 5.1
E4 9 4.0 l 1 4.6
C1 10 3.8 9 4.1
C2 10 7.5 12 6.5
a = Right knee extensor moment values normalized by body mass.
Note. E = experimental group.
C = control grga.

 

194

 

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