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This is to certify that the

dissertation entitled

A KINEMATIC ANALYSIS OF THE DEVELOPMENTAL
SEQUENCE OF KICKING USING A DIRECT
AND ANGLED APPROACH

presented by

Alfred Henry Bransdorfer

has been accepted towards fulfillment
of the requirements for

Ph.D. degree in KinesioIogx

 

WM LIX/«LA

Major professor

Datefif” 029i I???

MS U is an Affirmative Action/[q ual Opportunity Institution

 

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PLACE IN RETURN BOX
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To AVOID FINES return on or before date due.

 

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JUN 14 2005
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A KINEMATIC ANALYSIS OF THE DEVELOPMENTAL SEQUENCE
OF KICKING USING A DIRECT AND ANGLED APPROACH

By

Alfred Henry Bransdorfer

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Kinesiology

1998

ABSTRACT

A KINEMATIC ANALYSIS OF THE DEVELOPMENTAL SEQUENCE
OF KICKING USING A DIRECT AND ANGLED APPROACH

By

Alfred Henry Bransdorfer

The purpose of this study was to examine and quantify the developmental
sequence of kicking in children using direct and angled approaches to the ball. Twenty
children, ranging from three to eight years of age participated in the study and was
identified as one of the four classic stage levels of kicking development. Using the Aerial
Performance Analysis System (A.P.A.S.) the subjects were video taped while kicking a
standard youth size three soccer ball and the newly developed lightweight Micro-Soccer
ball. Angular displacements, velocities, and accelerations of the kicking limb were
calculated for data analysis.

Predicted trends were established for both approach types. Few of the predicted
characteristics were found for the direct approach, whereas, most of the predicted
characteristics were found for the angled approach. One major finding was knee flexion
at contact for all four stages with both ball types during both approaches.

A segmental relationship of the kicking limb, where the thigh of the kicking limb

decelerated as the shank accelerated at contact, was found in the stage four subjects as

predicted. Although not predicted, an elementary form of the segmental relationship was
also found in the stage three subjects.

Significant differences were found in the angular velocity of the shank and
angular acceleration of the thigh between stages three and four at contact. Significant
differences were also found in the angular velocity of the shank and angular acceleration
of the thigh at maximum forward movement of the kicking limb between stages three and
four. Although few significant differences were found in the angular velocities and
accelerations of the thigh, as well as the shank between stages three and four, observable
differences were evident in the graphs of the kicking sequences for selected stage three
and four subjects.

Differences between the direct and angled approaches were minimal. Only the
angular acceleration of the shank, at contact, was found to be significantly different
between stages three and four. This finding was likely due to the increased difficulty of
the angled approach, as the angular acceleration of the shank was lower for the angled
approach.

The Micro-Soccer ball was found to be significantly different in release than that
of the standard youth size three soccer ball. No significant differences were found
between the two approaches. If kicking performance is measured by ball velocity, the

Micro-Soccer ball did positively improve kicking performance.

Capyright by
Alfi'ed Henry Bransdorfer
1998

DEDICATION

To Mom and Dad.
You taught me to never give up!
and
To Trish, Erik and Beth.
Thank you will never be enough.
I love you.

ACKNOWLEDGEMENTS

I would like to thank all the children who participated in my study. Also a special
thanks goes out to all the parents who graciously gave their time to allow their children to
be involved in the study. I cannot say thank you enough to Dr. Steven Smith of Hope
College who’s continued prayers, encouragement and assistance were priceless during the
completion of this study. Also, thanks goes to Jo Ann Janes who’s assistance to graduate
students many times goes unnoticed.

I would like to thank committee members Dr. John Haubenstriker, Dr. Crystal
Branta, and Dr. Roger Haut for their time and effort. Finally, I would like to thank my
advisor and dissertation director, Dr. Dianne Ulibarri for her patience, persistence, and

encouragement throughout the course of my study at Michigan State.

vi

TABLE OF CONTENTS

LIST OF TABLES .................................................................................. vii
LIST OF FIGURES ................................................................................. ix
CHAPTER 1
INTRODUCTION ................................................................................... 1
Statement of the Problem .................................................................. 2
Purpose of the Study ....................................................................... 3
Need for the Study .......................................................................... 4
Research Hypotheses ....................................................................... 4
Kinematic Variables ....................................................................... 5
Predicted Developmental Trends (Direct Approach) .................................. 7
Predicted Developmental Trends (Angled Approach) ................................ 10
Hypotheses ................................................................................. 12
Limitations ................................................................................. 13
Definition of Terms ....................................................................... 14
CHAPTER 2
REVIEW OF LITERATURE ..................................................................... 16
Movement and Mechanics ................................................................ 16
Characteristics of Kicking ................................................................ 19
Sequence and Coordination of Segments ............................................... 23
Kinematics and Kinetics of Kicking .................................................... 25
Muscular Strength and Kicking .......................................................... 31
The Ball ..................................................................................... 34
Summary of Related Literature .......................................................... 36
CHAPTER 3
METHODS AND PROCEDURES .............................................................. 38
Sample ...................................................................................... 39
Subject Preparation ........................................................................ 4O
Anthropometric Measurements .................................................. 42
Inherent Problems and Accuracy of A.P.A.S ........................................... 43
Data Collection Procedures ............................................................... 45
Reference Frame .................................................................. 45

vii

Identification of Subjects and Trials ............................................ 47

Kicking Procedures ........................................................................ 48
Data Reduction ............................................................................. 49
Statistical Analysis ......................................................................... 51
Kinematic Variables .............................................................. 51
CHAPTER 4
RESULTS AND DISCUSSION ................................................................. 53
Kinematic variables ....................................................................... 54
Developmental Trends for the Direct Approach ..................................... 54
Preparatory Phase ................................................................ 55
Contact Phase ................................................................... 60
Follow Through Phase ........................................................... 7O
Developmental Trends for the Angled Approach ................................... 73
Preparatory Phase ............................................................... 74
Contact Phase ................................................................... 77
Follow Through Phase .......................................................... 83
Segment Timing and Coordination .................................................... 85
Segment Rotation Differences Between Stages Three and Four ................ 89
Direct Approach Versus Angled Approach .......................................... 103
Standard Youth Soccer Ball Versus the Micro-Soccer Ball ...................... 110
Post Filming Interview ................................................................ 113
Summary of Results .................................................................... 1 15
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS ........................................... 121
Recommendations ....................................................................... 134
LIST OF REFERENCES ........................................................................ 137
APPENDIX A .................................................................................... 141
APPENDIX C .................................................................................... 144

viii

LIST OF TABLES

Table 1 - Predicted Trends for the Direct Approach with Both a Standard Youth

Soccer Ball and a Micro-Soccer Ball .................................................. 9
Table 2 - Predicted Trends for the Angled Approach While Kicking a Standard Youth

Soccer Ball and a Micro-Soccer Ball ................................................ 12
Table 3 - Sample Population .......................................................................................... 40
Table 4 - Mean Hip and Knee Joint Angles (degrees) at Maximum Backswing for

Stages 1-4 .................................................................................. 56
Table 5 - Mean Hip and Knee Joint Angles (degrees) at Contact for Stages 1-4..... . . . . .61
Table 6 - Kinematic Variables for Subjects’ Stages 1-4 at Contact ......................... 65

Table 7 - Knee Joint Angles (degrees) from Contact to Maximum Forward
Movement for Stages 1-4 with a Standard Ball (Micro-Soccer Ball)..............71

Table 8 - Mean Hip and Knee Joint Angles (degrees) at Maximum Backswing for the
Basic and Mature Stages75

Table 9 - Basic and Mature Stage Knee and Hip Joint Angles (degrees) at Contact with
a Standard Youth Soccer Ball (Micro-Soccer Ball) ................................. 78

Table 10- Segment Velocity for Basic Stage Performers with a Standard Youth Soccer
Ball (Micro-Soccer Ball)80

Table 11- Velocity and Acceleration for Basic and Mature Stage Subjects at Contact
Using a Standard Youth Soccer Ball (Micro-Soccer Ball) ....................... 81

Table 12— ANOVA: Stage Effect on Mean Angular Velocity and Mean Angular
Acceleration for Stage Three and Four Subjects at Maximum Backswing. . ...91

Table 13- AN OVA: Stage Effect on Angular Velocity and Acceleration at
Contact ..................................................................................... 92

ix

Table 14- AN OVA Stage Effect on Angular Velocity and Acceleration at Maximum
Forward Movement... 94

Table 15- Angular Velocity and Acceleration Comparisons Between Stage Three and
F our ...................................................................................... 95

Table 16- AN OVA: Approach Effect on Angular Velocity and Angular
Acceleration for the Thigh and Shank at Maximum Backswing ................... 105

Table 17- AN OVA: Approach Effect on Angular Velocity and Angular
Acceleration for the Thigh and Shank at Contact ......................................... 106

Table 18- ANOVA: Approach Effect on Angular Velocity and Angular
Acceleration for the Thigh and Shank at Maximum Forward Movement 1.08

Table 19- Angular Velocity and Acceleration Comparisons Between the Direct and

Angled Approach ..................................................................... 109
Table 20- Initial Ball Velocities Using a Direct Approach................... . . 110
Table 21- Initial Ball Velocities Using an Angled Approach................................... 111
Table 22 - Analysis of Variance for Ball Velocity ........................................................ 112
Table 23- Exit Interview Questions and Subject Selections ......................................... .113

Table 24- Stage Level and Age of Subjects Who Thought the Standard Ball was
Easier to Kick .......................................................................... 1 14

Table 25- Stage Level and Age of Subjects Who Thought the Micro-Soccer ball
was Harder to Kick ................................................................... l 15

Table 26- Characteristics Found for the Direct Approach with a Standard
Youth/Micro-Soccer Ball ............................................................ 123

Table 27- Characteristics Found for an Angled Approach using a Standard
Youth/Micro-Soccer Ball ............................................................ 127

LIST OF FIGURES

Figure 1 - Test shorts ..................................................................................................... 41
Figure 2 - Target locations and order of digitization ...................................................... 42
Figure 3 - Calibration structure ...................................................................................... 46
Figure 4 - Test area setup ............................................................................................... 47
Figure 5 - Segment and joint angles. (a) Method for segment angle calculations.

(b) Joint angles used after segment angle calculations ........................... 50
Figure 6 - Mean hip and knee joint angles at maximum backswing, stages 1 - 4 .......... 56
Figure 7 - Knee and hip angles at maximum backswing for stages 1 - 4 .................... 59
Figure 8 - Mean hip and knee joint angles at contact, stages 1 - 4 ........................... 61

Figure 9 - Relationship at contact between the knee and hip joints during the direct
approach for stages 1 - 4 .............................................................. 63

Figure 10- Mean hip and knee joint angles at maximum forward movement, stages 1-4.7O

Figure l 1- Mean hip and knee joint angles at maximum backswing for Basic and
Mature Stages ......................................................................... 75

Figure 12- Hip and knee joint angles at maximum backswing for Basic and Mature
Stages .................................................................................. 76

Figure 13- Mean hip and knee joint angles at contact for Basic and MatUre Stages ....... 78

Figure 14- Basic and Mature Stage subjects’ thigh and shank angular velocities at
contact with the standard and Micro-Soccer balls ................................ 82

Figure 15- Mean hip and knee joint angles at maximum forward movement for Basic
and Mature Stages ..................................................................... 85

xi

Figure 16- Mature Stage performer shank and thigh relationship using a standard
youth soccer ball ....................................................................... 86

Figure 17- Mature Stage performer shank and thigh relationship using a Micro-Soccer
ball ....................................................................................... 86

Figure 18- Stage three performer using a direct approach while kicking a standard
youth soccer ball ..................................................................... 96

Figure 19- Stage four performer using a direct approach while kicking a standard
youth soccer ball ...................................................................... 96

Figure 20- Angular acceleration of the thigh and shank of a stage three performer
using a standard youth soccer ball ................................................ 100

Figure 21- Angular acceleration of the thigh and shank of a stage four performer
using a standard youth soccer ball ................................................ 100

xii

Chapter 1
INTRODUCTION

Soccer has been touted as the world's most popular game by countless proponents
of the game. As of 1996, in the United States alone, over three million youth under 19
years of age were registered to play soccer (Soccer Industry Council of America, 1996).
Soccer is a game of constant movement and adaptation, requiring teamwork and the use
of individual skills specific to the game. The individual soccer skills that must be
mastered include: dribbling, tackling, receiving, passing, heading, crossing and
shooting. For the aspiring soccer player, the development of these skills usually takes
place at an early age.

Kicking is an important aspect of the game and the development of an appropriate
motor pattern is crucial to success in soccer. Kicking has been described by Wickstrom
(1983) as a unique form of striking, in which the foot is used to impart force to a ball.
Studying the mechanics of sport specific skills (such as kicking) provides physical
educators and coaches with a deeper foundation to effect change in participants. By
investigating the kinematics associated with a developmental sequence of kicking, it is
possible to quantify previously observed characteristics.

Kicking has been described as a modification of bipedal locomotion by Huang,
Roberts and Youm (1982). These investigators differentiated between the locomotion
skills of walking and running and the skill of kicking because the primary force
production for a kick is from the swinging limb, not the support limb. They also stated
that the overall speed of the swinging distal segment was faster in kicking than in either

walking or running. The specific sequence and timing of the kick has been determined to
1

2
be valuable with respect to kicking performance (Putnam, 1983). Specific segmental

interactions have been identified in adults, as discussed by Putnam (1991, 1993) and
Glassow and Mortimer (1968), but have yet to be identified for the developmental years.
The qualitative descriptions by Haubenstricker, Seefeldt, Fountain and Sapp (1981)
provided an excellent basis for continuing to examine the skill of kicking. With an
increase of 279% in youth soccer participation in the United States since 1980 (Soccer
Industry Council, 1996), a demonstrated need for quantitative analyses of the
developmental sequence of kicking was highlighted. Quantitative analyses can aid in the
evolution and advancement of methods and strategies for teachers and coaches.

There have been numerous studies completed on kicking skills (Haubenstricker et
al., 1981), including segmental interactions (Barfield, 1995; Putnam, 1983, 1991 and
1993), muscular strength and coordination (Too and Hoshizaki, 1984), muscle activity
during a kick (DeProfi, Clarys, Bollens, Cabri and Dufour, 1988), and injuries associated
with kicking (Ekstrand and Gillquist, 1983; Nike, 1995). However, to date, few
investigators have studied the developmental aspects of kicking in soccer
biomechanically (Too and Hoshizaki, 1984; and Luhtanen, 1988).

Statement of the problem

Qualitative descriptions of kicking have been completed by Seefeldt and
Haubenstricker (1972) and Haubenstricker et al. (1981). They divided kicking into four
stages, or levels, which provide observable milestones during a child's development of
the kicking skill. The first two stages did not involve a moving approach to the ball,
whereas stages three and four involved a deliberate moving approach to the ball. The
stages of development provided teachers and coaches with a basis for improving the level
of performance that was age appropriate for children. Although this information was age

appropriate, it was not necessarily age dependent. The stages identified by

3
Haubenstricker et al. (1981) utilized a direct, sagittal plane approach to the ball, which

may or may not apply to an angled approach soccer kick.

With increased youth participation in soccer in the United States, a comprehensive
understanding of kicking is needed, as children begin to become involved in youth soccer
programs as early as four years of age (Soccer Industry Council of America, 1996).
Coaches and physical educators need to understand the mechanics involved in kicking in

order to utilize correct techniques with children in instructional settings.

Pmse of the study

Investigating the quantitative aspects of the development of kicking is important
to an increased understanding of kicking for improved teaching techniques and skill
development. Therefore, the purposes of this study were to:

1. Identify selected kinematic variables associated with children exhibiting
kicking stages one through four during a direct approach, using a standard size three
soccer ball and a newly developed light weight soccer ball.

2. Identify differences in selected kinematic variables associated with children
exhibiting kicking stages three and four using direct and angled approaches to the ball,
using a standard youth soccer ball and a newly developed lightweight soccer ball.

3. Identify the differences in the resultant ball velocity of a standard youth soccer
ball versus a lightweight soccer ball, when kicked by subjects exhibiting stages three and
four, for both the direct and angled approaches.

4. Identify the effect of a light weight ball on the motor development of kicking.
To date, no investigations have been found in which researchers studied the effects of ball

size, ball weight or ball color as these variables relate to kicking performance.

3 Need for the study

Quantitatively identifying characteristics associated with the development of
kicking will enable physical educators and coaches to deepen their understanding of the
qualitative descriptions existing in the literature. With this increased understanding of
kicking, the methods developed for teaching the skill of kicking will be more effective for
the participants. This study also broadened the knowledge base of kicking by identifying
the kinematic variables associated with the angled approach soccer kick. The
developmental stages of kicking, using the direct approach and angled approach, have not
been kinematically quantified for children. By quantifying observed phenomena, it is
possible to adapt current paradigms so that physical education teachers and youth sport
coaches can be more effective in assessing and improving the kicking performance of

children.

Research hypotheses

The current study investigated three major issues. First, this study investigated
selected kinematic variables for each of the four developmental stages of kicking using a
direct approach to the ball (Haubenstricker et al., 1981). Stage one was identified as the
least mature technique and stage four was identified as the most mature technique.
Secondly, this study examined differences in the selected kinematic variables in subjects
exhibiting stage three and four techniques, while utilizing an angled approach to the ball.
Finally, this study investigated the effect ball weight had on the selected kinematic
variables for each stage level, the approach used to kick the ball, and resultant ball
velocity. The best trial as defined by the identification of foot/ball contact, for each

soccer ball, was selected for analysis for all subjects using the direct approach. The best

5
trial as defined by the identification of foot/ball contact, for each soccer ball, was selected

for analysis for all subjects using the angled approach.

Kinematic variables

Standard videographic techniques were used to capture primarily sagittal plane

motion to obtain the following kinematic data:

1. The angular displacements of the thigh and shank segments at selected points during
the kick:
a. Stages one through four for the direct approach for both the standard size and
lightweight balls:
1) maximum backswing of the kicking leg,
2) foot and ball contact,
3) maximum forward movement of the kicking foot after the ball
leaves the foot.
b. Stages three and four for the angled approach for both the standard size and
lightweight balls:
1) maximum backswing of the kicking leg,
2) foot and ball contact,
3) maximum forward movement of the kicking foot after the ball
leaves the foot.
2. The angular velocities of the thigh and shank segments at selected points during the
kick:
a. Stages one through four for the direct approach for both the standard size and
lightweight balls:

1) maximum backswing of the kicking leg,

2) foot and ball contact,
3) maximum forward movement of the kicking foot after the ball
leaves the foot.
b. Stages three and four for the angled approach for both the standard size and
lightweight ball:
1) maximum backswing of the kicking leg,
2) foot and ball contact,
3) maximum forward movement of the kicking foot after the ball
leaves the foot.
3. The angular accelerations of the thigh and shank segments at selected points during
the kick:
a. Stages one through four for the direct approach for both the standard size and
light weight balls:
1) maximum backswing of the kicking leg,
2) foot and ball contact,
3) maximtun forward movement of the kicking foot after the ball
leaves the foot.
b. Stages three and four for the angled approach for both the standard size and
light weight balls:
1) maximum backswing of the kicking leg,
2) foot and ball contact,
3) maximum forward movement of the kicking foot after the ball
leaves the foot.
4. The resultant ball velocities of both the standard size and light weight soccer balls:
a. Stages one through four using the direct approach.

b. Stages three and four using the angled approach.

7
The developmental sequences of kicking have been described and validated in the

literature (Seefeldt and Haubenstricker, 1972; Haubenstricker et a1. ,1981). Based on
Seefeldt and Haubenstricker's and Haubenstricker's et a1. work, the following
developmental trends were predicted for the kicking leg of subjects involved in this

study.

Predicted developmental trends (direct approach)

1. Preparatory Phase. Predicted developmental trends for this phase will be:

a. The stage one performer will exhibit no hyperextension of the hip.

b. The stage two performer will exhibit both hyperextension of the hip and knee
flexion.

c. The stage three performer will exhibit greater hip hyperextension and knee
flexion than stage one and two performers, as a result of a deliberate approach to the ball.

d. A stage four performer will exhibit the greatest hip hyperextension and knee

flexion of all stages, as a result of the final approach step being an airborne phase or leap.

2. Force Production Phase (Contact). Predicted developmental trends for this phase will
be:

a. The stage one performer will displace the kicking leg forward as a result of hip
flexion causing the thigh to be positioned approximately parallel to the ground at ball
contact. The knee is flexed prior to and at ball contact.

b. The stage two performer will exhibit an increased angular displacement,
velocity and acceleration of the kicking leg, compared to stage one, resulting in increased
knee flexion during force production. The stage two performer will exhibit knee flexion

at ball contact.

8
c. The stage three performer will exhibit greater angular displacement, velocity

and acceleration of the kicking leg. At contact the knee will be slightly flexed.

d. The stage four performer will exhibit the greatest angular displacements,
velocities and accelerations of the kicking leg, and will have full knee extension at ball
contact. Additionally, the stage four performer will exhibit the segmental relationship
between the thigh and shank, in which the thigh velocity decreases as the shank velocity

increases to ball contact.

3. Follow through Phase. Predicted developmental trends for this phase will be:
a. The stage one performers will continue knee extension after ball contact.
b. The stage two performers will continue knee extension after ball contact.
c. The stage three performers will continue knee extension afier ball contact. .
There will be a continuing greater degree of knee extension from stage one to stage three.
d. The stage four performer will have complete knee extension and will be

airborne after ball contact.

An overview of the predicted trends for the direct approach were provided in
Table l. The chart of the characteristics also provided the reader a comparison across the

four stages.

Table 1

Predicted Trends for the Direct Approach \Mth Both a Standard Youth Soccer Ball and a
It: oocer

 

Stage 1

Prepartory
Phase

No hip hyperext.
Force
Production

Hip flexion

Parallel thigh

Knee flexion
Follow Knee extension
Through

9 = angular displacement
co = angular velocity
or = angular acceleration

Stage 2

Hip hyperext
Knee flexion

Shank angular
>9
>0)
>0

Thigh angular
>9
>0)
>(1

Knee
flexion
at contact

Knee extension

Stage 3

Step
>Hip hyperext.
>Knee flexion

Shank angular
>9

>0)
>0

Thigh angular
>9
>0)
>0.

Slight knee
flexion at

contact

Knee extension

Stage 4

Leap or hop
>Hip hyperext.
>Knee flexion

Shank angular
>9
>01
>(1

Thigh angular
>9
>0)
>or

Soccer paradox

Full knee
extension

Complete knee
extension
Airborne

 

Developmental trends for the gross motor skill of kicking have been presented

with subjects exhibiting a direct approach (Seefeldt & Haubenstricker, 1972;

10
Haubenstricker et al., 1981). However, to date, no literature has been found on the

developmental stages of kicking using an angled approach. A stage one or two performer
using a direct approach was not expected to be capable of performing an angled approach,
since these two stages do not have a deliberate approach to the ball. It was proposed that
the use of an angled approach would require performers to exhibit a relatively mature
developmental level (stage three or four) of kicking in order to successfully complete a
kick utilizing an angled approach. Since stages three and four used a deliberate approach
to the ball, it was expected that they could perform an angled approach kick. The
performer was required to approach the ball from an angle of 45 degrees rather than from
straight behind the ball as in a direct approach.

Predicted developmental trends (angled approach)

Based on the current literature and two preliminary investigations, the author
proposed two developmental stages for an angled kick, the Basic Stage and the Mature
Stage. The Basic Stage was the elementary level of the angled kick and was expected to
be seen in a performer who could exhibit a stage three direct approach kick. Therefore,
the stage three subjects were identified as Basic Stage subjects. The Mature Stage was
the more advanced stage of the angled kick and therefore, the stage four subjects were
identified as Mature Stage subjects. Based on related literature and the extensive soccer
background of the author, the following developmental trends were predicted for subjects

using an angled approach.

1. Preparatory Phase. Predicted developmental trends for this phase will be:

a. The Basic Stage performers will exhibit hip hyperextension and knee flexion of
the kicking leg as a result of a deliberate, angled approach to the ball. The support foot of
the non-kicking leg will be directed along the angled approach path.

11
b. The Mature Stage performers will exhibit a marked increase in hip

hyperextension and knee flexion as a result of an airborne leap prior to ball contact. The
support foot of the non-kicking leg will be placed parallel to the line of intended direction
the ball is to be kicked.

2. Force Production Phase (Contact). Predicted developmental trends for this phase will
be:

a. The Basic Stage performers will exhibit an increase in thigh and shank velocity
up to ball contact. At ball contact there will be knee flexion as well as hip flexion.

b. The Mature Stage performers will exhibit the relationship between the thigh
and shank characterizing the "soccer paradox". With the soccer paradox, the thigh
velocity will decrease as the shank increases in velocity. At ball contact the knee will be

in a flexed position.

3. Follow Through Phase. Predicted developmental trends for this phase will be:
a. The Basic Stage performers will maintain flexion at the knee joint of the
kicking leg.
b. The Mature Stage performers will exhibit marked flexion of the hip

accompanied by knee flexion during follow through.

An overview of the predicted trends for the angled approach were listed in Table 2.

12

 

 

Table 2
Predicted Trends for the Anlpled Approach While Kicking a SQndard Youth Soccer
a an a re r a

Preparatory Basic Stage Mature Stage

Phase
Step Leap
Hip hyperext. >Hip hyperext.
Knee flexion >Knee flexion
Support foot along approach Support foot H to intended direction
path

Force

Production
Increasing thigh and shank velocity Thigh velocity decrease
Hip flexion Shank velocity increase
Knee flexion Knee flexion

Follow

Through
Knee flexion >Hip flexion

Knee flexion
m

From the current literature and predicted trends, the following hypotheses were

developed. Each of the hypotheses were tested within the context of this study.

1. Each of the kinematic variables will follow the predicted trends as stated.

The kinematic variables include the angular displacements, velocities, and
accelerations of the thigh and shank at three distinct positions during the kick. These
positions were: a) maximum backswing of the kicking leg, b) foot/ball contact and c)

maximum forward movement of the kicking foot after the ball leaves the foot.

13
These kinematic variables were expected to follow the predicted trends, for each

stage of the direct approach and the angled approach as defined for the preparatory, force

production (contact), and follow through phases.

2. There will be a difference in the rotations of the thigh, as well as the shank, of the
kicking limb between subjects exhibiting stages three and four while using a standard
youth soccer ball using a direct approach to the ball. The stage four subjects will exhibit
a more mature pattern of the kicking limb than the stage three subjects, as rotation of the
thigh will be greater in the initial portion of the force production phase, with minimal
rotation of the shank about the knee joint. In the later portion of stage four’s force

production phase, thigh rotation will decrease as shank rotation increases to ball contact.

3. There will be a difference in the rotations of the thigh, as well as the shank, of the

kicking limb of the subjects using a direct approach when compared with subjects using

an angled approach, while kicking a standard youth soccer ball.

4. The resultant ball velocity of the light weight soccer ball will be greater than that of
the standard youth soccer ball, regardless of approach.

Limitations

The following limitations were identified for this study:
1. The subject's ability to kick the soccer balls forcefully as instructed by the
investigator.
2. The ability to see all targets throughout the digitization process. Targets that were

hidden by body parts during part of the kick were digitized using a “best guess”.

14
3. The APAS system is capable of filming only at .017 sec/flame. This relatively low

speed may cause any fine tuning of data point capture to be missed, since it physically
was not captured.

4. The software used by the APAS system. Since the data are stored in binary, the 3-D
data points could not be downloaded in order to use our own sofiware programs for

calculations. These limitations were discussed at more length in Chapter three.

Definition of terms

Acceleration - The rate of change of velocity.

Anthropometry - Measurements of the human body including the size, shape and weight
of body segments.

Displacement - A change in position.

Extension - The movement of a segment, relative to an adjacent segment, in which the
angle increases between the segments.

FIFA - The Federation Internationale de Football Association, the world governing body
of international soccer.

Flexion - The movement of a segment, relative to an adjacent segment, in which the angle
decreases between the segments.

Kinematics - Description of movement including time, displacement, velocity and
acceleration.

Soccer instep kick - The type of kick in which a soccer ball is contacted on the instep of
the kicking foot (lace area on the shoe).

Support foot - The foot providing support for the body during the kicking action.
Velocity - The rate of change of displacement.

MBS - Maximum backswing. The maximum posterior position of the kicking leg thigh.
FBC - Foot/Ball Contact.

15
MF M - Maxirmun forward movement. The maximum height of the kicking leg foot from

the floor.
9 (Theta) - Angular displacement. The angular displacement was determined as the angle
between two adjacent segments.

(0 (Omega) - Angular velocity. 0) = A9 / At.

or (Alpha) - Angular acceleration. or = Am / At.

Chapter 2
REVIEW OF LITERATURE

The purpose of this review was to examine the literature related to selected
variables that affect the performance of a soccer kick in children. A major goal of this
research was to identify the differences in the kinematic variables associated with the
development of kicking in children. Therefore it was necessary to examine the literature
pertaining to the developmental and mechanical characteristics of kicking. This
information provided a foundation for discussion as it related to the development of

kicking in children.

Movement and mechanics

Mechanics is the branch of physics that investigates the influence of forces on
bodies and mechanical systems (Hall, 1995). Biomechanics is defined as the science that
studies the mechanics of human motion (Hall, 1995). "Motor development is the
progressive change in motor behavior throughout the life cycle, brought about by
interaction among the requirements of the task, the biology of the individual, and the
conditions of the environment” (Gallahue and Ozrnun, 1995, p. 3). In combination, it is
possible to use biomechanical principles and techniques to study the development of
motor skills. It was not the intent of this author to provide an exhaustive review on the
discipline of Motor Development but rather an overview to justify quantification of the
qualitative analysis of the fundamental motor skill of kicking as reported by Seefeldt and

Haubenstricker (1972) and its subsequent validation by Haubenstricker et al. (1981).
16

17
Development of motor skills is evidenced by changes in the movement patterns of

the skills. It is possible to observe the changes in movement behavior by observing the
process (form) and product (performance) (Gallahue and Ozmun, 1995). Observable
movements have been grouped into three categories: stabilizing movements, locomotor
movements, and manipulative movements. It is likely that some movements may contain
a combination of all three categories (Gallahue and Ozmun, 1995). Playing soccer
involves all three types of movements, as does kicking a ball. The approach to the ball
requires locomotor skill, the contact of the support foot with the ground stabilizes the
individual in order to kick (manipulate) the ball. By dividing a motor skill into phases, a
foundation for specific sequential descriptions of a motor skill is established.

Qualitative analyses, such as the studies completed by Seefeldt and
Haubenstricker (1972) and Haubenstricker et a1. (1981) provided information on the
process or form of the development of kicking. The use of biomechanical techniques in
studying the stages of development can provide a method by which the skill can be
quantified and further describe the development of kicking. Biomechanics can provide
the physical educator with a means to apply mechanical principles to the analysis of a
fundamental motor skill such as kicking. A mechanical analysis of kicking can serve as a
standard and make it possible to understand kicking beyond the descriptive level
(Wickstrom, 1983). Additionally, it is possible to study the development of kicking as it
becomes "biomechanically more efficient" (Wickstrom, 1983, p. 17). A biomechanical
analysis of kicking can highlight the relative importance of muscular strength in the
development of this fundamental motor skill. Although muscular strength was not a
variable studied in the present investigation, it is worthy to note its importance in the
development of a motor pattern.

Force is required to produce movement. A component of that force is muscular
strength, as well as the coordinated movement for maximum summation of forces. To

execute a mature form of a motor skill, the muscles must provide enough force to start,

18
accelerate, stop or change the direction of movement effectively, according to a

prescribed pattern (Wickstrom, 1983). A lack of force due to inadequate muscular
strength can dictate the form and limit performance. In velocity oriented skills, such as
kicking, inadequate muscular strength is manifested in a reduced velocity of the kicking
segments or limbs affecting the process, as well as the resultant velocity of the ball or
product. "Velocity production is an essential consideration in most fundamental motor
skills" (Wickstrom, 1983, p. 18). Other things being equal (i.e., size, weight, strength), a
subject exhibiting a stage one kick should exhibit a lower velocity of the swinging
(kicking) limb, than a stage four performer. Consequently, a lower velocity of the
swinging limb results in a lower resultant velocity of the ball as it comes off the foot.

By using biomechanical procedures it is possible to study the mechanics of
kicking and other fundamental motor skills, as was evident in the study by Kiger (1987).
The purpose of Kiger's study was to identify specific mechanical differences observed in
the development of the skill of nmning and to identify which specific kinematic variables
differed between the stages and between gender. Limited statistical significance was
obtained (which could be attributed to a small sample size and p value) in the study for
stage effect, but Kiger found developmental trends across the stages. The work by Kiger
(1987), and the theories developed by Wickstrom (1983) and Gallahue and Ozrnun
(1995) influenced the current author's decision to use a biomechanical approach to
capture and analyze the data. Subsequent digitization of the data and software useage
allowed the data to be quantified. A biomechanical evaluation of the developmental
stages of kicking, qualitatively studied by Seefeldt and Haubenstricker (1972) and
Haubenstricker et al. (1981), was performed. In addition, the description and

quantification of the development of a diagonal kick was performed by the author.

1 9
Characteristics of kicking

Kicking is a basic skill that is used in various activities and sports. Kicking has
been described as a modification of walking and running (Huang et al., 1982). The main
difference between walking, running, and kicking is in the primary force production.
During a kick, the force production is in the swinging segment, whereas in walking, force
is produced in the support segment. Huang et al.(1982), in a biomechanical analysis,
determined that the speed of the swinging segment is significantly faster in a kick than in
running. Kicking has been divided into preparatory, force production andfolfiloflw through
phases (Haubenstricker et al., 1981). As a child improves in this particular movement Ni
task, an orderly sequential progression of change occurs in movement control.
Biomechanically, ball contact is identified as an event that occurs behveerr the end of the
force production phase ”and the beginning of the follow through phase. A specific
se‘qwue‘nc-eaofjrfro’ve’ments and timing are requirements for a successful kick. Also,
appropriate levels‘oimtu’spularfistrfl'efingthare-”required to" propel an object, such as a soccer

ball. A soccer kick using the right leg has been described in the following manner by
Douge (1988):

I 45 degree approach with a slight forward lean;

II leg adduction of the kicking leg on the second to last step to cater
for trunk rotation;

III explosive final step;
IV externally rotate the non-kicking hip;

V support foot 15-20 cm to the side of the ball, transverse arch
crosses an imaginary ball bisection;

VI internally rotate the kicking leg during the kick: Trunk rotation
begins simultaneously with kicking leg hip extension and
knee flexion;

VII support leg knee eccentric contraction to absorb body weight;

20
VIII kicking leg knee leads foot to ball;

IX as kicking leg passes over ball, it is forcefully extended and foot
plantar flexed; the lefi arm adducts across the chest to prevent
excessive left shoulder rotation and keeps the shoulder parallel
to the goal line;

X deceleration by eccentric knee flexion, external rotation,
extension and abduction at the hip joint of the kicking leg.

The skill as described above can be difficult for children to execute with a
stationary ball, let alone a moving ball, as is often the case in a soccer game. A child
trying to kick a ball must appropriately sequence the body segments in order to produce
the desired outcome of kicking a ball. Keough and Sugden (1985), explained that
children have three general problems they must solve when striking (kicking) an object.
First, they must control the sequence of the limb movement. Second, they must direct the
limb to a position that will contact the object in the appropriate direction. Thirdly, they
must time the sequence to end afier impact. Potentially there is a fourth problem of force
production modulation. Force production modulation adds a muscular strength
component for the child attempting to propel the ball in a specific direction and over a
given distance. Therefore, a rather complex combination of coordination and muscular
strength is required in performing a successful kick.

A developmental sequence of kicking (Haubenstricker et al., 1981) is helpful in
assessing performance qualitatively. The developmental sequence used by the Motor
Deve10pment Program at Michigan State University (MSU) was divided into four stages
with a specific description of the three phases within each stage. The current study
determined if the selected kinematic variables of linear and angular displacements,
velocities and accelerations differed between the stages, for subjects who used a standard
youth soccer ball and a newly developed lightweight ball. The characteristics from
Haubenstricker's et al. (1981) developmental sequence of kicking of stage one through

four follow:

Stage 1

Stage 2

Stage 3

Stage 4

21

ngaratog Phase - The performer is usually stationary and
positioned near the ball. If the performer moves prior to kicking,

the steps are short and concerned with spatial relationships rather than
obtaining momentum for the kick.

Force Production - The thigh of the kicking leg moves forward with the
knee flexed and is nearly parallel to the surface by the time the foot
contacts the ball. Knee joint extension occurs after contact, resulting in
pushing rather than a striking action. Upper extremity action is usually
bilateral, but may show some opposition in older performers. (If the
performer is too far from the ball as the extremity moves to meet the ball
the knee flexes only slightly and the leg swings forward from the hip in a
pushing action.)

Follow Through Phase - The knee of the kicking leg continues to extend
until it approaches 180 degrees. If the trunk is inclined forward following
contact with the ball, the performer will step forward to regain balance. If
the trunk is leaning backward, the kicking leg will move backward after
ball contact to achieve body balance.

Preparatog Phase - The performer is stationary. Initial action involves
hyperextension at the hips and flexion at the knee so that the thigh of the
kicking leg is behind the mid-frontal plane. The arms may move into
position of opposition in situations of extreme hyperextension at the hips.

Force Production Phase - The kicking leg moves forward with the knee
joint in a flexed position. Knee joint extension begins just prior to foot
contact with the ball. Arm-leg opposition occurs during the kick.

Follow Through Phase - Knee extension continues after the ball leaves the
foot, but the force of the kick usually is not suflicient to move the body
forward. Instead, the performer usually steps sideward or backward.

Preparatog Phase - The performer takes one or more deliberate steps to
approach the ball. The support leg is placed near the ball and slightly to
the side of it.

Force Production Phase - The kicking foot stays near the surface as it
approaches the ball. The trunk remains nearly upright, thereby preventing
maximum force production. The knee begins to extend prior to contact.
Arm-leg opposition is evident.

Follow Through Phase - The force of the kick may carry the performer
past the point of contact if the approach was vigorous. Otherwise the
performer may remain near the point of contact.

Preparatog Phase - The approach involves one or more steps with the
final "step" being an airborne run or leap. This permits hyperextension of
the hip and flexion of the knee.

Force Production Phase - The shoulders are retracted and the trunk is
inclined backward as the supporting leg makes contact with surface and
the kicking leg begins to move forward. The movement of the thigh

22

nearly stops as the knee joint begins to extend rapidly just prior to contact
With the ball. Arm-leg opposition is present, as in the previous two stages.

Follow Through Phase - If the forward momentum of the kick is sufficient,
the performer either hops on the support leg or scissors the legs while
airborne in order to land on the kicking foot.

The influence of age, gender, balance, and participation in organized soccer
programs on the development of kicking by children in grades K - 8 was completed by
Butterfield and Loovis (1994). Seven hundred and sixteen boys and girls in grades K-8
were studied. The children were tested individually in kicking performance, static
balance, dynamic balance, and were given a survey to determine youth soccer
participation. Butterfield and Loovis (1994) reported that boys' kicking performance
increased linearly on a yearly basis through grade four, dropped off in grade five,
recovered in grade 6, and dropped off in grades seven and eight. The percentage of girls
exhibiting a mature pattern was lower than that of the boys, but the development of
kicking paralleled the boys’ results.

The grade four decrement could have resulted from children choosing other
activities to be involved in that did not involve kicking. Gallahue (1982) has termed
grade four a "sport-related" stage of motor development. It is this age when children
begin to increase their involvement in specific sports.

Participation in organized soccer did not influence the development of a mature
kicking pattern (Butterfield and Loovis, 1994). It was hypothesized that youth sports
programs may provide excellent sources of exercise but do not influence skill
development. Butterfield and Loovis (1994) indicated that some children do not develop
a mature pattern even by grade eight. This trend highlighted the need to continue
emphasizing skill development, as well as encouraging participation in youth sports.

Putnam (1983) examined the interaction between the thigh and shank during a
punt kick. Putnam determined that the motion of the thigh influenced the shank by

angularly accelerating it in the positive direction during the kick. During the initial phase

23
of a kick, the thigh dominated, with little rotation of the shank relative to the thigh.

During the remainder of the kick, the rotation of the thigh decreased rapidly while
rotation of the shank increased. This relationship was important in analyzing a kick. A
decrease in thigh rotation has been seen in skilled kickers (Barfield, 1995; Putnam, 1983
and 1991; T00 and Hoshizaki, 1984; Plagenhoef, 1971) and was qualitatively described
in the stage four of the MSU developmental sequence (Haubenstricker et al., 1981). Too
and Hoshizaki (1984) and Plagenhoef (1971) also determined that there was a sequenced

relationship evident in skilled performers.

Sequence a_n_d coordination of segments

The body segments involved in kicking can be modeled as an open-linked system
(Huang et al., 1988; Putnam, 1993), where the segments are rigid bodies of which the
distal segment moves freely through space. In a kick, the most distal end of the system is
used to impact an object. The sequence of the kicking motion can be characterized as
progressing from proximal to distal (Putnam, 1983, 1991 and 1993; Haubenstricker et al,
1981; Plagenhoef, 1971).

Bunn (1972) stated that to maximize the speed at the distal end of a linked system,
the movement should start with the more proximal segment and progress to the more
distal segments. Each distal segment then starts its motion at the instant of greatest speed
of the preceding segment. This movement has been called the summation of speed and
summation of forces principle. According to Putnam (1993) the summation of forces
principle was of limited value in describing a kick because of the lack of mechanical
explanation. The use of the summation of forces principle suggested that at the end of the
movement, the speed of the distal end of the segment would have reached its maximal
linear and angular velocities at impact. Putnam stated that a segment’s endpoint resultant

movement did not explain the relative contributions of that segment. Plagenhoef (1971)

24
also utilized the summation of forces principle to determine a resultant linear velocity in

describing kicking performance.

Putnam (1993) compared the summation of speed principle, the use of joint
angular velocity, and the use of segment angular velocity while describing a kick. She
described the use of joint angular velocity as most valuable when examining the most
proximal segment participating in the sequence, and the angular velocities of the joints as
most valuable when looking at the proximal ends of the remaining segments. Putnam
(1993) suggested that the use of joint angular velocities would be useful in visually
describing the motion of a kick.

The use of segment angular velocity data provided information to describe what
caused the motion of each segment of a kick (Putnam,l993). Putnam (1993) stated that
using segment angular velocities required knowledge of segment orientations, segment
angular accelerations and linear accelerations of the proximal end of the linked system.
Putnam also suggested that if one looked only at the distal segment's maximum speed,
one would sense that all the joints involved during a kick would be fully extended and the
angular rotations of the segments would be the same at the moment of impact.

Angular rotations of the thigh and shank segments were not the same at impact in
a soccer kick (Barfield, 1993; Putnam, 1983; Luthanen, 1988; Isokaw and Lees, 1988). It
has been determined that the angular rotation of the thigh was greater than that of the
shank during the force production phase of a kick. In actuality, as hip flexion began the
shank was rotating backward relative to the thigh. The backward rotation of the shank
resulted in flexion of the knee. As the kick progressed, the rotation of the thigh
decreased, while the forward rotation of the shank increased as described by Putnam
(1983). The decrease in the thigh's angular velocity did not result in acceleration of the
shank, but rather the decrease in thigh angular velocity was the result of the shank's
angular motion on the thigh according to Putnam (1983).

 

25
As a result of practice there are changes in the movement pattern of a soccer kick

that can be kinematically observed (Anderson and Sidaway, 1994). Anderson and
Sidaway (1994) examined the changes in coordination that resulted from practicing a
soccer kick by college age subjects. Their hypothesis was that the subjects would
initially simplify the control of the movement by limiting the range of motion of the hip
and knee joints. They also predicted that over time, and with supervised practice, the
limitations on the range of motion would be removed. The subjects in the study were told
that their primary purpose was to try to maximize the ball velocity while hitting the target
area. Paired t tests were used to compare pre- to post practice results in the dependent
variables. The dependent variables, of interest to the current study, were maximum linear
foot velocity, maximum hip and knee angular velocity, and joint range of motion at the
hip and knee between the maximum and minimum angles at each joint. According to
Anderson and Sidaway (1994), all of the dependent variables of the study were related to
performance. Additionally, the authors determined there was an increase in performance

as a result of practice.

Kinematics and kinetics of kicking

Literature pertaining to the kinematic and kinetic variables of kicking has been
primarily concerned with resultant ball velocity as the measure of kicking performance,
with the majority of these studies using adults as subjects (Abo-Abdo, 1981; Barfield,
1995). A study by T00 and Hoshizaki (1984) investigated the contribution of strength
and coordination patterns to kicking performance. T00 and Hoshizaki (1984) used two
mini-soccer balls weighing 347 and 349 grams, for the 9-12 year-old subjects. The effect
of the mini-soccer ball on mechanical variables of the kick was not determined. Too and
Hoshizaki (1984) studied the relationship between isokinetic quadriceps leg strength and

ball angle projection, ball lateral deviation, and kicking leg movement patterns on

 

26
maximal distance a ball was kicked. The study involved subjects 9-17 years of age. The

subjects were divided into three age groups: 9-12 years, 13-15 years and 16-17 years.
The 9-12 year old group used a mini-soccer ball, whereas the other two groups used a
standard size five ball. The results of T00 and Hoshizaki (1984) indicated that ball angle
of projection varied the most for the 9-12 year old group, relative to the three groups.
The 13-15 year old group had the greatest variation in linear ball velocity, while the 16-
17 year old group varied in isokinetic impulse at 30 degrees/sec, relative to the three
groups . The authors indicated that all of the subjects had mature kicking patterns, as
exhibited in a decrease in thigh angular velocity with a corresponding increase in shank
velocity prior to ball-foot contact. Too and Hoshizaki stated that foot velocity at impact
was related to leg strength and direction applied through the ball was related to motor
coordination. Too and Hoshizaki suggested that strength training was more important
for the 13-17 years of age group, whereas for the 9-12 years of age group, proper
technique should be emphasized.

Resultant ball velocity has been used by many investigators to measure the
performance level of subjects completing a kick. The velocity of the ball provided the
researcher with a measure of the product of the process of kicking. Luhtanen (1988)
investigated resultant ball velocity during a maximal instep kick in soccer players 9-18
years of age. The authors examined the resultant forces and their moments at the hip,
knee and ankle joint of the kicking leg as determined from 2-D cinematography and
subsequent calculations. Ground reaction forces of the support leg were also determined.
The subjects in the study were divided into three groups (9-11, 12-14 and 15-18 years of
age). Ball velocities obtained for each group during the study were 14.9, 18.4 and 22.2
m/sec respectively. A one-way AN OVA was used to assess differences between the
groups in angular velocity and acceleration of the thigh and shank. Angular velocity and
acceleration were determined to be significantly different between the groups, whereas

timing and maximum angular velocity were not, also assessed via a one-way AN OVA.

 

27
There were minimal differences in the patterns for the three groups. Luhtanen (1988)

indicated that the primary difference between the groups was in the magnitude of force
production. A 450 gram ball was used for all subjects in Luhtanen’s study. The specific
weights and dimensions of soccer balls were discussed later in this chapter.

Few studies have investigated the kinematics and kinetics of a soccer kick in
children (Luhtanen, 1988; Too and Hoshizaki, 1988). Therefore it was necessary to
review literature pertaining to older subjects completing a soccer kick in order to fully
understand current theories.

The sequence or timing of the segments is valuable in assessing the performance
of a kick, regardless of the type of kick that is performed (Putnam, 1983). Muewssen and
Tant (1992) studied the timing, sequence, and interaction of the segments of the leg
associated with the soccer instep kick used during low drive, high drive, and maximum
distance kicks in college age men. The resultant ball velocities were 21.17, 14.14 and
21.15 m/sec, respectively. Muewssen and Tant (1992) determined that pelvic rotation,
hip flexion and extension, and knee flexion and extension were greatest during the high
drive kick. The maximum distance and low drive kicks resulted in the greatest hip
abduction/adduction. The temporal pattern of the three kicks were very similar.
Differences in maximum angular velocity of the lower leg were determined to be
significant between the high drive and maximum distance kicks. Muewssen and Tant
determined that the pelvis and the thigh moved forward as the lower leg began its
posterior rotation. Prior to ball contact, the pelvis and thigh decreased in velocity as the
lower leg increased in velocity. No significant differences were found between the
angular velocities of the segments during each of the three kicks. Significance was found
between the maximum angular velocity of the lower leg and the high drive and maximum
distance kicks. The authors concluded that the timing between the three types of kicks
were similar, providing evidence that hip abduction/adduction and maximum angular

velocity of the lower leg were related to ball velocity.

 

28
The ability to kick equally well with the dominant and non-dominant limb is also

an important quality for a soccer player. Barfield (1995) studied the kinematic and
kinetic differences between dominant and non-dominant limbs during a soccer in-step
kick. Barfield found significant differences between limbs of college-age varsity soccer
players. Barfield isolated the period of support foot contact through ball contact of the
striking limb for analysis. The study correlated maximum ball velocity with kinematic
and kinetic variables obtained. The kinematic variables that were found to be highly
correlated were: maximum linear velocity of the toe, linear velocity of the toe at ball
contact, linear velocity of the ankle at ball contact, mean value fiom support foot contact
to ball contact for linear velocity of the toe and mean value from support foot contact to
ball contact for linear acceleration of the knee. Barfield (1995) pointed out that although
angular velocity of the knee did not correlate with ball velocity, maximum angular
velocity of the knee did occur approximately at ball contact in the dominant limb.
However, maximum angular velocity of the knee did not occur at contact, rather it
occurred following contact for the non-dominant limb.

The angle at which a ball is approached during a kick has an influence on ball
velocity. An approach angle of 30 to 60 degrees produced the greatest ball velocity
(Isokaw and Lees, 1988). Plagenhoef (1971) also showed that the approach angle was
significant in maximum ball velocity. The study by Isokaw and Lees (1988) determined
kinematic and kinetic variables with approach angles to the ball fi'om zero to 90 degrees.
The study used a one step approach, in contrast to the two step approach used in
Barfield's (1995) study. The differences in a kick with a one step approach and two step
kick have not been specifically studied. Isokaw and Lees (1988) did state: "There might
be two kicking patterns in the performance of the instep kick with one step."(p. 454) This
statement may be a factor when applying the data of Isokawa and Lees to studies using a
two step approach, as different patterns of movement may exist during different types of

approaches and kicks. The importance of an angled approach can be qualitatively

 

29
appreciated while watching college or professional football place kickers, as the straight

on toe kick is rarely seen.

A 45 degree approach angle to the ball was found to be optimal for maximizing
ball velocity (Isokawa & Lees ,1988). Also, an approach angle of 45 to 60 degrees
balanced the body’s motion, due to the active torque produced during the kicking
movement. They suggested that an angled approach may reduce injury by reducing the
torque applied to the support foot, and thereby to the ankle and knee.

The type of approach to the ball is an important variable in a soccer kick.
Opavsky (1988) studied a standing and a running approach to the soccer kick. The study
was a descriptive study of the linear and angular kinematics of the foot, lower leg, upper
leg, combined lower leg and foot, and the whole leg. The data presented were consistent
with those of Barfield (1995) and Isokaw and Lees (1988). Opavsky (1988) did theorize
that the standing kick required more muscular force than the running kick, a result of
factoring out the body’s momentum. Maximum ball velocity was reported to be 23.48
m/sec for the standing kick and 30.78 m/sec for the running approach. These velocities
should not be surprising, since during a running kick a subject could benefit from the
body’s momentum of the kicking system.

Variability in skill level is evident across age and gender (Butterfield and Loovis,
1994). Consistency in performance, related to both process and product, is crucial for
elite performance and is desired at all levels of competition. Phillips (1985) studied the
variance exhibited between two kickers. One subject was a place kicker for a
professional football team and the other subject, a club level soccer player. The club
player exhibited more variability across trials than did the place kicker. Two issues were
raised with Phillips' study. First, the study should have used two place kickers or two
soccer players. One would expect differences to exist between a place kicker and a
soccer player. Kicking a soccer ball during a soccer match is variable, and highly

dependent upon the situation. Secondly, place kickers are instructed to kick the ball in

 

30
the same manner regardless of the distance. It is to be expected that the place kicker’s

approach to the ball is more consistent than that of the soccer player. Studying invariance
of elite kicking performance may be more effectively studied by using similar subjects.

There is a gradual increase in the segmental velocity as a kick moves through its
phases (Plagenhoef, 1971; Robertson & Mosher, 1983). As a kick progresses, the initial
acceleration is caused by hip flexors and deceleration is caused by the eccentric
contraction of the hip extensors (Roberston & Mosher, 1983). This work by Roberston
and Mosher supported the summation of muscle forces theory.

The specific sequences of kicking have been modeled, and specific variables have
been determined to describe those sequences (Putnam, 1991). Putnam examined the
interactive moments, resultant joint moments, and net moments during kicking, walking,
and running, as determined fi'om high speed film data and subsequent biomechanical
analyses. The discussion of resultant joint moments further explained observed segment
motions. Putnam did not agree with Robertson and Mosher (1983) who used the
summation of force principle to explain a kick. According to Putnam (1991), there was
no evidence that the forward swinging of the lower leg of a kick was initiated by the
larger muscles and continued by smaller muscles. Putnam (1991) stated: "changes in the
motion of any one segment within a system of linked segments cannot be attributed
solely to the muscle forces acting on that segment"(p. 140). The relationship of the
muscle forces and the segment motion was dependent upon the interaction between
adjacent segments. This relationship aids in explaining that a proximal-to-distal sequence
may not always follow a smnmation of muscle forces. Putnam (1991) discussed the role
the muscles play in producing sequential motion as difficult. The resultant joint moments
contributed to the net moments of the segments, counteracting the interactive moments.
This relationship was seen during the slowing of the thigh velocity as the lower leg

extended at the knee to make ball contact. Putnam did not quantify the role of the

 

31
muscles because of the non-linear relationship between the resultant joint moments and

the segment motions.

Zernicke and Roberts (1978) completed a study on leg forces and torques during a
kick. They found that during fast kicks, hip torques were small during the later phases of
the activity which supported Putnam’s (1991) work. The study highlighted the fact that
hip extensor moments either were not present or were small. The minimal magnitude of
the hip extensor moments helped to explain the influence of the shank on the motion of

the thigh, as the shank's movement forward caused the thigh to rotate backward.

Muscular strength and kicking

The relationship between muscular strength and human performance has been
investigated in most sports and has been found to be somewhat controversial. These
findings are also true for the soccer kick. Some theorists believed that muscular strength
training was critical to improved kicking performance (Cabri, DeProfi, Dufour & Clarys,
1988; DeProft, Cabri, Dufour & Clarys, 1988; Narici, Sirtori & Mognoni, 1988) as
measured by maximum ball velocity and maximum distance kicked; while others placed
emphasis on technical development (McLean & Tmnilty, 1993). When the component of
accuracy was added, muscular strength may not have been the primary factor in
performance (McLean & Tumilty, 1993). No studies have been completed investigating
the relationship of muscular strength and kicking development in children. Strength has
been suggested as a prerequisite for kicking a ball forcefully in adults. Strength could be
a factor in skill development in children but that determination was beyond the scope of
the current study. It was noteworthy to review the relationship between strength and
kicking in older subjects to provide a foundation for discussion as it related to the current

study.

 

32
Leg strength has been shown to be an important contributor to the development of

a kick, as well as to resultant ball velocity in a soccer kick. Narici et al. (1988) studied
the relationship between isokinetic strength of the knee extensor and hip flexor muscles
and ball velocity during a forceful soccer kick. Adult soccer players and non-soccer
players were used in the study. Narici et a1. (1988) examined the isokinetic torques of the
knee and hip at the nearest possible angular speed to that of kicking. Narici et a1. (1988)
used a starting knee angle of 150 degrees rather than the standard 90 degrees. Also, 210
degrees versus the standard 180 degrees was used for the starting hip angle. Hip flexion
was tested at 180 degrees/sec, and knee extension was tested at 300 degrees/sec. The
modification of the starting angles was used in order to maximize the subject's segment
velocities. No statistical differences were discovered between dominant and non-
dominant limbs. However, high correlations were found between maximal ball velocity
and isokinetic strength of the hip flexor and knee extensor muscles in the soccer players.
Narici et a1. (1988) concluded that the hip flexors play a more important role than the
knee extensors, therefore strength training should emphasize the hip flexors of soccer
players.

Not only has isokinetic leg strength been shown to be related to resultant ball
velocity, other variables involving power have been shown to be related to kicking
performance. Cabri et al. (1988) measured isokinetic strength of knee flexion, hip
flexion, and hip extension. Subjects were also evaluated on explosive power by the
vertical jump, standing jump and triple jump. The performance parameter of Cabri et a1.
(1988) was the ability to kick a ball a maximrun distance. The study compared soccer
players and non-soccer players. No description of the non-soccer players was given.
Soccer players were determined to be stronger than the non-soccer players across the
isokinetic variables and were able to kick the ball farther than the non-soccer players.
Kick performance was highly correlated with eccentric knee flexion, eccentric hip

extension, and the jump and reach test. Cabri et al. (1988) concluded soccer players

33
demonstrated greater kick performance because of technical skills and more efficient use

of their muscular system. The authors also stated that the correlations with kick
performance, and eccentric strength of the hamstring group resulted in an improved level
of performance as exhibited in an increase of the distance a ball is kicked. The eccentric
activation of the antagonistic group supports the "soccer paradox" discussed by DeProfi
et al. (1988). Cabri et al. (1988) recommended eccentric strength training of the
hamstring group during soccer training in addition to general strength training. Of
interest to the current author would be an analysis between soccer players and non-soccer
players of equal strength. A study between soccer players and non-soccer players may
yield different results and bring to the forefront technique as discussed by McLean and
Tumilty (1993). As a result of a study by Cabri et al. (1988), it was hypothesized that
strength training could be effective in increasing kicking performance.

The effects of strength training have been accepted as a valuable means of
improving performance in most sports. DeProft et al. (1988) studied a season long
strength training program on kick performance. The subjects were adult soccer players
(20 +/- 1.1 years old) and junior soccer players (15.5 +/-O.7 years old). Subjects were
divided into a strength training group and a control group. The strength training group
received a strength training regime of multiple repetitions at 80 percent maximum effort
of different leg muscles (specific exercises were not reported), in addition to regular
soccer training (soccer practice). The subjects involved in strength training showed
greater strength increases, as well as increases in kick performance. The non-strength
training group showed no increase in kick performance. Strength and kick performance
correlated only in the strength training group. The strength training group increased 77

percent in eccentric knee flexor strength and 25 percent in concentric knee flexor

strength. The hip flexors increased in strength by 15 percent and 35 percent, respectively.

DeProf’t et al. (198 8) suggested regular soccer training will improve strength, but adding

strength training to routine soccer training would result in increased performance. A

 

 

_ 34
point mentioned briefly by DeProfi et al. was technique. An in-depth discussion of how

technique may relate to performance was not included in the study.

Technique appears to be an important variable in kicking performance. McLean
and Tumilty (1993) studied right and lefi leg asymmetry during a drive and chip kick.
The drive kick was characterized as a low trajectory, high velocity kick to a target area.
The chip kick was characterized as a lofted kick to a target area. McLean and Tumilty
(1993) included accuracy in investigating kick performance by requiring that the subjects
kick balls to specific target areas. They also compared isokinetic knee strength with kick
performance. The subjects exhibited better performance with the right limb during a
drive kick, while no differences were present between limbs during a chip kick. The
subjects also had greater strength on the right side.

Studies have reported that isokinetic leg strength is related to kick performance,
but other variables, such as technique, may be of greater importance if related to final ball
velocity (McLean & Tumilty, 1993). McLean and Tumilty study determined that the
drive kick on the right limb (dominant) had a higher velocity (79 km/h) than the chip (66
km/h), but there were no significant differences between the drive (66 km/h) and chip (64
km/h) kicks for the left limb (non-dominant). Correlations resulted in no significant
relationship between isokinetic knee strength and kick velocity for either the right or left

limb. The left limb velocities were similar for both the drive and chip.

M

Biomechanical relationships exist within specific sequences and patterns of a
kick. Very few studies have investigated the type of ball used in soccer. As of this
writing, no studies published have included the effect of ball size or its weight on soccer
kick performance. One study in this review of literature used a smaller ball for its

younger subjects (T00 and Hoshizaki, 1984), however the researchers did not determine

 

35
if their results were attributable to the smaller ball. The balls used by the 9-12 year old

subjects in Too and Hoshizaki’s (1984) study were 347 and 349 grams (12.15 and 12.22
ounces). The study of junior soccer players (9 to 18 years old) by Luhtanen (1988) did
not use a smaller ball. The ball used in that study was a size 5 (450 grams, 15.75
ounces).

The Federation of Internationale de Football Association (F IF A) Laws of the
Game (1996) dictate that an official ball (size 5) shall not be more than 28 inches (71 cm)
and not less than 27 inches (68 cm) in circumference. The weight shall not be more than
16 ounces (453 grams) or less than 14 ounces (396 grams). In the PIP A Laws of the
Game, it is permissible, with agreement of the national association involved, to modify
the size, weight and material of the ball for players under age 16, for women, and for
veterans (over 35). Most sanctioned youth programs in the United States do use smaller
and lighter balls for youth. Sanctioned leagues for players under 16 use either a size three
or size four ball. Specific size and weights of balls are variable depending upon
manufacturer. As millions of youths play soccer world wide, the implications of the
development of appropriate size and weight balls for children are apparent.

Youth and less experienced players may be at a higher risk of injury during a
soccer match because of the types of balls used. Levendusky, Armstrong, Eck and
Jeziorowshi (1988) dropped standard soccer balls on a force plate from 18.09 meters,
which resulted in a ball velocity of 17 to 18 m/sec. Peak force and impulse data were
collected from this force plate. The mean mass of the stitched balls were 437.7 grams
(size 5; F IFA rules specify 396 to 453 grams). These balls produced a mean peak force
of 912 N and a mean impulse of 13.72 NS. Peak forces of 670 to 1100 N have been
determined to cause head or face injury. As stated in Levendusky et al. (1988), the peak
force and impulse were of a magnitude (912 N) to produce injury to the face and head.
Junior players (9-11 years old) have been shown to produce mean ball velocities of 14.9

+/- 1.7 m/sec with a 450 gram ball (Luhtanen, 1988). Levedusky et al. (1988) described

 

36
peak force as a function of ball mass and velocity. Suggestions were made to increase

technical training and limit heading for at risk populations. No recommendations were
made to reduce the size and weight of the ball, which is within the Laws of the Game
(FIFA, 1996). The reduction in ball size and weight, potentially would allow for
technical training to occur as well as increased safety.

An additional concern is water retention of the ball, resulting in an increase of the
ball’s mass. Impact intensity increases as a soccer ball retains water. Armstrong,
Levendusky, Eck, Spyropulus and Kugler (1988) investigated the effects of ball wetness
and inflation on impact intensity. The soccer balls used in the study were size five. Two
recommendations were made. First, manufacturers should develop better water repellent
characteristics for ball coverings. Secondly, it was suggested that children and
inexperienced adults not participate in soccer under conditions that promote water
retention in the ball.

Although the impact studies reviewed were specific to head injuries, inferences
can be made to the use of a light weight ball during a kick. If children used a light weight
ball, less force would be required to propel the ball. Potentially, requiring less force to
kick a ball might result in a change of the specific kicking pattern and result in an
increase in performance as measured by ball velocity. The increase in performance may
be qualitatively assessed using the MSU Developmental Sequence of Kicking

(Haubenstricker et al., 1981) and quantitatively by assessing ball velocity.

Summgry of related literature

The biomechanical literature pertaining to the world's most popular game is
prevalent. The literature covers many aspects of the game, including strength, muscle
type, muscle activation, experience, angle of approach, ball type, sequencing and timing.

However, limited literature is available examining youth soccer and kicking. To date no

 

37
published studies were found that pertain to the specific kinematic variables associated

with the development of kicking while using a direct or angled approach to the ball. The
proposed study adds to the body of knowledge in the sport of soccer and will assist in the
development of age appropriate teaching methods. The continued development of
specific strategies and pedagogy may improve methods for training, teaching, coaching

and injury prevention of youth soccer participants.

 

Chapter 3
METHODS AND PROCEDURES

The purpose of this study was to identify the differences in the selected kinematic
variables of angular displacements, velocities, and accelerations associated with children
exhibiting kicking stages one through four. Two different-sized balls, a standard size
three soccer ball and a newly developed Micro-Soccer ball, were used. In addition, two
approaches were analyzed: a direct approach and an angled approach to the ball. The best
trial for each condition was used for each subject. The selected kinematic variables '
mentioned above were analyzed and evaluations performed. A comparison of the timing
of thigh and shank movements for stages three and four performers was made for both
approaches and both soccer balls. Approval of subject selection and testing procedures
was obtained from the University Committee on Research Involving Human Subjects at
Michigan State University prior to the beginning of the study.

The procedures for the collection and analysis of the data obtained in this study
are described in this chapter. Biomechanical sampling methods used in this study were
consistent with current biomechanical research. Two preliminary investigations were

completed in order to establish the specific procedures used in this study.

38

 

39
Sample

Each potential subject and his or her legal guardian(s) were informed of the nature
of the study by the primary investigator or a trained assistant investigator and were asked
to sign an informed consent (Appendix A) prior to participation in the study.

Subjects selected for participation in this study were identified as "model" or
"classic" examples of one of the four developmental stages of kicking (Haubenstricker et
al., 1981). All subjects exhibited the classic characteristics of one of the four stages of
kicking during a pre-test kicking period. Only children who were right foot dominant
were recruited in order to standardize the biomechanical data collection procedures and
establish a homogeneous subject pool. The identification and assignment of each
subject's stage level were completed by three researchers prior to testing. These
researchers were trained in the Michigan State University developmental sequences of
selected skills, including kicking. For the current study, the researchers evaluated each
subject independently and agreed upon the classification of study participants. The
agreement reached by the three researchers increased the validity and reliability of subject
classification.

A total of 20 children, recruited from the Grand Rapids, Michigan area and
ranging in age from two to eight years, participated in the current study. This age range
was selected because of developmental considerations and subject availability, especially
in recruiting children exhibiting patterns associated with stages one and two. According
to the study by Seefeldt and Haubenstricker (1971), 60 percent of boys (girls) have
reached stage one by age two (age two), stage two by age three (age three and a half),
stage three by age four and a half (age six), and stage four by age seven (age seven and a
half).

Subjects were assigned to developmental groups based on the classic stages as

follows: two each were at stages one and two, and eight subjects each at stages three and

 

_ 40
four (see Table 3). According to Cohen's rule to estimate sample size (Rothstein, 1985),

it was determined that a minimum of seven subjects per group was required for
meaningful statistical analysis. The use of eight subjects in the two higher skilled groups

increased the power of the statistical tests.

Table 3

Sample Population

 

Stage 13
1 2
2 2
3 8
4 8

 

Two soccer ball sizes were used in this study: a standard youth size three ball and
a newly developed Micro-Soccer ball. Nationally sanctioned leagues generally use a size
three ball for the five-to-eight-year old age group. Additionally, the Micro-Soccer
curriculum was designed for five to eight year old participants and resulted in the
development of the Micro-Soccer ball. Because of the different weights and sizes
(circumferences) of the two balls (Size 3: 337.69 gm, 60.0 cm., and Micro-Soccer ball:
260.93 gm, 64.5 cm), a comparison was made of resultant ball velocities for each ball and

for each approach used by the subjects exhibiting stages three and four of kicking.

Subject preparation

Subjects wore a T-shirt, shorts and either flat soled tennis shoes or indoor soccer
shoes. Black knit shorts, specifically designed for this study were worn by each subject.
The shorts were designed to maximize subject coverage as well as allow for marking the

superior iliac spine and greater trochanter with targets directly on the skin. The right side

41
of the shorts were fashioned with a Y-shaped cut to allow for the specific anatomical

landmarks to be targeted and then closed around each target (Figure 1). During
preliminary testing, using these specifically designed shorts allowed the researcher to
identify, mark, and digitize all landmarks without difficulty. Moreover, the shorts

provided an excellent contrast to the pelvic and hip markers for the purpose of digitizing.

 

Figure 1. Test shorts.

42
Each subject had selected landmarks on the right side of the body located,

marked, and targeted by the primary investigator. The marker used was a water soluble
ink pen. The primary investigator targeted the following landmarks: the fifth metatarsal
(shoe location), lateral malleolus, point between the lateral condyle of the tibia and the
lateral epicondyle of the femur, greater trochanter, and the superior iliac spine (Figure 2).
The targets were spherical forms covered with highly reflective tape. These targets were
applied to the subject's skin with double sided hypo-allergenic tape. The targets provided
landmarks for digitization for the subsequent determination of angular displacements,

velocities and accelerations.

5 - superior iliac crest

4 - greater trochanter

3 - mid point of knee

2 - lateral malleolus
1 - 5th metatarsal

Figge 2. Target locations and order of digitization.

Anthro metric measurements

The subjects had their weight, height, total leg length, femur length, shank length,
foot height (with shoes), and foot length measured by the primary investigator following

standard anthropometric procedures (Seefeldt, Haubenstricker, Brown, and Branta, 1983).

43
These measurements were taken after each subj ect's leg was marked and prior to the

subject being targeted.

Inherent problems and accuracy of A.P.A.S.

Several shortcomings are inherent to any videographic system. The limitation
with perhaps the greatest potential for affecting any movement study is the speed of the
recording device. Normal speed of videographic recordings are too slow for recording
ballistic activities often found in sport. The A.P.A.S. runs at a rate of 60 Hz, or .017
sec/frame. Even if shutter speed were set at 1/1000 sec., as was done in the current study,
shutter speed affects only the clarity with which one can view the activity, not the
physical speed of the videotape. Critical points in a skill could be missed while the
shutter is closed.

Zoom lens use is also helpful to reduce the distance the cameras have to be placed
away from the object, while maintaining relatively large object to flame size ratio.
Determining appropriate object space size is critical to any study as it allows the joint
markers to be seen more easily for digitization purposes if the largest object to frame size
is used. Approximate object size is determined by the activity being filmed and the size
of the calibration structure used. As a result of preliminary testing, it was determined that
a 180 cm (length), 120 cm (width), and 90 cm (height) area be calibrated. It was
determined that this area was sufficient to capture the full kicking sequence of the
children used in this study.

Camera placement and number of cameras used are important parameters to any
biomechanical study. Direct linear transformation (D.L.T.) accuracy is dependent on the
accuracy of calibration. The calibration structure is used to define a volume in space in
order to know locations of points within that volume. Evenly distributed control points

covering at least total object space assists in D.L.T. Since D.L.T. residuals are not given

44
by the A.P.A.S. system as in other systems, the calibration must be exact. Specific details

on camera placement and calibration procedures are mentioned in subsequent sections.
The accuracy of the A.P.A.S. system has been calculated by several researchers.
Ball (U libarri personal communication, 1996) found less than one percent error in angular
displacement measures with this system. Klein and DeHaven (1995) reported that point
estimates were within acceptable range at less than 3.5mm. They stressed that this level
of accuracy was consistent with other comparable systems. In this same article, they
reported that angular measures were within acceptable limits of less than .3 degrees.
Klein and DeHaven (1995) and Vander Linden, Carlson and Hubbard (1992) reported
that the greatest estimated angular error was observed as the angle reached 180° in most
systems, due to the manner in which angles are calculated by the systems. In order to
deal with this internal software problem using the A.P.A.S. system, if the angle
approaches 180°, the relationship of segment angles should be used, rather than the joint
angle calculations found in the modules. Similar findings were discussed in an
unpublished study by Ulrbg and Angeli (1996). Furthermore, they cautioned that an
additional minimal error of 1.22% was added by data smoothing. The smoothing
technique desired must be given careful consideration in order to minimize the amount of
error possible. Cubic spline smoothing was the technique which added the least amount
of error to the determined measurements in their study. A priori knowledge of data trends
and how each smoothing technique addresses the data are paramount in reducing error
due to smoothing. Therefore, the cubic spline method of smoothing was utilized in the
current study. With this information in mind, the data collection setup and procedures are

explained in the following section.

45
Data collection procedures

Testing took place in a lab/classroom at Cornerstone College, Grand Rapids,
Michigan. The testing sessions were closed except to the subjects, parents of subjects,
assistant investigators, and the primary investigator. Closing the sessions prevented
curious bystanders from observing and decreased potential stage fright of the subjects.
The lab/classroom was decorated with cartoon characters to provide a festive atmosphere
for the children. Additionally, the small size of the classroom was selected to reduce
stage flight that may have occurred in a larger gymnasium setting. Based on results from
a pilot study, the subjects were scheduled in 45-minute time blocks throughout the two

days of data collection.

Reference frame

Prior to the subjects’ arrival, a calibration structure (Figure 3) which surrounded
the area in which the kick was to be performed was set up and incorporated evenly
distributed control points to improve accuracy in D.L.T. calculations. The purpose of this
calibration structure is to define the location of points in space in order that a volume of
space be defined. The calibration structure consisted of 16 control points. Four sets of
retro-reflective tape covered balls were strung by surveyor’s cord and tension was placed
on the cords by surveyor’s plumb bobs. The structure defined a calibration space of 120
cm wide by 180 cm long by 90 cm high. The control points were symmetrically
distributed and placed 90 cm, 60 cm, 30 cm and 16 cm fi'om the floor. These control
points were digitized in the order indicated on the calibration structure in Figure 3. The
calibration structure was filmed and then removed from the filming area. Tape marks
which had been placed under the pltunb bobs were left on the floor to mark the floor

space of the calibration volume.

46

180 cm

 

3 \I20 cm

12 A

 

N

11

’

90
cm

a,

 

1O

 

 

 

 

 

 

Figge 3. Calibration structure.

Two S-VHS cameras (Panasonic S-VHS Reporter, AG-455) were used to record
the trials. The cameras were set to film each trial at 60 frames per second (fiame time =
.017 sec) and had a shutter speed of 1/ 1000 second as determined during preliminary
testing. Both cameras were equipped with zoom lenses. Each camera was mounted on a
tripod and was operated by a trained assistant during the actual filming of subjects. Prior
to subject filming, the zoom lenses were focused in on the calibration structure so that all
control points were visible with the largest possible image in the flame. This allowed the
largest object to frame size ratio which helped decrease error in digitization because the
markers were as large as possible relative to the calibration space. The cameras were
placed at an angle of approximately 60 degrees to each other, in the sagittal plane, to the
right side of each subject's kick. Camera one was to the right and slightly to the rear of
the soccer ball placement and camera two was located to the right and slightly forward of
the soccer ball placement. The camera placement allowed for all targets to be in the field
of view for each camera. Timing lights were placed in the field of view of both cameras
for synchronization of frames during data reduction. An eight millimeter Sony video-

carnera was positioned directly to the right of the ball placement in the sagittal plane and

47
was used by the investigator to validate the subject's pre-assigned stage level. Filming

began on an oral signal from the primary investigator before the subject began the
approach run and ended on an oral signal after the subject completed the kick. The trials

for all 20 subjects were recorded in this manner. The test area is illustrated in Figure 4.

O / Timing lights \
_ ID board - =

 

    
 
 
    

oooooooooooooooooooooooooooooooooooooooooooooooooo

Vitalitrasflfiaj

Intetfaded direction of ball —>

 

   

Ball :----:':.-. ..
placement - €31“ ck
. area "

 

 

 

 

Camera 1 8mm camera Camera 2

 

< >

6 meters

Figure 4. Test area setup.

Identification of subjects and trials

To identify the subjects and trials, a dry erase board was placed in view of each of
the two cameras. The board contained a three digit number plus two letters. The first
two digits represented the subject number (01 - 20), the second series of identifiers
represented the trial number, the first letter represented the ball (A - Micro Soccer ball
and B - standard size 3 ball), and the second letter represented the approach type (D -
direct and A - angled).

48
Kicking procedures

Following a warm up period of five minutes of kicking with a rubber playground
ball, all subjects completed three good trials with each ball type utilizing a direct
approach to the ball. The five minute warm up was deemed appropriate because the
kicking trials were within routine play for children, therefore risk of injury was minimal.
The Stage Three and Four subjects also performed three good trials of the kick using an
angled approach for each type of ball used in this study. A total of six good trials were
recorded for the stage one and stage two subjects, whereas a total of 12 good trials were
recorded for each subject in stages three and four. Three good trials per ball were
selected in order to ensure that foot/ball contact was captured during fihning. From those
three good trials, one best trial was chosen for analysis based on foot ball contact.

The direct approach as used in the MSU developmental sequence of kicking, was
one technique analyzed for this study. A 45 degree angled approach also was used by
each subject classified as Stage Three or Four. To aid each subject's approach, two lines,
one for each approach were taped on the floor using electrical tape. One taped line was
parallel to the intended line of flight, while the second taped line was 45 degrees to the
intended line of flight of the ball. The subjects were allowed a maximum of a four meter
approach to the ball, and could start anywhere on the respective approach line.
Limitation of the approach distance eliminated an excessive run to kick the ball. Each
subject was randomly handed either the Micro-Soccer ball or standard ball as determined
by a table of random numbers, with an even number being assigned to the Micro-Soccer
ball and an odd number being assigned to the standard ball. While the subject was
holding the test ball, the primary investigator demonstrated the specific type of kick for
each subject. The subject was instructed to place the ball on a taped mark on the floor
and back up as far as desired, but not past the end marker (orange cone). The subject was

then instructed to kick the ball as hard as possible toward a stationary wall. Each subject

49
was given as many extra trials as necessary to obtain three good trials. The "miss

kick/out of bounds" area was taped on the floor to aid the researcher in the determination
of a miss kick (Figure 4).

Following the trials, the subject and parents were taken by an assistant
investigator to an adjoining room and asked a series of exit questions (Appendix C).
These questions were used to assess the subject's perceptions of the two balls. As a result
of each subject handling the two balls (treatment levels) and personally placing them on
the floor to be kicked, the assumption was that the opportunity for gaining personal
perceptions of the ball were standardized across the subjects. It should be noted that both
balls were of similar color (yellow) and design pattern. The balls were of a similar color

in order to eliminate any confounding influence color may have had in this study.

Data reduction

The Ariel Performance Analysis System (A.P.A.S.) was used to digitize
the video data and to calculate angular displacements, velocities and accelerations. The
calibration structure was digitized first in accordance with this system’s procedures.
Prior to digitization, the best trial for each approach and ball for each subject was selected
by the primary investigator after viewing the three best recorded trials and selecting the
trial with the best view of foot/ball contact. Within the grabbing module of A.P.A.S,
every frame from five frames before support foot contact to five fiames past the
maximum follow through position was selected for analysis. The order of digitization
remained the same for each subject (Figure 2), beginning at the fifth metatarsal and
ending with the superior iliac crest. The A.P.A.S. transformation module was used to
combine the two, two-dimensional digitized views of the two cameras. The result of this
transformation of data was the three-dimensional points used in the analysis. Data were
smoothed using the cubic spline method within the A.P.A.S. system. Angular

displacements, velocities, and accelerations were calculated and analyzed for the

50
segments defined by the points digitized. Hip joint angles were calculated between the

pelvis and the thigh segments defined by the superior iliac crest and greater trochanter,
and the greater trochanter and mid point of the knee markers, respectively. Flexion was
defined as a decrease in angle, whereas extension was defined as an increase in angle.
Knee joint angles were calculated between the thigh and the shank segments defined by
the greater trochanter and mid point of the knee, and the mid point of the knee and lateral
malleolus markers, respectively. A hip joint angle of approximately 90° , and a knee
joint angle of 1800 indicates that the hip is in a flexed position, while the knee is straight,
or fully extended. The specific joint angles were calculated between the adjacent
segments as follows: Segment angles are measured from the horizontal of the last point
digitized for that segment, counter clockwise, to the segment itself, as depicted in Figure
5(a). Then a second segment angular measure is calculated fiom that same horizontal line
to the more proximal segment. Therefore, the hip angle was calculated by subtracting the

thigh segment angle from 360°, and then adding pelvic tilt angle.

    

pelvic tilt angle
. " Superior Iliac Crest
thigh segment ‘
angle \‘
--- Greater Trochanter 166°
thigh segment angle
shank segment '
““9” 148°
-. Mid Point of Knee

Lateral Malleolus
5th Metatarsal

a. b.

Figure 5. Segment and joint angles. (a) Method for segment angle calculations. (b) Joint
angles used after segment angle calculations.

51
The knee joint angle was calculated by taking the shank segment angle and subtracting

from it the thigh segment angle. Figure 5(b) illustrates hip flexion of 166° and knee
flexion of 148°.

Statistical analysis

The data collected were used to test the following hypotheses:

1. Each of the kinematic variables will follow the predicted trends as stated (see p. 7).

Kinematic variables:

The kinematic variables include the angular displacements, velocities, and
accelerations of the thigh and shank segments at distinct positions during the kick. These
positions were: a) maximum backswing of the kicking leg, b) foot/ball contact and 0)
maximum forward movement of the kicking foot after the ball leaves the foot.

These kinematic variables were expected to follow the predicted trends, for each
stage for each approach, as defined for the preparatory phase, contact phase (force

production phase), and the follow through phase.

2. There will be a difference in the rotations of the thigh, as well as the shank, of the
kicking limb between subjects exhibiting stages three and four, while using a standard
youth soccer ball and a direct approach to the ball. The stage four subjects will exhibit a
more mature pattern of the kicking limb than the stage three subjects, as rotation of the
thigh will be greater in the initial portion of the force production phase, with minimal
rotation of the shank about the knee joint. In the later portion of force production phase,

thigh rotation will decrease as shank rotation increases to ball contact.

52
3. There will be a difference in the rotations of the thigh, as well as the shank, of the

kicking limb of the subjects using a direct approach, when compared with subjects using

an angled approach, while kicking a standard youth soccer ball.

4. The resultant ball velocity of the light weight soccer ball will be greater than that of
the standard youth soccer ball, regardless of approach.

Following data reduction, a computation of the descriptive statistics for the
selected kinematic variables was performed with the Mini-Tab computer program. An
ANOVA (Mini-Tab Software) was used to test each of the hypotheses with a significance
level of p < .10 used in order to maximize the sensitivity of the test. Several
biomechanical studies have questioned the use of a low significance value or have used a
more generous significance level in the statistical treatment of data (Barfield, 1995;
Kiger, 1987). The use of a p<.10 was determined to be acceptable as a result of the work
by Kiger and Barfield. Additionally, further support for the use of a p<.10 is that, in
human movement research, gross measurement methods, including videography, joint
marker placement, and digitization, may obscure subtle human movements. The use of a
p<.05 increases the risk of missing real differences as a result of the data collection and
reduction processes. Furthermore, since qualitative characteristics distinguish points
along a continuum of elementary to mature skill, and since biomechanical research
techniques are more likely to distinguish extremes rather than gradations in performance
(Ulibarri, personal communication, February 21, 1997), the use of a p < .10 is further

supported in this study in order to identify differences in performance.

Chapter 4

RESULTS AND DISCUSSION

A biomechanical analysis was used in this study to investigate quantitative
variables associated with the development of kicking in children three to eight years of
age. Videographic methods were used to record the kicking trials of 20 children.
Subsequent digitization of selected trials provided two, two-dimensional sets of data
which using D.L.T. provided three-dimensional coordinates. Selected kinematic
variables, at specific periods during a kick, were obtained for analysis from these sagittal
plane three-dimensional coordinates.

Three purposes were identified for this study and were discussed in the following
pages. The areas of investigation were: (a) to identify the selected kinematic variables of
angular displacements, velocities, and accelerations associated with children exhibiting
kicking stages one through four (Haubenstricker et al., 1981) during a direct approach,
using both a standard size three soccer ball and a newly developed light weight soccer
ball; (b) to identify the differences in the selected kinematic variables associated with
children exhibiting kicking stages three and four using direct and angled approaches to
the ball; and ( c) to identify the effect ball weight had on the selected kinematic variables
for stage levels three and four, by examining resultant ball velocity relative to the

approach used.

53

54
Kinematic variables

The selected kinematic variables included the angular displacements, velocities,
and accelerations for the thigh as well as the shank. Three specific points in a kick which
coincided with the end of the preparatory phase, the contact period of the force
production phase, and the end of the follow through phase of a kick were used as the
periods in the skill from which the selected kinematic variables were calculated: (a)
maximum back swing of the kicking leg (MBS); (b) foot and ball contact (FBC); and (c)
maximum height (MFM) of the kicking foot in the follow through .

Developmental trends for the gross motor skill of kicking using a direct approach
to the ball have been identified by several researchers (Seefeldt and Haubenstricker,
1972; Haubenstricker et al., 1981). The current study quantified predicated
characteristics of selected kinematic variables for stages one through four, using a direct
approach, when kicking a standard youth soccer ball. Additionally, this study
incorporated a newly developed lightweight ball to determine if ball weight had an effect
on the identified selected kinematic variables. Furthermore, predicted characteristics of
selected kinematic variables were developed for an angled approach by Basic Stage and
Mature Stage kicking skills. These predicted characteristics were identified for both the

standard size three ball and the Micro-Soccer ball.

Developmental trends for the direct approach

The developmental sequences of kicking by Seefeldt and Haubenstricker (1972)

provided a foundation from which to quantitatively assess the sequences of changes

55
associated with the development of kicking in children. (For a detailed review of the

sequences, see pages 20 - 22 of Chapter 1.) The results of children exhibiting stages one
through four using a direct approach to kick a standard youth soccer ball (size three) and
a lightweight soccer ball, were presented within this section. The current study examined
the effect of ball weight on selected kinematic variables of kicking in children by use of

the Micro-Soccer ball, a newly developed light weight soccer ball.

Preparatog phase

The preparatory phase of any gross motor skill is important in executing the skill
with the utmost success, as this phase establishes the foundation for the specific
technique a subject will use in developing force, by placing the body in a position for
force production. It was predicted that the stage one performers would not exhibit
hyperextension of the hip joint, while the stages two through four performers would have
increasing amounts of hip joint hyperextension. This predicted trend was developed on
the premise that, as skill level increased, the approach stride length of the stage three and
four performers would increase, resulting in hip hyperextension of the kicking leg . A
greater stride toward the ball is important as it increases the distance through which the
leg can swing, allowing the leg to reach higher velocities, prior to contact, than if a
shorter stride were used.

The joint angles of the hip for all stages did not meet the predicted angles
expected during the preparatory phase. Using the standard soccer ball the stage one

performers exhibited a neutral position at 180°. Stages two, three and four performers’

56
hip angles were 171°, 177° and 174° respectively. Therefore, subjects in stages two

through four did not exhibit increasing hip hyperextension during maximum backswing
as was predicted (Table 4). Likewise, the subjects using the lightweight Micro-Soccer
Ball did not exhibit increasing hip hyperextension (Table 4). In comparison with the
results of the standard ball the stage one subject’s hip was more flexed using the Micro-

Soccer Ball (Figure 6, Note: for ease of drawing, figures are oriented to the vertical).

Table 4

Elem-Ligand Kne_e Joint Angles (dggrees) at Maximum Backswing for Stages 1 - 4

 

Stage 1 2 3 4
Hip (MBS)
Standard Ball 180 171 177 174
Micro-Soccer Ball 162 174 175 168
Knee(MBS)
Standard Ball 160 161 135 142

Micro-Soccer Ball 157 172 128 139

 

Standard 180° 171° 177° 174°

Ball 0
1600 1610 1350 142

Micro-Soccer 162° 1740 1750 168°
Ball
157° 172° 128° 139°

Figure 6. Mean hip and knee joint angles at maximum backswing, stages 1 - 4.

57
Perhaps a misperception of the trunk position relative to the thigh, may explain

the absence of the hyperextended hip position as described by Haubenstricker et al.
(1981). As the performer becomes airborne, and if the trunk is inclined anteriorly, at
maximum backswing of the kicking leg, hip hyperextension may appear to be present.
However, if the position of the trunk is examined relative to the thigh, this
hyperextension may not exist. This misperception may result in inaccurate assessments
of hip positions relative to the trunk. Additionally, hyperextension of the lumbar
vertebrae could result in a similar misperception of hyperextension at the hip. Lumbar
hyperextension would cause an anterior rotation of the pelvis and, relative to the thigh,
may appear to be hip hyperextension.

It was expected that knee flexion at maximum backswing would increase
sequentially fiom stage one to stage four. Using the standard soccer ball, the values for
the knee joint were similar for stage one at 160°, and stage two at 161°. Extension was
found between stage one (157°) and stage two (172°) with the Micro-Soccer Ball. The
stage three performers had greater knee flexion than the stage two subjects 135° and 128°,
respectively, for the standard ball and Micro-Soccer ball. The difference between stages
two and three can be attributed to the use of a deliberate approach of the stage three
subjects. The use of a deliberate approach would enable the stage three performers to
take advantage of increased momentum, both of the body and kicking thigh, which would
result in greater knee flexion. However, an increase in extension was observed fiom stage
three to the stage four subjects, 142° and 139° for the standard and Micro-Soccer ball
respectively. The stage four subjects’ more extended knee, in comparison to the stage

three subjects, may have been due to being airborne. The stage four subjects most likely

58
capitalized on the increased momentum of the body and may not have required as much

knee flexion in comparison to stage three (Table 4).

The similarity of stages one and two (standard ball) can be explained by the
stationary approach used by the subjects, which resulted in similar backsvvings. The
difference seen in the stage three and four subjects could have been as a result of greater
coordination during the backswing for the stage four subjects. Knee flexion which was
expected to increase sequentially across the stages, was not found (Table 4), with only
stage three performers exhibiting an increase in knee flexion from stage two. Stage three
performers used a deliberate but not airborne approach to the ball. As a result of not
being airborne, the stage three subjects may have required greater knee flexion in the
preparatory phase in anticipation of generating force during the force production phase of
the skill. '

When the hip joint was examined in conjunction with the knee joint during
backswing, the stage one subjects moved the thigh and shank of the kicking leg as a
single unit when using the Micro-Soccer Ball (Figure 7). The large difference from stage
two to stage three using both ball types was likely as a result of a moving approach for
the stage three subjects. As a result of the increased momentum of the body or thigh, or a
combination of both for stage three performers, knee flexion occurred, as the hip joint
remained relatively extended during the final step. The relationships of knee and hip
angles at maximum backswing between the stages for the direct approach kicking both
ball types, illustrated in Figure 7, could be explained by the stage four subjects’ leap, on
the last step of the approach. All of the stage four subjects exhibited a leap, in contrast to

the stage three subjects who all used a step with their approach. An increase in

59
coordination and timing between the thigh and the shank for the stage four subjects

would be expected when compared to the stage three subjects.

 

 

 

 

 

 

 

 

 

 

 

I 190
I
, 180,
‘ 170 it —\
160 _4 +1-b(Standard)
§ !/ +Hl>lMcr0)
3. 150 0 +Knee(Standard)
+WIMcro)
140 I I
130 .1
120 -
1 2 3 4

 

 

Figge 7. Knee and hip angles at maximum backswing for stages 1-4.

The stage three subjects may have to rely more on the stretch reflex of the muscles
involved in the kick than the stage four subjects, and would have positioned the segments
in order for the muscles to invoke the stretch reflex. The stage four performers, it would
seem, would have both the body’s momentum and the stretch reflex, whereas the stage
three performers would have only a step and the stretch reflex. Additionally, the stage
four performers, because of the increased momentmn, do not need as great of a
contribution from the stretch reflex, although the reflex is probably invoked due to

reversal of the thigh forward relative to the shank, in the backswing. The stretch reflex

60
has been described as a self regulatory mechanism, enabling the muscles to automatically

adjust as a result of increased load or length, in order to support the desired movement
pattern, resulting in a stronger contraction than if the reflex had not been involved

(McArdle, Katch & Katch, 1996).

Contact phase

The force production phase of a kick is critical in assessing performance, as this is
where the culmination of the subject’s technique is expressed. The orchestration of the
movement pattern is exhibited in the velocity of the kicked ball. Maximum ball velocity
(Luhtenan, 1988) or angle of ball projection (T 00 and Hoshizaki, 1984) was used by
researchers to assess kicking performance. The study by Luhtenan (1988) helped in
validating the results of the current study. Luhtenan determined resultant ball velocity to
be 14.9 m/sec for the 9-12 year old subjects in his study. For the most skilled kickers in
the current study, ball velocities for the direct approach were 11.66 and 14.24 m/sec for a
standard youth soccer ball and a lightweight soccer ball, respectively. At the time of this
writing no studies had investigated angular displacements, velocities and acceleration for
children while kicking. Motor skill development is age related but not age dependent.
Therefore, the comparison of segment rotations between adults and children would be a
study of its own. This researcher predicted that the angular displacements, velocities, and
accelerations of the kicking leg segments would increase from stage one through stage
four. Additionally, it was predicted that the knee joint of the kicking leg would have a

greater amount of extension at ball contact for stage four performers than stages one

61
through three, and that the stage four performers would reach full knee extension (180°)

at ball contact.

The stage one performers positioned the thigh at a mean hip angle of 155° with the
standard ball and 150° with the Micro-Soccer Ball. This flexed position was different
than the expected position of 90° of hip flexion as was predicted and as was described by
Haubenstricker et al. (1981). Slightly different hip joint angles for all four stages were
found, with an overall mean range of 150° to 162° at contact, for the standard youth

soccer ball and 145° to 154° for the Micro-Soccer Ball (Table 5, Figure 8).

Table 5

Mean Hip and Knee Joint Angles (dggrees) at Contact for Stages 1-4

 

 

Stage 1 2 3 4
Hip(F BC)
Standard Ball 155 162 154 150
Micro-Soccer Ball 150 154 152 145
Knee(FBC)
Standard Ball 127 112 89 89
Micro-Soccer Ball 131 108 95 95
_g_Sta e .1. 2 3 5
Standard 1550 1620 1500
3,, 127% > 1540
112° 89° 89°

M' .3
3:1“) 0°C“ 1500 1540 1520 1450
0 0
1310 1080 9° 95

Figure 8. Mean hip and knee joint angles at contact, stages 1 - 4.

62
The exact position of the knee at ball contact has been described by Plagenhouf

(1971), and was predicted to be at full extension at ball contact for the stage four
performers. The performers were predicted to have sequentially increasing degrees of
knee extension from stages one to four, respectively. Instead, flexion at the knee joint
was found to increase sequentially across stages at contact for both soccer balls. Only
minimal differences in knee flexion angles were found between ball types. The range of
knee joint position for the stages with the standard ball was from 127° for the stage one
subjects, to 89° for the stage four subjects. The ranges of knee joint position were similar
with the Micro-Soccer Ball (Table 5, Figure 8). Full knee extension was not reached at
contact for any performer at any stage with either ball.

The relationship between the hip and knee angles at contact were illustrated in
Figure 9. Stage levels are located along the X axis, with degrees along the Y axis. As
stage level increased from stage two to stage three the knee angle decreased and the hip
angle decreased, while maintaining a flexed position. The increase in the hip angle from
stage one to stage two was due to the increased momentum generated by the stage two
subjects versus stage one. The decrease in hip angles from stages three to stage four

reflected the segmental relationship discussed by Putnam (1991).

63

 

 

180 1.

 

 

 

‘fii +I-iptaandard) ;
+ ”0 (Mom) |
I
j

 

+ Knee (Mcro)

 

 

 

 

 

 

 

Stage

+ Knee (Standard) .

 

 

 

Figure 9. Relationship at contact between the knee and hip joints during the direct

approach for stages 1-4.

According to Plagenhoef (1971), in order to reach maximum force production
during a kick, the knee must be fully extended to take advantage of the summation of
forces involved with the skill of kicking. As was discussed earlier, Putnam (1991) did not
fully agree with this theory as applied to kicking. Putnam’s disagreement dealt with the
lack of explanation of the relative contributions of the segments. Putnam further
discussed that if one looked only at the distal segment’s maximum speed (summation of
forces), one would sense that at the moment of impact all the joints involved during a
kick would be fully extended and the angular rotations of the segments would be equal to
each other. Investigations by several researchers (Barfield, 1993; Putnam, 1983;

Luthanen, 1988; Isokawa and Lees, 1988; Glassow and Mortimer, 1968) of angular

_ 64
rotations of the leg segments during a kick have shown these rotations not to be equal at

impact. Putnam (1993) also stated that the proximal to distal sequence observed in the
pattern of kicking could not be explained by a concomitant sequence of muscle forces.
Putnam stated that there is no evidence that the forward swinging motion of the shank in
kicking, running, or walking was initiated by the larger muscles of the proximal segment
and continued by the smaller muscles of the distal segment, as suggested in the
summation of forces principle. Putnam’s theory helped to explain the contribution of the
segment motions related to the outcome of a kick.

The results of the current study indicated that different patterns of movement were
evident in the sample of children than predicted. The finding of a sequential increase in
knee flexion fiom stages one to four was in direct opposition to the work by
Haubenstricker et al. (1981). Additionally, the National Soccer Coaches Association of
America (N SCAA) academies for coaches teach a flexed knee at contact for skilled
soccer players. A flexed knee is achieved by instructing the athlete to position the knee
over the ball at contact. Because the foot is fixed in plantar flexion at contact, knee
flexion is required in order to prevent the foot fi‘om striking the ground prior to ball
contact. Also, the figures in the text by Gallahue and Ozman (1998) show knee flexion at
contact for a mature level performer.

It was hypothesized that angular displacements, velocities and accelerations of the
segments of the kicking leg would increase with each stage level. Contrary to the tested
hypotheses, not all variables were found to increase progressively across stages using the

standard soccer ball nor the Micro-Soccer ball (Table 6).

65

Table 6

Kinematic Variables for Subiects' Stages 1-4 at Contact

 

Stage 1
Angular (standard ball)
Mean Displacement (deg)
Shank 237
Thigh 282
Mean Velocity (deg/sec)
Shank -80
Thigh 292
Mean Acceleration (deg/secz)
Shank 3606
Thigh 1417
Angular (Micro-Soccer ball)
Mean Displacement (deg)
Shank 238
Thigh 288
Mean Velocity (deg/sec)
Shank 24
Thigh 287
Mean Acceleration (deg/secz)
Shank 3642

Thigh 3

214
281

6239
864

221

293

306
468

7358
36

205
295

572
603

12012

-1639

217

301

690
428

7596
-3958

213
301

1012
538

8355

-6698

221

306

1146
522

7900
-8044

 

66
Shank angular displacements decreased from stage one (at 237°) sequentially to

stage three (205°) and then increased from stage three to stage four (213°) with the
standard ball. A similar decrease in the shank angular displacement was also found for
the Micro-Soccer ball (Table 6). The change seen from stage one to stage three could
have been as a result of the deliberate, moving approach of the stage three subjects. The
moving approach would have resulted in greater knee flexion for the stage three subjects,
compared to subjects in stages one and two, as a result of the increased momentum
generated by the shank segment of the stage three subjects. The increase in shank angular
displacement was likely due to the initial forward movement of the shank (extension of
the knee). Although mean thigh angular displacement decreased slightly from stage one
(282°) to stage two (281°), upon closer examination showed that the displacement
between these two stages was maintained with use of the standard ball. An increase in
mean thigh angular displacement was seen between stage two (281°) to stage three (295°)
and again increased slightly between stages three and stage four (301°). A slight increase
in thigh angular displacement across the four stages was illustrated with Micro-Soccer
ball use. The progressive increase in angular thigh segment displacement indicated that,
across the stages, hip flexion occurred during kicks, for both soccer balls. Hip flexion
would be expected to increase across the stages due to a more coordinated timing of the
kicking sequence, as the stages progressed from stage one to stage four.

Mean shank angular velocity increased across the four stages from -80 deg/sec
(stage one) to 30 deg/sec (stage two), increased dramatically to 572 deg/sec for stage
three and increased again to 1012 deg/sec for stage four with the standard ball. Kicking

the Micro-Soccer ball (380 deg/sec) did not result in as great of a difference in mean

67
shank angular velocity between stages two and three as with the standard ball (500

deg/sec). An approximate 500 deg/sec increase occurred in mean shank angular velocity
between stages three and four, using both balls. As discussed earlier, the stage one
subjects moved the leg segments as one unit which limited velocity, whereas the stage
two subjects moved the thigh and shank independently. The stage two performers would
be able to achieve increased velocity over stage one performers as a result of the
independent movement of the shank relative to the thigh. The increase fiom stage two to
three can be attributed to the moving approach by the stage three subjects causing greater
velocities to be achieved. The increase between the stage three and four subjects can be
explained by the airborne phase on the last step by the stage four subjects. This leap
increased the velocity of the body, and since momentum is the product of mass and its
velocity, the stage four subjects were able to capitalize on the forward movement of the
body, resulting in increased segment velocities over stage three performers.

Mean thigh angular velocity with the standard ball increased from stage one
(292deg/sec) to stage two (446 deg/sec) and increased again between stage two and stage
three (603 deg/sec). A decrease in mean thigh angular velocity of 65 deg/sec was found
between stage three (603 deg/sec) and stage four (538 deg/sec) with the standard ball.
Similarly with the Micro-Soccer ball, mean thigh angular velocity increased from stage
one to stage two (Table 6). However, it decreased from stage two to stage three. An
increase in mean thigh angular velocity was found between stages three and four with the
Micro-Soccer ball. The difference in thigh angular velocity between stages three and four

could be attributed to the soccer paradox found in the stage four subjects.

68
The mean shank angular accelerations with the standard ball increased by 2633

deg/sec2 from stage one (3606 deg/secz) to stage two (6239 deg/sec’) and increased by
5773 deg/sec2 between stage two (6239 deg/secz) and stage three (12012 deg/secz). The
mean shank angular acceleration with the standard ball decreased 3657 deg/sec2 between
stage three (12012 deg/secz) to stage four (8355 deg/sec’). The rate of change in angular
velocity of the shank for the stage four subjects was not as great as for the stage three
subjects which resulted in a deceleration of the shank for the stage four performers while
using the standard ball. This deceleration illustrated differences in timing and
coordination between the stages. Using the Micro-Soccer ball a progressive increase in
angular acceleration of the shank was found from stage one (3642 deg/secz) to stage four
(7900 deg/secz). The progressive increase from stage one to stage two illustrated the
increased capability of the stage two subjects to produce increased segmental rotations as
a result of moving the thigh and shank independently to contact.

The mean thigh angular acceleration with the standard ball progressively
decelerated fi'om stage one (1417 deg/secz) to stage two (864 deg/secz), from stage two to
stage three (-l639 deg/secz), and from stage three to stage four (-6698 deg/secz). In
contrast, using the Micro-Soccer ball, mean thigh angular acceleration minimally
increased from stage one to stage two (33 deg/secz, Table 6). A progressive deceleration
occurred from stage two to stage three as in the results with the standard ball results. The
progressive sequential deceleration of the thigh was explained as a result of the increasing
skill level from stage one to stage four. As found in the literature, as skill level increased,
the thigh decelerates to the point of possibly reversing direction at contact. The

decreased shank accelerations of the stage four performers could be attributed to a more

69
coordinated movement pattern, which includes the soccer paradox. The stage four

subjects likely relied on and were able to capitalize on the contributions of the
deceleration of the thigh.

The prediction for both ball types that the stage four performers would exhibit a
decrease in thigh angular velocity, as the shank angular velocity increased to ball contact,
was supported by these data. The stage four performers’ mean angular velocity of the
shank was greater than that of the thigh angular velocity (Table 6). Not surprisingly, this
segmental relationship was further supported by the accelerations of the thigh and shank.
The shank continued to accelerate at ball contact, but the thigh decelerated for the stage
four subjects (Table 6). In comparison, the stage three subjects’ mean shank and thigh
angular velocity was lower than the stage four subjects at contact with the Micro-Soccer
ball. Although not predicted, the stage three subjects’ shank continued to accelerate at
contact, while the thigh decelerated. One might conclude from this comparison that the
soccer paradox existed for the stage three subjects with both ball types. However, the
differences in magnitude between the rotations of the shank and the thigh of the stage
four subjects were much greater and characterized the more mature pattern of this fourth
stage. Additionally, the deceleration of the thigh was much greater for the stage four
subjects, which was consistent with the literature on skilled performers. These segmental
relationships were found in the stage three and four performers’ results for both ball types

used: the standard soccer ball and the Micro-Soccer ball.

70
Follow through phase

Knee extension was predicted to continue after ball contact during the follow
through phase of the kick and was supported by the data analyzed. Although the absolute
knee angles were not seen to increase sequentially across stages, the relative change in the
knee joint angles, in fact, did increase with stage for both ball types, with the exception of
the stage three performers using the Micro-Soccer Ball (see Table 7, A Deg). The
standard ball knee angles are listed first followed in parentheses by the angles for the
Micro-Soccer ball in Table 7. The column, A Degree, was found by taking the knee joint
angles at contact and subtracting them fi'om their respective stage knee joint angles at
maximum forward movement. Figure 10 is provided to aid the reader’s understanding of
the positions of the segment’s relationships to each other (Figures are oriented to

vertical).

ID.)

A

.1. 2.
126°
Standard { % 141° \
Ball 0 o 0
189° 180 175 180

Micro-Soccer 126° 136°
Ball \ 132° K

o o o

171 186° 179 175

F 'gure 10. Mean hip and knee joint angles at maximum forward movement,
stages 1 - 4.

71
The knee joint angle extended from contact to maximum forward movement of

the kicking foot across all stages with both ball types. Slight hyperextension of the knee
was seen in the stage one and two performers at maximum forward movement with the
standard ball. Only stage two exhibited slight knee hyperextension with the Micro-Soccer

Ball.

Table 7

Knee Joint Angles (dggrees) from Contact to Maximum Fontvard
Movement for Stages 1-4 with a Standard Ball (Micro-Soccer Ball)

Stage FBC MFM A Deg
1 127(131) 189 (171) 62 (39)
2 112 (108) 181(186) 69 (78)
3 89 (95) 175 (179) 85 (84)
4 89 (95) 180 (175) 91 (79)

 

Although no hypotheses were formulated pertaining to the relative change in knee
joint angle from contact to maximum forward movement, the change in knee joint angle
may be a more appropriate method for illustrating differences between stages than solely
examining a single point during the follow through. Examining the relative changes
provides information related to the changes taking place during the sequence. Although
the analysis in this study considered only the leg segments, it is likely that other body
segments may play a role during the follow through. For example, the opposition of the
arms relative to the legs would be expected to aid in the timing of the kick and balance of
the body. Also the decrease in relative knee joint angles of the kicking leg may be related

to balance, specifically while in the air. Given that the stage four subjects were airborne,

7 2
the decrease in the relative difference of the knee joint angle from stage three may have

been a result of an in flight spatial adjustment. The decrease in the moment arm of the
leg about the hip would aid in the performer’s balance.

The final predicted characteristic during the follow through phase was that the
stage four subjects would be airborne following contact. All of the stage four performers
were airborne in the follow through phase, firrther supporting the identification of those
subjects as stage four. Only two of the stage three performers appeared to be aggressive
enough in the kick to exhibit plantar flexion on the support foot during the follow through
phase, but the momentum produced by the kick was not great enough to cause the
subjects to become airborne. Because of other criteria for stage four classification, had
the stage three performers become airborne, they would have not been classified as a
stage four performer.

Few of the predicted characteristics were found for the direct approach with a
standard youth soccer ball and the lightweight Micro-Soccer Ball. The predicted
characteristics that were found occurred at contact. At contact, angular acceleration of
the thigh decreased and knee flexion increased sequentially across all stages. The mean
shank angular velocity was found to increase across the stages, accompanied by a
progressive increase in the angular acceleration of the shank. Additionally, because a
simultaneous decrease in thigh'velocity was accompanied by an increase in shank
velocity for the stage three performers these subjects may have exhibited the beginnings
of the segmental relationship of the soccer paradox. Finally at contact, the stage four
subjects exhibited the segmental relationship of a decrease in thigh velocity as the shank

increased in velocity. The stage four subjects exhibited a greater difference between the

7 3
rotation of the thigh and shank when compared to the stage three subjects, indicating a

higher skill level for stage four. During the follow through, all of the stage four subjects
were found to be airborne. Based on these results it appeared that a lightweight ball
(Micro-Soccer Ball) did not have an effect on the specific patterns of movement of the

children selected for the current study.

Developmental trends for the angled approach

Developmental sequences for the gross motor skill of kicking have been published
in the literature and were discussed earlier. To date no literature has been found on the
developmental sequences of an angled approach to a ball, as is seen in soccer players.
Subjects who matched criteria for stages three and four (Haubenstricker et al., 1981) were
firrther examined using an angled approach. As previously stated, the reason for the use
of only stages three and four, was that stages one and two do not use a deliberate
approach to the ball; rather they stand directly behind the ball and strike the ball without
an approach. For the angled approach, the stage three performers were identified as Basic
Stage performers, while the stage four performers were considered Mature Stage
performers. Distinguishing characteristics of the Basic and Mature Stages were
established in this study, and the results of the collected data were presented in this
section. A detailed description of the predicted angled approach characteristics were

outlined in Chapter One, pages 10 and 11.

7 4
Preparatog phase

During the preparatory phase of the angled approach, the performer followed a
line off-set 45° relative to the direct approach of the ball. On the final step, it was
determined that the support foot of the non-kicking leg was positioned along the angled
approach path for all Basic Stage subjects for either ball. This foot positioning, resulted
in several instances where the ball struck the matted wall well to the right of the center of
the mat.

In contrast, all mature Stage performers placed the non-kicking support foot along
the intended path the ball was to be kicked, rather than along the approach path, for both
soccer ball types. A skill level pattern higher than a Basic Stage level appeared to be
required to execute correctly an angled approach to the ball in order to direct the ball in
the intended direction. Although accuracy was not a variable in this study, the above
comment was an observation about the foot placement of the non-kicking support leg
relative to the resulting direction of ball travel. The positioning of the support foot for
both stages reinforced the postulated view that a higher skilled kicker will place the
support foot along the intended line of flight of the ball. This foot positioning enables
the higher skill level participant to involve more muscles over a greater range as a result
of the body’s position about the foot placement. Since the support foot leg is outwardly
rotated, the muscles that are involve in inward rotation and adduction are utilized,
increasing the amount of force applied to the kicking system. Additionally, the pelvis
moves through a greater range of motion, which in tm'n carries the foot of the kicking leg

through a greater range of motion and, in theory, aids in force production. Not only are

75

more muscles involved, but the skilled performer is also more capable of directing the

ball in the intended direction as a result of the support foot placement.

During the preparatory phase, hip hyperextension for the Basic Stage performers

was predicted to occur, but in fact was not supported by the findings. The Basic Stage

performers exhibited slightly more hip flexion with the standard ball than with the Micro-

Soccer ball (Table 8, Figure 11). The Mature Stage performers were expected to exhibit

Table 8

Mean Hip and Knep Joint Angles (Dggrees) at Maximum Backswing for the Basic

and Mature Stages

 

 

 

Basic Mature
Hip (M88) 175 169 Standard Ball
172 171 Micro-Soccer Ball
Knee (M88) 135 144 Standard Ball
130 141 MicroSoccer Ball
Stage Basic Mature
Standard
Ball 1750 169°
135° 144°
Micro-Soccer 1720 1710
Ball
130° 141°

Figure 11. Mean hip and knee joint angles at maximum backswing for Basic and Mature

Stages.

_ 76
greater hip hyperextension than the Basic Stage performers. Instead, the Mature Stage

performers’ mean hip position was flexed more at maximum backswing than the mean
hip position of the Basic Stage performers (Table 8, Figure 11). Although the magnitude
of knee flexion was not specified for the Basic and Mature Stages, the mean positions of
the knee for the Basic Stage performers for both ball types was flexed more than that of

the Mature Stage performers as illustrated in Figure 12.

 

180

 

 

 

 

 

 

 

I

l

175 l» e\

1701 H \‘3

185 ..

150 -- _

155 .. +Hip (Standard) 1 ‘

1501» l-i-HipIMlao) 1 ;
. i—a—Knee(Stendatd)|
' Deg. ‘45 ** I—tt—kneusmndaml
f 140 ..

135 .. /

130 »

125 -~

120 . .

Basic Mature
stag.

 

Figure 12. Hip and knee joint angles at maximum backswing for Basic and Mature

Stages.

In the preparatory phase for both ball types, neither stage group exhibited hip
hyperextension, and both stages exhibited knee flexion. It appeared that there was an
inverse relationship between hip and knee joint angles and stage during the preparatory

phase. That is, the Basic Stage subjects had greater hip extension and greater knee

, 77
flexion than did the Mature Stage subjects. A possible explanation of the difference

between the Basic and Mature Stages was in the relative length of the moment arm of the
combined segments (thigh and shank). For example, together, the Mature Stage subjects’
knee and hip joint flexion angles could have resulted in a shorter length of the moment
arm relative to the hip than the Basic Stage subjects’ moment arm length. Given the
same amount of strength and power, the shorter moment arm would have enabled the
Mature Stage subjects to swing the kicking leg faster initially, than the Basic Stage
subjects. The generation of segmental velocities related to a shortened moment arm was
outside the scope of this study. As stated previously, it is possible that the subjects did
not exert a maximum effort during their approach; therefore, the leap during the last
approach step potentially may not have been as dynamic, which could have resulted in a
slightly flexed hip. Additionally, trunk flexion or anterior pelvic tilt caused by lumbar
hyperextension also could have occurred which would result in the hip appearing to be
hyperextended. It was beyond the scope of this study to evaluate trunk flexion or pelvic
involvement during a kick, but relative positioning of these body parts could affect the

perception of the thigh position relative to the trunk.

Contact phase

Another of the predicted characteristics established for Basic Stage performers
during the force production phase, was that knee extension would occur as hip flexion
occurred. This relationship of knee extension during hip flexion was not found with

either ball. Instead, as hip flexion occurred, knee flexion occurred for both the Mature

78

and Basic Stage performers as illustrated in Table 9 and Figure 13. The relative

differences between maximum backswing and contact for the Basic and Mature Stage

performers were also determined (A Deg, Table 9). The Mature Stage performers

exhibited slightly less hip flexion from maximum backswing to contact and a greater

difference in knee flexion fiom maximum backswing to contact than did the Basic Stage

performers (Table 9 and Figure 13).

Table 9

Basic and Mature Stage Knee and Hip Joint Angles (dggrees) at Contact with a

Standard Youth Soccer Ball (Micro-Soccer Ball)

 

 

MBS FBC A Deg
Hip Joint (Dgg)
Stage
Basic 175 (172) 153 (150) .22 (-22)
Mature 169 (171) 150 (152) -19 (20)
Knee Joint (DQ)
Stage
Basic 135 (130) 100 (94) -34 (-35)
Mature 144 (141) 97 (100) -47 (41)
Stage Basic Mature
Standard 1530 1500
Ball 1000 97
Micro-Soccer
Ball 150° 152°
94 100

Figure 13. Mean hip and knee joint angles at contact for Basic and Mature Stages.

7 9
The principle of summation of forces was not supported by the findings of this

study, as flexion at the hip joint with subsequent flexion at the knee joint was found. For
the summation of forces principle to be followed, hip flexion followed by knee extension
would be required. What was found was, the segmental relationship of the forward
movement of the thigh (flexion at the hip joint), caused the shank to rotate posteriorly
(flexion at the knee joint). These findings further supported the work by Glassow and
Mortimer (1968) and Putnam (1983 and 1993). The resulting knee flexion may be
exhibited in order for the performer to take advantage of the stretch reflex of the muscles
involved in the movement.

The predictions that a Basic Stage performer would exhibit increasing thigh and
shank velocities until ball contact were supported by these data Illustrated in Table 10
were the mean angular velocities of the shank, and thigh of the Basic Stage subjects for
both ball types used. For the standard ball, the shank angular velocity increased by 1019
deg/sec from maximum backswing to contact, while a smaller increase of 82 deg/sec was
found for the Micro-Soccer ball. Additionally, the thigh exhibited a similar relationship
as the shank, as it increased in velocity from maximum back swing to contact by 621
deg/sec, while an increase in velocity of 554 deg/sec was found for the Micro-Soccer ball

(Table 10).

80

Table 10

Sggment Velocgy' for Basic Stage Performers with a Standard Youth Soccer Ball

Micro-Soccer Ball

 

MBS FBC A
Angular
Velocity (deg/sec)
Shank -348 (240) 671 (582) 1019 ( 822)
Thigh -48 (0) 572 (554) 621 (553)

 

For the Mature Stage performers using the standard ball, thigh angular velocity
did not decrease from maximum backswing to ball contact. Instead, the increase in
shank angular velocity to contact was greater than that of the thigh (Table 11). The same
subjects using the Micro-Soccer ball exhibited a similar shank-thigh relationship as with
the standard ball, but the magnitude of increase was greater (Table 11). This greater
magnitude in angular velocity was believed to be as a result of the lighter weight Micro-
Soccer ball. Further inspection of the results with both ball types confirmed the
movement of the shank relative to the thigh; as the shank for the Mature Stage performer
exhibited an acceleration, the thigh decelerated (Table 11). The deceleration of the thigh,
relative to the shank has been described as the soccer paradox. Although not predicted,
the Basic Stage subjects did exhibit a segmental relationship where the thigh decelerated
as the shank accelerated (Table 11). It was the opinion of this researcher that the Basic

Stage performers’ segmental relationship was an elementary form of the soccer paradox.

81
The Mature Stage subjects had greater differences in magnitudes between the thigh and

shank accelerations, than did the Basic Stage subjects. It is this greater difference in
magnitudes between the shank and thigh acceleration that highlighted the Mature Stage
performers’ skill level when compared to that of the Basic Stage performers. The Mature
Stage performers were more capable of utilizing the segmental relationships as compared
to the Basic Stage performers to produce greater velocities and accelerations because of
better timing and coordination.

Also indicated in Table 11, was that the shank velocity of the Mature Stage
subjects at contact was greater for the Micro-Soccer ball than for the standard ball.
Additionally, the acceleration of the shank and deceleration of the thigh was greater for
the Micro-Soccer ball. The Basic Stage performers did not exhibit as great a difference in

magnitudes between the ball types as the Mature Stage performers did.

Table 11

Velocig and Acceleration for Basic and Mature Stage Subjects at Contact
Using a Standard Youth Soccer Ball (Micro-Soccer Ball)

Stage Basic Mature
m
Velocity (deg/sec)
Shank 671 (582) 805 (1056)
Thigh 572 (554) 602 (537)

Acceleration (deg/secz)

Shank 7667 (8237) 6210 (8172)
Thigh 4369 (-2095) -7489 (-8393)

 

82

A number of the predicted trends at contact were found during an angled

approach. The comparison between the Basic and Mature Stage performers’ respective

shank and thigh mean thigh angular velocities are illustrated further in Figure 14. The

Basic Stage performers’ results showed increasing angular velocities of the thigh and

shank fi'om backswing to contact. The Basic Stage performers exhibited similar

velocities for the thigh and shank with the Micro-Soccer ball but had a greater shank

angular velocity with the standard soccer ball. The Mature Stage performers had a

greater difference in magnitude between the angular velocities of the thigh and shank

when compared to the Basic Stage findings. Additionally, it is evident in the illustration

of Figure 14, that the shank angular velocity of the Mature Stage subjects was greater

with the Micro-Soccer ball than with the standard soccer ball.

 

1100

 

1000 i
900 I-

800 1-

Deg/Sec

700 ..

600 1-

500 ..

 

 

 

—e—Shank (Standard Ball) i X
+Shank(Mlcro-SoooerBall) ‘
+Thigh (Standard Ball) I 1
+Thigh(Micro-SocoerBall)l ‘

 

 

 

400

fi

Basic

Mature

 

Figure 14. Basic and Mature Stage subjects’ thigh and shank angular velocities at contact

with the standard and Micro-Soccer balls.

83
Although the mean thigh velocities of the Mature Stage performers for both ball

types was comparable to the Basic Stage mean thigh velocities, the Mature Stage subjects
exhibited greater mean shank velocities relative to thigh velocities. Additionally, the
angular velocity for the thigh of the Mature Stage subjects decreased when using the
Micro-Soccer ball; perhaps explaining the sharp increase in magnitude of the shank
angular velocity. These greater differences between thigh and shank velocities would
have been expected for the Mature Stage, confirming the segmental relationship as
discussed by Putnam“ (1993) and Glassow and Moritrner (1968). This difference between
segmental velocities further highlighted the skill level difference associated with the two
stages.

Both the Mature Stage and Basic Stage performers exhibited knee joint flexion at
contact for both ball types. There may be other variables, such other body segment
interactions, that could differentiate between skill levels during an angled approach kick.
For example, arm and leg opposition, was a characteristic used to differentiate between
skill levels in the study by Haubenstricker et al. (1981). It was outside the scope of this

study to examine the relationships of other body segments to kicking.

Follow through phase

It was expected, and confirmed, that for the Basic Stage performers, knee flexion
was maintained during the follow through phase as hip flexion occurred for both soccer
ball types used. The Mature Stage performers exhibited greater hip flexion with the

standard ball at 123° in comparison to 128° with the Micro-Soccer ball. The hip flexion

84 -
of the Basic Stage performers was greater than that of the Mature Stage performers, but

almost identical for both ball types used. The differences in hip joint angles between the
Basic Stage and Mature Stage was likely a result of greater segmental velocities of the
Mature Stage performers. All performers were found to extend the knee to approximately
176° with both ball types during the follow through phase. It was expected and found in
the results that as skill level increased, the Mature Stage level subjects exhibited marked
increase in hip flexion, and approached full extension of the knee joint. The cause of the
greater hip flexion was most likely due to the increased segmental velocities throughout
the kicking sequence. The increased segmental velocities of the Mature Stage subjects
would result in increased momentum of the segments, causing marked flexion of the hip
joint during follow through . The hip joint angles at follow through further differentiated
the stages for the angled approach for both ball types. Finally, for both ball types, all of
the Mature Stage performers were airborne during the follow through phase while the
Basic Stage performers were not. Figure 15 provided an illustrated overview of the
relationship between the hip and knee joints of the Basic and Mature Stage subjects at

maximum forward movement.

85
Stage Basic Mature

Standard 1370 If
Ball 17 60
17K
Micro-Soccer 1380 1230
Ball
17% 1770

Figure 15. Mean hip and knee joint angles at maximum forward movement for Basic and
Mature Stages.

Segment timing and coordination

The results of the current study revealed a difference in the timing and
coordination of the shank and thigh. The expected segmental relationship, or the soccer
paradox, between the thigh and shank of a randomly selected Mature Stage subject is
illustrated for both a standard youth soccer ball and the Micro-Soccer ball in Figure 16
and 17, respectively. From maximum backswing of the kicking leg (MBS), both the
thigh and the shank increased in velocity, as illustrated by the increase in the slopes of the
curves (Figure 16). This increased velocity of both segments corresponded to the initial
force production phase of the kick. As the velocity of both segments increased, at 0.034
sec prior to contact (frame 21), the thigh reached its peak velocity and began decreasing

in velocity, as indicated by the downward sloping curve.

86

 

 

2000

1000 ~~

I 1500 ”

MBS I MFM

I e
y ... y

‘-

 

  

 

A
T T v-.-v r

A

FBC

1e 21 23 25 27 29 31 33"

 

 

Figure 16. Mature Stage performer shank and thigh relationship using a standard youth

soccer ball.

Frame

Segment Angular Velocity

 

.l '—O'— R.SHANK Segment angular
I Velocity 0091800

I
I

j ------ amen Segment angular
. Velocity Deglaec
I Frame time t .017 sec

 

MBS - Maximum Backswing
FBC - Contact

MFM - Maximum Forward Movement

 

 

2000

1500 t»

1000 ,,

 

 

-1 OOO

 

 

 

Frame

Segment Angular Velocity

 

! —o— R.SHANK Segment angular
1 Velocity Deg/sec

Frame time = .017 sec

 

MBS - Maximum Backswing
FBC - Contact

MFM - Maximum Forward
Movement

 

Figure 17. Mature Stage performer shank and thigh relationship using a Micro-Soccer

ball.

87
At contact (FBC), the thigh continued its decrease in velocity, while the shank

continued increasing in velocity. This increase in shank velocity continued for 0.034 sec
(3 flames) following contact. At that time, flame 26, the shank reached its peak and
decreased in velocity until maximum forward movement. A slight increase in thigh
velocity began in follow through at flame 29.

This slight increase in velocity for the thigh indicated that the momentum of the
shank caused the thigh to increase in velocity during the follow through. At maximum
height of the kicking foot (MF M), the velocity of the thigh and shank both reached
approximately zero deg/sec, indicating the end of force dissipation.

The reader is directed to Figure 17, where thigh and shank relationships for 8
Mature Stage performer with the Micro-Soccer ball are illustrated. At maximum
backswing (MBS), the thigh increased in velocity while the shank decreased. This
decrease in shank angular velocity occurred for approximately 0.017 seconds (one flame)
past maximum backswing, followed by an increase in velocity that lasted past contact.
Approximately 0.034 seconds (two frames) prior to contact, the thigh began to decrease
its velocity. The shank however, continued increasing in velocity to and through contact,
by one flame, as illustrated by the increasing slope of the curve flom contact (F BC) to the
peak velocity for the shank. The thigh reached its post contact minimum velocity at
approximately frame 22, .034 seconds (two flames) after peak velocity of the shank. It
was at flame 23 that a second increase in velocity of the thigh was noted. This secondary
increase in velocity, was not as pronounced with the angled approach using the standard

ball, as with the Micro-Soccer ball. This secondary increase in velocity (Figure 17) of the

88
thigh was thought to be the result of the momentum of the shank causing the thigh to

make a spatial adjustment as a result of the airborne portion of the follow through phase.

At contact, the shank velocity was approximately 850 deg/sec using the standard
youth soccer ball (Figure 16), while for the Micro-Soccer ball it was approximately 1700
deg/sec (Figure 17). This 850 deg/sec difference in velocity at contact could explain the
secondary increase in velocity of the thigh during the follow through phase. The shank
had a greater amount of momentum which caused the anterior rotation of the thigh, seen
as an increase in hip joint flexion, during follow through. This relationship, which was
found for the Mature Stage subjects, indicated a more mature pattern as predicted by the
current study and as was discussed by Putnam (1991 and 1993) and Glassow and
Mortimer (1968).

Additionally, one must consider that less force was needed to overcome the
resting inertia of the Micro-Soccer ball than the standard soccer ball, since the Micro-
Soccer ball weighed 26% less than the standard soccer ball. With weight and mass being
proportional, the 850 deg/sec difference at contact in the shank angular velocities between
both soccer balls, also could have been attributed to the difference in inertia of each
respective ball.

The following predicted trends for the angled approach were found in the current
study for both ball types. As predicted, during the preparatory phase, the Basic Stage
performers placed the foot of the support leg along the angled approach line, while the
Mature Stage performers placed their support foot along the path of the intended flight of
the ball. This foot placement assisted in differentiating between the two skill levels.

Additionally, no hip hyperextension was found for either stage, and the knee of the

89
respective kicking legs was flexed at maximum backswing. At contact, the Basic Stage

performers exhibited increasing angular velocities of the thigh and shank, as predicted.
The Mature Stage performers exhibited the segmental relationship (soccer paradox),
where the thigh decreased in velocity while the shank continued to increase in velocity
just prior to contact. The Basic Stage performers also exhibited similar actions that could
be characterized as an elementary form of the soccer paradox. Knee flexion was found at
contact for both stages. The knee was almost fully extended at maximum forward
movement for all performers. Also, the Mature Stage subjects exhibited greater hip
flexion at maximrun forward movement and maintained knee flexion during the follow
through phase than the Basic Stage, subjects as predicted. Finally, as predicted, all of the

Mature Stage subjects were airborne during the follow through phase.

Segment rotation differences between stages three and four

The theories pertaining to segmental relationships developed by Putnam (1993)
were based on adult athletes. One purpose of this study was to identify differences in
rotations of the thigh, as well as the shank, of the kicking limb between subjects
exhibiting stages three and four while kicking a standard youth soccer ball. In the current
study, it was hypothesized that the stage four subjects would exhibit a more mature
pattern with the kicking limb than the stage three subjects. From the literature, this more
mature pattern would be indicated by rotation of the thigh dominating the initial part of
the force production phase with minimal rotation about the knee joint. Furthermore, in

the later phase of the force production phase, thigh rotation would decrease as shank

9O
rotation increased to ball contact. The statistical method employed to determine

significant differences was a balanced design analysis of variance (ANOVA, p < .10).
The selected kinematic variables of mean angular velocities and mean angular
accelerations of the shank and thigh, for the stage three and stage four performers were
compared against each other in order to determine if significant differences existed
between the variables tested. There were no significant differences at maximum
backswing between stages three and four in the variables of angular velocity and
acceleration for the thigh, as well as the shank (Table 12). At maximum backswing the
thigh may have stopped prior to beginning its forward movement or may have just begun
its initial forward movement, whereas the shank would have stopped or finished its
flexion. Therefore, if this period were truly maximum backswing, there should be no
significant difference, even though the thigh angular velocities and accelerations were not

at zero.

. 91
Table 12

ANOVA: Stage Effect on Mean Angular Velocity and Mean Angular Acceleration for Stage Three
and Four Subjects at Maximum Backswing

Analysis of Variance for Angular Velocity of the Shank

Source DF SS MS F P
Stage 1 40986 40986 1.66 0.218
Error 14 345358 24668

Total 15 386344

Analysis of Variance for Angular Velocity of the Thigh

Source DF SS MS F P
Stage 1 10936 10936 0.79 0.389
Error 14 193898 13850

Total 15 204834

Analysis of Variance for Angular Acceleration of the Shank

Source DF SS MS F P
Stage 1 205028 205028 0.010.906
Error 14 20039588714313992

Total 1 5 200600915

Analysis of Variance for Angular Acceleration of the Thigh

Source DF SS MS F P
Stage 1 22021668 22021668 1.72 0.211
Error 14 179086457 12791890

Total 15 201108125

p < .10

 

At ball contact, the stage four performers were found to be significantly different
flom the stage three performers with respect to angular velocity of the shank (F = 7.28,
p = .017) and the angular acceleration of the thigh (F = 12.38, p = .003). There was not a
significant difference in the angular velocity of the thigh (F = .26, p = .615), nor in the
angular acceleration of the shank (F = .83, p = .377) between the stage three and four

subjects (Table 13).

92
Table 13

ANOVA: Stage Affect on Angular Velocity and Acceleration at Contact
Analysis of Variance for Angular Velocity of the Shank

 

Source DF SS MS F P
Stage 1 730298 730298 7.28 0017’
Error 14 1404893 100349

Total 15 2135191

Analysis of Variance for Angular Velocity of the Thigh
Source DF SS MS F P

Stage 1 3994 3994 0.26 0.615

Error 14 211701 15122

Total 15 215695

Analysis of Van'ance for Angular Acceleration of the Shank
Source DF 88 MS F P

Stage 1 20322515 20322515 0.83 0.377
Error 14 341 105499 24364679

Total 15 361428014

Analysis of Variance for Angular Acceleration of the Thigh
Source DF SS MS F P

Stage 1 87719146 87719146 12.38 0003*
Error 14 99203397 7085957

Total 15 186922544
*p < .10

The stage four subjects’ significantly greater shank angular velocity and
significantly greater deceleration of the thigh at contact highlighted their increased skill
level in comparison to the stage three subjects. The significant differences found in the
angular velocities of the shank as well as angular accelerations of the thigh at contact
indicated that the stage four subjects were better able to utilize the segmental
relationships in performing the kick resulting in a more coordinated pattern. This
explanation does agree with the discussions of segment coordination by Putnam (1983)

and Glassow and Mortimer (1968). The significant differences found between angular

93
velocity of the shank and angular acceleration of the thigh for stages three and four

subjects using a direct approach, may be a result of increased coordination and timing
over the less mature stage three subjects.

A comparison between the rotations of the shank, as well as the thigh, during the
follow through phase indicated a significant difference in the shank angrlar velocity
(F = 6.41, p = .024) and the thigh angular velocity (F = 6.16, p = .026) between stages
three and four (Table 14). The stage four subjects exhibited decreasing velocity of the
shank, indicating knee flexion, and increasing thigh velocity, indicating hip flexion. In
contrast the stage three subjects exhibited increased shank velocity, indicating knee
extension, and a decrease in thigh angular velocity, indicating less hip flexion. These
differences in velocities were probably a result of the stage four performers being
airborne at maximum forward movement of the kicking foot, which would require
different spatial adjustments to be made relative to the stage three subjects. While the
stage four subjects were airborne, the length of the leg moment arm may have required
adjustment for the purpose of balance and timing. However, examining the moment arm

length relative to balance of the body was outside the scope of this study.

94
Table 14

ANOVA: Stage Effect on Angular Velocgy' and Acceleration at Maximum Forward Movement

Analysis of Variance for Angular Velocity of the Shank

Source DF SS MS F P
Stage 1 108455 108455 6.41 0024*
Error 14 236969 16926

Total 15 345424

Analysis of Variance for Angular Velocity of the Thigh
Source DF SS MS F P

Stage 1 48819 48819 6.16 0026*

Error 14 1 10966 7926

Total 15 159785

Analysis of Variance for Angular Acceleration of the Shank
Source DF SS MS F P
Stage 1 320582 320582 0.02 0.893
Error 14 238990453 17070747

Total 15 23931 1035

Analysis of Variance for Angular Acceleration of the Thigh
Source DF 88 MS F P

Stage 1 4031562 4031562 0.81 0.384

Error 14 69751394 4982242

Total 15 73782956
‘p < .10

The hypothesis that there would be significant differences in the rotations
of the thigh as well as the shank of the kicking limb between subjects exhibiting stages
three and four while kicking a standard youth soccer ball using a direct approach was
rejected. A comparison between stages three and four with respect to relative angular
velocities and accelerations was provided in Table 15. Significant differences between
stages three and four were found only with respect to the angular velocity of the shank at
contact and angular acceleration of the thigh at contact. Also, significant differences

were determined with respect to angular velocity of the shank at maximum forward

95
movement, and angular velocity of the thigh at maximum forward movement. The

significant differences between stages three and four indicated the higher skill level of the
stage four subjects with respect to the angular velocity of the shank and angular
acceleration of the thigh. The significantly greater shank angular velocity and lower
thigh angular acceleration at contact are in accordance with the literature pertaining to

skilled kickers.

Table 15

Angular Velocig and Acceleration Comparisons Between Stage Three and Four

 

 

 

Stage 3 Stgge 4
Maximum Backswing
Shank 0) >0)
Thigh a) <0)
Shank or >01
Thigh 01 >01.
Contact
Shank 0) >0) *
Thigh 0) <0)
Shank or <01
Thigh a <01 1-
Maximum Forwgg Moveme_pt
Shank 0) <0) 1'
Thigh 0) >0) *
Shank a or (0) = angular velocity)
Thigh or <a (a = angular acceleration)
*p < .10

When the segmental angular velocities were examined graphically, (Figures 18
and 19) a timing difference seemed to exist between stage three and stage four

performers. For discussion purposes, one data set for angular velocity and acceleration

96

 

 

Segment Angular Velocity

 

__~___.__..__.__-__._._J

I—O—R.SHANK SegmentAngular I
I Velocity Deg/sec l 3
' I

I ------- R.THIGH SegtmntAngular
Velocity Deg/sec l :

I Frame time a .017 sec

 

 

MBS - Maximum Backswing

FBC - Contact

 

 

 

MFM - Maximum Forward
Movement

 

I. ._-_____ _.-___u__._ .fiz.“

 

Figure 18. Stage three performer using a direct approach while kicking a standard youth

soccer ball.

 

 

1400 Segment Angular Velocity f

 

' —o— R.SHANK Segment angular ‘ .
I Velocity Deg/sec E I

    

I ....... R.THIGH Segment angular . i
Velocity Degleec I I

”It”; i .. a ~ . "zit I Frantetlmecmrsec g
171921232527253135 'I
j ‘ ’ MBS - Maximum Backswing i

FBC MFM FBC ' 00111801

 

 

MFM - Maximum Forward
Movement

 

 

 

Frame

 

Figure 19. Stage four performer using a direct approach while kicking a standard youth

soccer ball.

_ 97
were randomly chosen flom each stage three and stage four data sets. A stage three

subject’s data for kicking is illustrated in Figure 18. At maximum backswing (MBS), the
thigh is shown to be increasing in angular velocity, whereas the shank is shown to be
decreasing in velocity. The decrease in the shank angular velocity may have indicated
that the timing of forward movement of the thigh caused the shank to rotate posteriorly
resulting in knee flexion (Putnam, 1993). At approximately flame seven, both the thigh
and shank were increasing in velocity toward contact. At 0.017 seconds (one flame) prior
to contact (Figure 18, flame 11), the thigh reached its peak velocity and began to decrease
in velocity. The shank continued its increase in velocity up to and following contact for
0.034 seconds (two flames), before beginning its decrease in velocity. From the peak
angular velocity of the shank (Figure 18, flame 14), both the shank and the thigh
decreased in velocity to maximum forward movement of the kicking foot (MF M). The
maximum forward movement indicated the end of the kicking sequence for the stage
three subject. At that point, (MFM), the thigh appeared to have a constant velocity for
0.017 seconds (one flame), while the shank continued its decrease in velocity.

The data for a stage four subject, illustrated in Figure 19, shows increasing thigh
as well as shank velocities flom maximum backswing to 0.051 seconds (three flames)
prior to contact, where the thigh segment peaked in velocity (flame 18). Then the thigh
began to decrease in velocity (Figure 19, flame 19), while the shank continued to increase
in velocity for 0.068 seconds (four flames) one flame past contact, as the thigh decreased
in velocity. The decrease in thigh velocity with an increase in shank velocity was
representative of the soccer paradox. Thigh velocity decreased for 0.068 seconds (four

frames) following contact, before increasing in velocity. The secondary increase in

98
velocity found for the thigh (flame 26) of the stage four subject in Figure 19, was also

seen in the stage three subject. This secondary increase most likely resulted because of
the increased angular velocity of the shank following contact. The stage four performer
made a spatial adjustment while being airborne during the follow through phase. After
shank peak velocity, the shank decreased in velocity for 0.119 seconds (seven flames) to
maximum forward movement. At the end of the kicking sequence (MF N0, the thigh was
at its secondary peak and the shank was decreasing in velocity at maximum forward
movement.

The stage three performer in Figure 18 exhibited a shorter period of time from
maximum backswing to contact (0.136 sec) than did the stage four performer in Figure 19
(0.17 sec). The force production phase of the stage four performer occurred over a
greater time period than for the stage three performer, in which the leg segments
accelerated forward prior to ball contact, resulting in the distal segment reaching a greater
velocity at ball contact (1200 deg/sec) than did the stage three performer (800 deg/sec).
The Mature Stage subject’s shank was already increasing in velocity at maximum
backswing, unlike the Basic Stage subject where it was decreasing in velocity. This
difference in timing may have been as a result of the Basic Stage subject’s shank
“lagging” behind the forward movement of the thigh. The segmental relationships were
found in the stage three and four performers. The soccer paradox exhibited by the stage
four subjects at contact can be explained by the momentum of the shank. The segmental
relationship exhibited in the current study coincided with the concepts as discussed by
Putnam (1983 and 1993). A final difference was that maximum thigh velocity occurred

closer to contact (0.017 sec, one flame) for the stage three performer than for of the stage

99
four performer (0.051 sec, three flames). This likely indicated that the stage four

performer’s coordination of the segments was more skilled.

The angular acceleration data, for the same stage three performer and stage four
performer used in Figures 18 and 19, are illustrated in Figures 20 and 21. At maximum
backswing, the stage three performer showed an increase in thigh angular acceleration
and a decrease in shank acceleration. This acceleration of the thigh lasted approximately
0.034 seconds (two flames) while deceleration of the shank lasted approximately 0.017
seconds (one flame) following maximum backswing. At flame six, the thigh of the stage
three performer began to decelerate, and continued decelerating four flames past contact.
During the thigh deceleration the shank continued to accelerate to 0.017 seconds (one
flame) prior to contact. Relatively large accelerations were illustrated in Figure 20 flom
flame six to flame eight for the stage three subject and were exhibited by the steep slope
between the flames. The large magnitude in the shank acceleration was attributed to a
rapid knee extension flom maximum backswing to ball contact. At contact, both the thigh
and the shank were decelerating. Also noted, was the fairly rapid deceleration of the
shank following contact flom flame 12 to flame 14 (Figure 20) seen as steep negative
slopes.

Even though the graph of angular velocity (Figure 18, flame 12) showed an
increase in shank velocity prior to contact, the rate at which the velocity was changing
was not as great as the preceding flame. This relatively smaller rate of change of velocity
resulted in the deceleration of the shank. Rapid decelerations at contact were due

primarily to overcoming the inertia of the ball at contact.

100

 

 

 

 

 

 

 

25000 :
Segmental Angular Acceleration I
i
15000 r I
10000 (I ., .-- I—o— R.SHANK Segment angular T I
,9 Acceleration Degteecleec I .
500° " I I R THIGH Segmentangular I I
. ,- l """" ‘ ‘ l
Degteecleeco m , ‘ .‘ Acceleration Deg/cedeec I I
‘ A4 a I Frame time 8 .017 sec .
.5000 . MBS - Maximum eacltswing
l
- . F - f
10000 MBS BC Contact I

 

 

Ffllll.

Movement

Figure 20. Angular acceleration of the thigh and shank of a stage three performer using a

 

 

 

 

 

 

 

 

   

 

 

 

standard youth soccer ball.
25000
Segmental Angular Accelerations
20000 ‘-
15000 «~
100001: I—o—RSHANKSegmentangular I i
5000 ._ l I
.---.. .. l ------- R.THIGHSegmentangular I
OW.” ,0 ' " I . Acceleration Degteedeec
O :o y I. : - :. Vtatr; I Frametimes.017eec
l357 111315171921
.5000 .l j . MBS - Maximum Backswing
.10000 .. M88 '2‘- FBC - Comet
_1 5000 F30 MFM - Maximum Forward
Movement
Frame

 

Figure 21. Angular acceleration of the thigh and shank of a stage four performer using a

standard youth soccer ball.

101
Following contact, a deceleration of the shank continued to maximum forward

movement of the foot. The thigh began a secondary acceleration, after contact at flame
15, which was approximately 0.068 seconds (four flames) after the peak angular
acceleration of the shank. The secondary acceleration of the thigh (Figure 20, flame 15)
was accompanied by a brief, relatively constant acceleration of the shank (Figure 20,
flames 15 through 17). The momentum of the shank, was probably responsible for the
thigh accelerating to the position of maximum forward movement of the kicking foot
(flame 19 of Figure 20).

The acceleration data for the stage four subject previously examined, is illustrated
in Figure 21. A different timing of accelerations and decelerations for the segments was
exhibited. From maximum backswing (MBS) to peak angular acceleration of the thigh
(0.085 seconds, five flames), the thigh and shank both accelerated. At flame 16 of Figure
21 , the thigh peaked and then began to decelerate, as the shank continued accelerating to
its maximum angular acceleration for an additional 0.034 seconds (two flames).

At contact (F BC), the thigh had reached its greatest deceleration, as the shank
continued decelerating (flame 21, Figure 21). Following contact, the shank continued its
deceleration for 0.102 seconds (six flames), as the thigh accelerated for approximately the
same period of time. From approximately flame 27 of Figure 21 , the thigh decelerated
for 0.034 seconds (two flames), while the shank accelerated for the same period of time.
The changes in shank acceleration flom flame 27 to the end of the kicking sequence at
maximum forward movement of the kicking foot, were potentially due to a spatial
adjustment while the stage four performer was in flight. Shortening of the relative

moment arm of the kicking leg during the airborne stage of the follow through may have

102
resulted in acceleration of the shank. The specific timing of this adjustment was not

studied in the current investigation.

Deceleration of the thigh for the stage three subject occurred over a longer period
of time (0.153 seconds) than did the deceleration of the thigh of the stage four subject
(0.085 seconds) flom peak angular acceleration. The magnitude of the stage three
subject’s deceleration (Figure 20, flames 6 to 12) was greater (22,426 deg/secz) than that
of the stage four subject’s deceleration (18,598 deg/secz, flames 16 to 21). The difference
in the time periods and magnitudes of deceleration can be attributed to the increased
coordination and timing of the stage four subject, which caused the performer to become
airborne. The greater rate of deceleration of the thigh prior to contact exhibited by the
stage four subject compared with the stage three subject, could have been because the
stage four subject was airborne. Once airborne, in the follow through phase, the stage
four performer needed to position the kicking leg for landing. As in Haubenstricker et al.
(1981) and Barfield ( 1995), if the momentum of the subject is sufficient enough
following contact, the result may be an airborne phase and the subject may land on the
kicking foot, instead of the support foot. The ability to land on the kicking foot further
differentiated between more advanced skill levels. In the current study, none of the stage
three subjects landed on the kicking leg foot.

At contact, the thigh of the selected stage four performer was seen to exhibit the
characteristic of thigh deceleration prior to contact found in the literature for skilled
kickers (Putnam, 1993; Glassow and Mortimer, 1968). The stage four performer
exhibited greater thigh deceleration closer to contact (Figure 21, flames 16 to 21) than did

the stage three performer (Figure 21, flame 6 to 12), illustrated by the steeper negative

. 103
slope for the stage four subject. This difference in thigh deceleration, was attributed to

the differences in the peak angular velocities of the stage four subjects which resulted in
increased momentum of the shank. According to Putnam (1993) the greater momentum
of the shank caused a greater deceleration of the thigh for the stage four subject at contact

due to a more ballistic movement of the shank.

Direct approach versus angled approach

The angled approach observed in skilled soccer players was approximately 45° to
the ball (Douge, 1988; Isokaw and Lees, 1988). Researchers who studied the angled
approach (Plagenhoef, 1971; Isokawa and Lees, 1988; Barfield, 1995) indicated that an
angled approach resulted in increased performance when compared to a direct approach.
This increased performance was measured by higher ball velocity and angle of ball
projection following contact. The higher ball velocity was caused by the pelvis and leg
being carried through a greater range of motion. These greater ranges of motion allowed
for the development of increased leg segment velocities. The greater range of motion of
the angled approach involved a greater number of muscle groups due to preparatory
movements of the hip joint and pelvic girdle. The increased number of muscle groups
and greater ranges of motion contributed to increased muscle forces which can result in
increased segment velocities and subsequent higher ball velocities. However, literature
relating to children’s performance of a kick during the developmental years, or to
segmental differences using an angled approach has not been found. One purpose of this

study was to determine if significant differences existed in the shank, as well as the thigh,

104
angular velocities and accelerations for subjects, between a direct approach and an angled

approach while kicking a standard youth soccer ball. It was hypothesized that there
would be significant differences in rotations of the thigh, as well as the shank of the
kicking limb of the subjects using a direct approach when compared with subjects using
an angled approach, while kicking a standard youth soccer ball.

The angular velocities and accelerations for the thigh, as well as the shank, of
performers using direct and angled approaches were treated statistically with a balanced
design AN OVA (p < .10). The three points of interest in the kick, maximum backswing,
contact, and maximum forward movement were analyzed. The differences between the
two approaches with respect to shank angular velocity were not significantly different at
maximum backswing (F = .05, p = .825; Table 16). In addition, thigh angular velocity
comparisons between the direct approach and the angled approach were found not to be
significantly different (F = .17, p = .687). Moreover, the differences between the two
approaches with respect to the angular accelerations of the shank segment were found not
significant (F = .60, p = .446). Finally, the differences between the two approaches with
respect to angular acceleration of the thigh were found not significant (F = .01, p = .917).
As a result of the current study, the angular velocities and accelerations of the shank and
thigh at maximum backswing were found to be not significantly different between the
direct approach and the angled approach.

At maximum backswing, the thigh may have almost stopped prior to beginning its
forward movement or may just have begun its initial forward movement. At maximum

backswing, the shank would have been finishing its motion. Therefore, if this period

105
were truly maximum backswing, there should be no significant differences, even though

the thigh and shank angular velocities and accelerations were not zero.

Table 16

ANOVA: Approach Effect on Angular Velocgy' and Angular Acceleration for the Thigh and Shank
at Maximum Backswing

 

Analysis of Variance for Angular Velocity of the Shank

Source DF SS MS F P
Approach 1 1426 1426 0.05 0.825
Error 30 858934 28631

Total 31 860360

Analysis of Variance for Angular Velocity of the Thigh

Source DF SS MS F P
Approach 1 2198 2198 0.17 0.687
Error 30 397494 13250

Total 31 399691

Analysis of Variance for Angular Acceleration of the Shank

Source DF SS MS F P
Approach 1 24522930 24522930 0.60 0.446
Error 30 1234673665 41155789

Total 31 1259196595

Analysis of Variance for Angular Acceleration of the Thigh

Source DF SS MS F P
Approach 1 119353 119353 0.010.917
Error 30 323005647 10766855

Total 31 323124999

 

p<.10

At ball contact, only the angular acceleration of the shank was found significantly
different (F = 4.45, p = .043) between the two approaches. In contrast, there were no

significant differences between the two approaches with respect to the angular velocities

106
of the shank and thigh, nor angular acceleration. These AN OVA results are reported in

Table 17.

Table 17

ANOVA: Approach Effect on Angular Velocig and Angular Acceleration for the Thigh and Shank
at Contact

 

Analysis of Variance for Angular Velocity of the Shank

Source DF 88 MS F P
Approach 1 15891 15891 0.13 0.718
Error 30 35761 35 1 19205

Total 31 3592026

Analysis of Variance for Angular Velocity of the Thigh

Source DF SS MS F P
Approach 1 643 643 0.03 0.868
Error 30 682097 22737

Total 31 682740

Analysis of Variance for Angular Acceleration of the Shank

Source DF SS MS F P
Approach 1 162709074 162709074 4.45 0043*
Error 301097401444 36580048

Total 31 1260110519

Analysis of Variance for Angular Acceleration of the Thigh

Source DF SS MS F P
Approach 1 36924766 36924766 2.54 0.122
Error 30 43684412514561471

Total 31 473768891

 

*p<.10

The significant difference found between the approaches with respect to the
angular acceleration of the shank was likely due to greater shank acceleration caused by

the increased difficulty of the angled approach. Overall, the angular acceleration of the

107
shanks were lower for the angled approach versus the direct approach, as opposed to the

expected findings of greater shank angular acceleration due to the greater range of motion
through which the leg was carried. Even though both groups completed the angled
approach, the lack of experience using this approach by the subjects may have had an
effect on the performance of the kick. The subjects may have been concentrating more
on the task of completing the kick using the angled approach, instead of kicking the ball
as forcefully as possible.

No significant differences between the approach types were found when
comparisons were made at maximum forward movement of the kicking foot. At
maximum forward movement, because the foot would have reached its peak height, the
thigh may have almost stopped prior to beginning its backward movement or may have
begun its initial backward movement. The shank would have been stopped or finished its
extension at the knee. Therefore, if this period were truly maximum forward movement,
there should be no significant differences, even though the thigh and the shank velocities
and accelerations were not zero. The position at maximum forward movement may be
similar for any kicker in any stage, and may account for the lack of significance at
maximum forward movement. The variables of angular velocity and acceleration of the
thigh, as well as the shank, for maximum forward movement are presented in Table 18.
The hypothesis that there will be a difference in the rotations of the thigh, as well as the
shank, of the kicking limb of the subjects using a direct approach when compared with
subjects using an angled approach, while kicking a standard youth soccer ball was

rejected.

108
Table 18

ANOVA: Approach Effect on Angular Velocin and Angular Acceleration for the Thigh and Shank

at Maximum ForvvaLd Movement

 

Analysis of Variance for Angular Velocity of the Shank

Source DF 38 MS F P
Approach 1 4522 4522 0.210.647
Error 30 635079 21169

Total 31 639601

Analysis of Variance for Angular Velocity of the Thigh

Source DF SS MS F P
Approach 1 29464 29464 1.04 0.317
Error 30 853360 28445

Total 31 882824

Analysis of Variance for Angular Acceleration of the Shank

Source DF SS MS F P
Approach 1 21196398 21196398 0.96 0.335
Error 30 662350515 22078350

Total 31 683546912

Analysis of Variance for Angular Acceleration of the Thigh

Source DF SS MS F P
Approach 1 638761 638761 0.12 0.735
Error 30 163802657 5460089

Total 31 164441418

 

'p< .10

Illustrated in Table 19 was an overview of the differences between the direct and
angled approaches with respect to the angular velocities and accelerations of the shank, as

well as the thigh, for the current study.

109

Table 19

Angular Velocity and Acceleration Comparisons Between the Direct and Angled
Approach

 

Direct Angled
Maximum Backswing
Shank (0 <0)
Thigh 0) <0)
Shank 01 <01
Thigh 01 >01
Contact
Shank 0) <0)
Thigh 0) >0)
Shank or <01 *
Thigh or <01
Maximum Fonuard Movement
Shank or >to
Thigh 0) >0)
Shank 0 <0: (0) angular velocity)
Thigh or <0t (a angular acceleration)
‘p < .10

In the current study, the performers most likely experienced difficulty in
completing the angled approach due to a lack of experience with this approach. The only
variable found to be significantly different between the approaches was angular
acceleration of the shank at contact. Additionally, the angular acceleration of the shank
was less for the Mature Stage performers than for the Basic Stage performers. These
findings may be due to the inexperienced subjects concentrating on the task of

completing the kick, instead of kicking the ball as forcefully as possible.

1 10
Standard youth soccer ball versus the Micro-Soccer ball

A light weight soccer ball developed for children was used in this study. The
developers of the Micro-Soccer ball theorized that kicking performance would be
increased, as shown by increased ball velocity. The final hypothesis for this study stated
that the resultant velocity of the lightweight soccer ball would be greater than that of the
standard youth soccer ball regardless of approach. Resultant ball velocity was
determined as the initial velocity (V o) of the ball as it left the foot. A balanced design
ANOVA (p < .10) was used to test the above hypothesis.

The stage three and four subjects obtained greater initial ball velocity (V o) with
the Micro-Soccer ball at 9.03 and 14.24 m/sec, respectively. These initial velocity values
corresponded well with Luhtanen’s (1988) findings of initial velocity in his study of
children. The stage three subjects’ mean initial ball velocities differed by 1.56 m/sec
between the two ball types, whereas the stage four subjects’ mean initial ball velocities
differed by 2.57 m/sec. The actual initial ball velocities between the ball types and across

the stages used in the current study are presented in Table 20.

Table 20

Initial Ball Velocities Using a Direct Approach
Stage 1 2 3 4

 

CD

Standard Vo(mlsec) 3.46 4.12 7.46 11.66

Micro-Soccer Vo(mlsec) 3.17 4.59 9.03 14.24

111
For the angled approach, the initial velocity differences between the standard

youth soccer ball and Micro-Soccer ball, favored the Micro-Soccer ball. The difference
in initial velocities between the two ball types was .64 m/sec for the stage three
performers and 2.16 m/sec for the stage four subjects. The minimal differences in the
initial velocities (V o) of the Basic Stage subjects were likely the result of a lower skill
level than that of the Mature Stage subjects. This lower skill level is illustrated in the
velocity and acceleration graphs discussed earlier. Therefore, they may have
concentrated on the task of completing the kick and not on kicking the ball as hard as
possible. The initial velocities for the angled approach for both ball sizes and both levels

used in the current study were are reported in Table 21.

 

 

Table 21
Initial Ball Velocities Using an Angled Approach
Stage 1 2 3 4
(Basic) (Mature)
rm
Standard Vo(mlsec) * ' 8.26 10.45
Micro-Soccer Vo(mlsec) ’ ' 8.90 12.62

 

Resultant ball velocities were examined for both approaches. For both
approaches, resultant ball velocities were significantly different between the Micro-
Soccer ball and the standard youth soccer ball (F = 5.25, p = .025). The use of the light

weight ball resulted in greater initial velocities of the ball regardless of the approach used,

1 12
than for the standard soccer ball (Table 22). However, no significant difference was

found between the approach used and ball velocity (F = .45, p = .503).

 

 

Table 22

Analysis of Variance for Ball Velocigy

Source DF SS MS F P
Ball 1 497589 497589 5.25 0.025‘
Approach 1 43087 43087 0.45 0.503
Error 61 5782358 94793

Togl 63 6323035

*p < .10

Of interest, was the maximum ball velocity reported by Luhtanen (1988).
Luhtanen stated that the 9-12 year old subjects in his study obtained ball velocities of
14.90 m/sec. He used a 450 gram ball for the 9-12 year old subjects which was heavier
than the Micro-Soccer ball used in the current study, which weighed 260.93 grams. The
stage one subjects obtained a greater velocity with the standard youth soccer ball at 3.46
m/sec, compared to the Micro-Soccer ball at 3.17 m/sec. However, the stage two, three,
and four subjects obtained greater ball velocities with the Micro-Soccer ball at 4.59, 9.03,
and 14.24 m/sec, respectively. Due to the small sample size for the stage one subjects,
the greater ball velocity of the standard ball could be attributed to random variation. The
stage four performers (three to eight years of age) in the current study using a direct
approach, obtained a velocity of 14.24 m/sec, which was comparable to the 14.90 m/sec
velocity obtained for the 9-12 year old subjects used by Luhtanen. Therefore, if resultant
ball velocity were used as a performance measure, then the Micro-Soccer ball did

improve performance, and its use would be beneficial to young soccer players.

1 13
Post filming interview

The assumption was made that as a result of each performer handling the two
balls and personally placing them to be kicked, the opporttmity for gaining personal
perceptions of the ball would be standardized across the subjects. Following the kicking
trials, each performer was asked four questions about the two balls during an exit
interview (Appendix C). It should be noted, that although both balls were of a similar
color, the weights and sizes were different. The Micro-Soccer ball was larger in
circumference, but lighter than the standard youth soccer ball used in this study. When
the children were asked: What ball did they “like” to kick best, 95% of the subjects chose
the Micro-Soccer ball over the standard youth soccer ball. Of the 20 subjects, 65% of
them thought the Micro-Soccer ball was “easier” to kick. The “hardest” ball to kick was
the standard ball, chosen by 75% of the subjects. Ninety five percent of the subjects
thought the Micro-Soccer ball was “more fun” to kick than the standard youth soccer ball.

The specific results of the interview questions are provided in Table 23.

Table 23

Exit Interview Questions and Subject Selections

Micro Standard

Question ("big") ("small")
1. Which of the two balls did you like to kick best, the big one or small one? 19 '1

2. Which of the two balls was easier to kick. the big one or the small one? 13 7

3. Which of the two balls was harder to kick. the big one or the small one? 5 15

4. Which ball was more fun to kick, the big one or the small one? 19 1

 

1 l 4
Of interest to the investigator were the seven children who indicated the “small”

ball was easier to kick and the five children who indicated the “big” ball was harder to
kick. Listed in Table 24 is a summary of the stage levels and ages for the subjects who
thought the small ball (standard youth soccer ball) was easier to kick: one at stage one,
four years of age; two at stage two, three and four years of age; two at stage three, five

and eight years of age; and two at stage four, five and eight years of age.

Table 24

Stage Level and Age of Subjects Who Thought the
Standard Ball was Easier to Kick

Stage
1 2 .3. 4
Number of subjects 1 2 2 2
Age (years) 4 3 and 4 5 and 8 5 and 8

 

Summarized in Table 25 are the subjects who thought the big ball (Micro-Soccer
ball) was harder to kick: two at stage two, three and four years of age; two at stage three,
five and eight years of age; and one at stage four, four years of age. Since developmental
sequences are age related, but not age dependent, it may be possible that the children’s
perceptions followed a similar pattern. If that were true, the age related, not age
dependent relationship may explain the responses of the children who indicated the
“small” ball was easier to kick (even though it was heavier than the “big” ball) and the
children who indicated the “big” ball was harder to kick (even though it was 26% lighter

than the other ball). It is beyond the scope of this study, other than reporting the results

 

115
of the exit interview to draw conclusions about this interview. It is suggested that

consideration of equipment size may be of value in designing developmentally

appropriate equipment.

Table 25

Stage Level and Age of Subiects_ Who Thought the
Micro-Soccer Ball was Harder to Kick

 

 

Stage
.1. 2 § 5
Number of subjects * 2 2 1
Age (years) " 3 and 4 5 and 8 4

 

Summgg of results

This biomechanical study quantified angular displacements, velocities, and
accelerations of the developmental sequence of kicking in children three to eight years of
age at three specific points in the kick. These kinematic variables were compared to
predicted trends of the developmental sequence of kicking using a direct approach as
described by Haubenstricker, et al. (1981). Additionally, predicted trends were developed
for the angled approach.

Children identified as stages one through four completed trials using a direct
approach kicking a standard youth soccer ball and a newly developed light weight Micro-
Soccer ball. Children identified as stages three and four also completed trials using an

angled approach with both types of balls.

l 16
The first hypothesis tested was that the angular displacements, velocities and

accelerations would follow the predicted trends, for both approach types, as defined for
the preparatory, force production, and follow through phases. Most of the predicted
trends during the direct approach with both the standard youth and Micro-Soccer balls
were not supported in this study. The findings of this study related to the predicted trends
are listed below.

At maximum backswing the stage one performers exhibited a neutral hip position
at 180° when using the standard youth soccer ball. Stages two through four did not
exhibit hip hyperextension as predicted with either ball type.

In all kicking trials, the predicted trend that the more skilled subjects (stage four)
would exhibit a segmental relationship in which thigh rotation would dominate the force
production phase when compared to shank rotation, was exhibited in the current study.
Although, the segmental relationship described above, was observed in the stage three
and stage four subjects, the stage four subjects had greater magnitudes of differences
between the segmental rotations for the direct approach. The pattern observed in the
stage three subjects was not predicted, however it could be considered an elementary
form of the soccer paradox. The stage four subjects had a greater deceleration of the
thigh than did the stage three subjects which illustrated their increased skill level.
Contrary to the hypothesis tested, full knee extension at ball contact during a direct
approach to the ball was not found. Although, it was predicted that progressive knee
extension prior to and at ball contact would occur, the knee was flexed at ball contact in
all cases for all stages with both ball types. More research is required with larger sample

sizes, as well as high speed biomechanical video graphic analysis, to accurately assess the

1 17
differences between the work by Haubenstricker et al. (1981) and the current study, with

respect to knee angles at contact.

Knee extension continued during the follow through phase for all stages during
the direct approach for both balls tested, as predicted. Additionally, the stage four
subjects’ results supported the predicted trend of an airborne phase during the follow
through, as all of the stage four subjects were airborne, following contact during the
direct approach for both balls tested.

Many of the predicted characteristics of the angled approach were evident in the
current study. The predicted characteristic of the respective Basic and Mature Stage foot
placement was found in this study, as the Mature Stage performers placed the foot of the
support leg in the direction the ball was intended to be kicked, whereas the Basic Stage
performers placed their foot along the approach line. The placement of the support foot is
a characteristic that identified differences between skill levels during an angled approach.
The Basic Stage performers exhibited an increase in angular velocities of both the thigh
and the shank from maximum backswing to contact, which followed the predicted trend.

As in the direct approach, the soccer paradox, was found in the Basic and Mature
Stage subjects’ techniques. Additionally, the predicted trend of knee flexion at ball
contact was supported by these data during an angled approach to the ball. Finally, knee
flexion was maintained for the Basic Stage and Mature Stage subjects during the follow
through phase, for the angled approach with both soccer balls, as predicted.

Balanced design ANOVA (p < .10) analyses were conducted to determine: (1) if
differences existed in the rotations of the thigh, as well as the shank, of the kicking limb

between subjects exhibiting stages three and four while using a standard youth soccer ball

1 18
using a direct approach to the ball (hypothesis 2); (2) if differences existed in the

rotations of the thigh, as well as the shank of the kicking limb of the subjects using a
direct approach when compared with subjects using an angled approach, while kicking a
standard youth soccer ball (hypothesis 3); and (3) if the resultant ball velocity of the light
weight soccer ball will be greater than that of the standard youth soccer ball, regardless of
approach (hypothesis 4).

The second hypothesis tested for differences in the rotations of the thigh, as well
as the shank of the kicking limb between subjects exhibiting stages three and four while
using a standard youth soccer ball using a direct approach. Significant differences were
found at contact for both the angular velocity of the shank (p = .017), and angular
acceleration of the thigh (p = .003). Additionally, angular velocity of the shank (p = .024)
and angular velocity of the thigh (p = .026), were found significantly different at
maximum forward movement (follow through). Since this hypothesis, in its entirety, was
not shown significant, this hypothesis was rejected.

The third hypothesis of the current study tested if differences existed in the
rotations of the thigh, as well as the shank of the kicking limb of the subjects using a
direct approach when compared with subjects using an angled approach, while kicking a
standard youth soccer ball. This hypothesis was rejected. Significant differences were
found only for shank angular velocity at contact (p = .043). This hypothesis was
developed as a result of the work by Isokawa and Lees (1988), who determined that
kicking performance was significantly improved when using an angled approach of 45°.
A reason that may explain why the current hypothesis was rejected, was that the subjects

were inexperienced in performing the angled approach, and therefore, were unable to

1 19
capitalize on the greater range of motion provided by the angled approach with respect to

pelvic rotation, and inward rotation, adduction and flexion of the hip.

The final hypothesis of the current study tested whether or not the resultant ball
velocity of the light weight soccer ball would be greater than that of the standard youth
soccer ball, regardless of approach. A significant difference (p = .025) between the
standard youth soccer ball and the newly developed light weight soccer ball (Micro-
Soccer ball) was found. However, there was not a significant difference between the type
of approach used (p = .503 ), indicating that differences between the direct approach and
the angled approach did not exist with respect to ball velocity. As indicated previously,
the angled approach has been reported to increase kicking performance as measured by
resultant ball velocity following contact (Isokawa and Lees, 1988). The results of the
current study indicated that for this sample of subjects, the light weight ball had more of
an effect on ball velocity, than did the approach used. Again, inexperience by the
subjects using the angled approach may have been a factor in this finding.

The results of this study have identified specific kinematic variables of angular
displacements, velocities, and accelerations associated with the developmental sequence
of kicking in children, using direct and angled approaches to the ball. Insight into these
parameters has been gained for the developmental sequence of kicking. The lack of
significant differences between the kinematic variables between stages three and four, as
well as between the direct and angled approach types indicated: 1) that experience of the
subjects played a role; and 2) the two points of maximum backswing and maximum

forward movement may not discriminate within the skill of kicking.

120
Biomechanical study of the characteristics of kicking is an effective manner to

continue developing methods and techniques for teaching and coaching. The results of
the current study did find differences which may modify the findings of Seefeldt and
Haubenstricker (1972) and Haubenstricker, et al. (1981). Quantifying the kinematic
variables of angular displacements, velocities, and accelerations can supplement visual
assessment of the kicking skill. Finally, the effects of a light weight ball were evident for
this sample of children, regardless of the approach that was used, as the children were
able to kick the Micro-Soccer ball with a greater velocity than the standard youth size

three soccer ball.

Chapter 5

CONCLUSIONS AND RECOMMENDATIONS

Investigating the quantitative aspects of the development of kicking is important
to an increased understanding of kicking for the purposes of improving teaching and
coaching techniques and the skill development of children. Therefore, the purposes of
this study were: (a) to identify selected kinematic variables associated with children
exhibiting stages one through four while kicking a standard youth soccer ball and a newly
developed light weight soccer ball (Micro-Soccer ball) using direct and angled
approaches to the ball; (b) to identify the differences in selected kinematic variables
associated with children exhibiting kicking stages three and four using a direct and angled
approach to the ball while kicking a standard youth soccer ball; and (c) to determine if
there were differences in the resultant ball velocity of a standard youth soccer ball versus
a lightweight soccer ball, when kicked by subjects exhibiting stages three and four, for
both the direct and angled approaches.

The kinematic variables of angular displacements, velocities and accelerations for
the skill of kicking were determined for 20 children who ranged in age from three to eight
years of age. Subjects selected for participation in this study were classic examples of
one of the four developmental stages of kicking as outlined by Seefeldt and

Haubenstricker (1972). The children were assigned to developmental groups as follows:

121

122
two subjects each at stages one and two, and eight subjects each at stages three and four.

All of the subjects completed trials using the direct approach kicking a standard youth
soccer ball and the Micro-Soccer ball. The stage three and four subjects completed
additional trials using an angled approach kicking both ball types. Subject trials were
recorded using standard three-dimensional biomechanical videographic methods.
Subsequent calculations and smoothing of data were obtained from the Aerial
Performance Analysis System (APAS) modules for analysis.

Predicted trends were tested for each stage during the direct approach and Basic
and Mature Stages for the angled approach. The selected kinematic variables of angular
displacements, velocities, and accelerations were obtained at maximum backswing of the
kicking leg (preparatory phase), contact (contact portion of the force production phase),
and maximum height of the kicking foot after the ball left the foot (follow through
phase).

The first hypothesis, that the selected kinematic variables of angular
displacements, velocities, and accelerations would follow the predicted trends as stated
for the direct and angled approaches was rejected. Listed in Table 26 were the
characteristics found for the direct approach for both ball types. An overview of the
preparatory phase (maximum backswing), the force production phase (foot/ball contact),
and the follow through phase (maximum forward movement) is found in Table 26. The
changes in joint positions and kinematic variables listed in Table 26 were referenced from
the previous less skilled stage. Joint angles in the table are provided for use by the

practitioner when working with students or athletes.

Table 26

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Characteristics found for the Direct Approach with a Standard Youth/Micro-Soccer Ball

 

Stage 1

No hip hyperext.
1 80°/ 162°

No parallel thigh
Knee flexion 127°/ 131°
Hip flexion 155°/150°

Knee hyperextension
189°/flexion 177'

Stage 2 Stage 3
PREPARATORY PHASE
Step

Hip flexion 171°/ 174°
Knee flexion l61°/
extension 172'

<Hip flexion 177°/ 175°

>Knee flexion 135°/128°

FORCE PRODUCTION PHASE

Shank Angular Shank Angular

<9 / <9 <9 / <9

>u) / >(o >0) / >0)

>a / >0. >a / >a

Thigh Angular Thigh Angular

<9 / <9 >9 / >9

>0) / >0) >0) / «0

<a / xx «1 / <a

>Knee flexion 112°/ 108°
>Hip ext. 1620/1540

>Knee flexion 89°/95°
>Hipflexion 1540/1520
Elem. Soccer Paradox

FOLLOW THROUGH PHASE

Knee hyperextension
l 81°/1 86°

9 = Angular displacement
(o = Angular velocity
or = Angular acceleration

Knee flexion 175°/ 179°

Stage 4

Leap
>Hip flexion 174°/ 168°
>Knee ext. 142°/139°

Shank Angular

>9/>9
>(n/>co
>a/>a

Thigh Angular

>9/>9
<0.)/<(0
(Oi/<01

>Knee flexion 89°/95°
>Hip/1am 1500/1450
Soccer Paradox

Complete knee ext. 180°/
knee flexion 175'
Airborne

Bold = Difference between ball types
Italic = Additional findings

 

124
Predicted characteristics found during the preparatory phase of the direct approach

using a standard youth soccer ball and a Micro-Soccer ball are presented in Table 26.
Each of the stage four subjects used a leap on the final step of the approach. As
predicted, hip hyperextension was not found for the stage one subjects using either ball
type. Rather than hip hyperextension for stages two through four as predicted, slight hip
flexion was found at maximum backswing for both ball types, with the exception of stage
one subjects who exhibited a hip joint angle of 180° while kicking the standard ball.
Knee flexion was found at maximum backswing across all four stages with both ball
types, and (knee flexion) did not progressively increase as predicted.

At contact of the direct approach few of the predicted characteristics were found.
Mean shank angular velocity and acceleration were found to progressively increase from
stage one to stage four with both ball types. Also, mean thigh acceleration progressively
decreased across all four stages using the standard ball. As predicted, the stage four
subjects exhibited segmental rotations which were characterized as the soccer paradox.
The segmental rotations found in the stage four subjects coincided with the segmental
rotations discussed by Glassow and Mortimer (1968) and Putnam (1993). The mean
shank angular acceleration at contact was at 8355 deg/sec2 (7900 deg/secz, Micro-Soccer
ball) and the mean thigh angular acceleration was -6698 deg/sec2 (-8044 deg/secz, Micro-
Soccer ball), which indicated the presence of the soccer paradox for both ball types.
Although not predicted, the stage three subjects exhibited a similar pattern of the
rotations for the shank and thigh for both ball types, which was characterized as an
elementary form of the soccer paradox. The stage three subjects did not have as great a

difference in magnitude between the rotations of the shank and the thigh as the stage four

125
subjects. The greater difference in magnitude between the rotations of the thigh and

shank illustrated the stage four subjects’ higher skill level when compared to the stage
three subjects. An additional finding not predicted was that knee flexion at contact
progressively increased from stage one to stage four for both ball types. This finding of a
flexed knee at contact, is in sharp contrast with the descriptions of the developmental
sequence of kicking as discussed by Haubenstricker et al. (1981). Knee flexion at contact
is a characteristic that is taught by many soccer coaches and is taught to coaches at
coaching academies. Finally, hip flexion was found at contact for all four stages with
both ball types.

During the follow through of the direct approach, as predicted, all of the stage
four subjects were airborne. Although being airborne is not the only criterion for a stage
four subject, it did indicate that the stage four subjects produced sufficient momentum
during the kick in order to become airborne. Production of sufficient momentum during
the kick, resulting in the body becoming airborne is a characteristic that illustrated greater
skill level in a performer.

Few differences were found when comparisons were made between the standard
youth soccer ball and the Micro-Soccer ball using a direct approach with respect to the
predicted characteristics. The Micro-Soccer ball was not found to have an effect on the
angular displacements, velocities, and accelerations as previously predicted. During the
preparatory phase, the stage one subjects exhibited a greater backswing with the standard
ball than with the Micro-Soccer ball, indicated by a hip joint angle difference of 18°.
Additionally, during the preparatory phase, the stage two subjects’ knee flexion while

kicking the standard soccer ball was 11° less than the knee joint angle while kicking the

l 26
Micro-Soccer ball. At contact, a decrease was found in thigh angular velocity for the

stage three subjects with the Micro-Soccer ball, whereas an increase was found with the
standard ball. Also at contact, mean thigh angular deceleration was not as great while
subjects kicked the Micro-Soccer ball compared with the deceleration while kicking the
standard ball. During the follow through, minimal differences were exhibited in the knee
and hip joint angles.

Research is prevalent using adult subjects in the study of kicking. However, to
date no literature was found on the developmental sequence of an angled approach to the
ball in children. Subjects identified at stages three and four were used in this study to
evaluate the predicted trends of the angled approach. Predicted trends were established
for the Basic Stage (stage three) and the Mature Stage (stage four) using both the standard
youth soccer ball and the newly developed Micro-Soccer ball.

A number of the predicted trends for the angled approach using a standard youth
soccer ball and Micro-Soccer ball were supported (Table 27). During the preparatory
phase with both ball types, the Basic Stage performers placed their non-kicking support
foot along the angled approach line, in contrast with the Mature Stage performer’s foot
placement which was along the intended path the ball was to be kicked. The Mature
Stage subjects’ support foot placement reinforced the thought by the current study’s
investigator, that a more mature kicking technique was required to perform an angled

approach at a high level of skill.

127
Table 27

Characteristics Found for an Angled Approach Using a Standard Youth/Micro-Soccer Ball

 

Basic Stage Mature Stage
PREPARATORY PHASE
Step Leap
Support foot along approach path Support foot parallel to intended
direction of ball travel

Hip flexion l75°/l72° >Hip flexion 169°/ 171°
Knee flexion 135°/130° >Knee extension l44°/141°

FORCE PRODUCTION PHASE
Increasing thigh and shank velocity Soccer paradox
Hip flexion 153°/150° >Hr’pflexion [500/>extension I520
Knee flexion lOO°/94° >Knee flexion 97°/>extension [000
Elementary Soccer Paradox

FOLLOW THROUGH PHASE

Knee flexion 177°/ 175° >Knee flexion 176°/176°
Hip flexion l38°ll38° >Hip flexion 128°/128°

Italic = Additional findings

 

The Mature Stage performers’ technique enabled them to use the additional
actions of inward rotation and adduction of the support leg hip as a result of the
positioning of the non-kicking leg. This not only increased the number of muscle groups
involved, but also increased the range of motion through which the leg moved, thereby
enabling the segments to reach higher velocities prior to ball contact. Also as predicted,
knee flexion at maximum backswing (preparatory phase) was found to be greater for the
Mature Stage subjects than for the Basic Stage subjects (Table 27). The greater knee

flexion exhibited by the Mature Stage subjects resulted in a shortened moment arm,

 

128
allowing the subjects to swing the leg through quickly, reaching greater kicking limb

velocities.

At contact with the standard ball, mean knee joint angles were found to be 100°
for the Basic Stage and 97° for the Mature Stage subjects with the standard ball. With the
Micro-Soccer ball, the Basic Stage subjects exhibited a 94° knee joint angle, while the
Mature Stage subjects exhibited a 100° knee joint angle at contact. Although the knee
was in a more extended position for the Mature Stage subjects in comparison to the Basic
Stage subjects, the knee was still in a flexed position. These findings supported the
predicted characteristics of knee flexion at contact. Additionally for both ball types, hip
flexion was found in the Basic Stage subjects as predicted, with greater hip flexion found
for the Mature Stage performers. As predicted for the Basic Stage performers, shank and
thigh angular velocities were found to have increased from maximum backswing to
contact for both ball types.

As found in the direct approach (stage four), the soccer paradox relationship was
found for the Mature Stage subjects during the angled approach with both ball types. The
relative angular accelerations found in the Mature Stage subjects’ thigh and shank
highlighted the difference between the Basic and Mature Stage subjects with respect to
coordination and technique used during an angled approach.

During the follow through phase of the angled approach, knee flexion was
predicted to be maintained as hip flexion occurred for both the Basic and Mature Stage
subjects. Knee flexion was found to be maintained at maximum forward movement of
the kicking foot for the Basic Stage subjects and for the Mature Stage subjects with

minimal differences between ball types (Table 27). Hip flexion was also found in the

129
follow through phase, with the Mature Stage subjects’ hip flexion greater than the Basic

Stage subjects, with no difference between ball types. The difference in hip flexion
between the two stages was explained as a result of increased segmental velocities by the
Mature Stage subjects. The increased segmental velocities resulted in increased
momentum of the leg segments, thereby causing increased hip flexion during the follow
through. The greater momentum was substantiated by the resultant ball velocity at
contact.

Most of the predicted trends were found for the angled approach using both the
standard youth soccer ball and the Micro-Soccer ball, with minimal differences between
ball types. A finding not predicted, that was found for both approaches and both ball
types was that of an elementary form of the soccer paradox in the stage three subjects.
The magnitude of differences of the rotations of the thigh and shank were not as great for
the Basic Stage (stage three) subjects as for the Mature Stage (stage four) subjects.
However, as skill level increased across stages, there was a greater deceleration of the
thigh, relative to the acceleration of the shank at contact. The rotations of the thigh
relative to the shank appear to be characteristic differences between skill levels.
Although, a coach or a teacher should not teach a performer to stop the thigh purposely,
as a performer’s skill level increased it should be possible to visually observe what
appears to be a slowing or a stopping of the thigh as the shank moves to contact. The
information on the movement of the thigh and the shank should help the practitioner in
evaluating levels of kicking skill.

The second hypothesis tested, which investigated significant differences in the

rotations of the thigh, as well as the shank, of the kicking limb between subjects

130
exhibiting stages three and four while using a standard youth soccer ball was rejected in

this study. Although rejected as a whole, several differences were found significant at
contact and maximum forward movement. The lack of measurable significance at
maximum backswing for this study may be explained by the point chosen for analysis. If
the point selected were truly maximum backswing, the movement of the kicking leg
would have stopped or there would be minimal movement prior to beginning its forward
swing, regardless of the stage.

Significant differences for the stage three and four subjects in angular velocity of
the shank (p = .017) and the angular acceleration of the thigh (p = .003) were found at
contact. The stage four subjects were found to have a greater shank angular velocity and
a greater thigh deceleration. The significant differences found in the angular velocity of
the shank as well as the angular acceleration of the thigh may have indicated that the
stage four subjects were better able to utilize the segmental relationships in performing
the kick. Also, the stage four subjects’ shank angular velocity may have been
significantly greater because they were able to capitalize on the movement of the thigh.

At maximum forward movement of the kicking foot, a significant difference was
found for the angular velocity of the shank (p = .024) and the angular acceleration of the
thigh (p = .026). The significant differences found in the angular velocity of the shank
and the angular acceleration of the thigh may have been a result of a reduction in the
relative moment arm of the kicking leg for the stage four subjects while airborne.
Modification of the relative moment arm length would be required for the purpose of
balance and timing. Examining the moment arm length relative to balance of the body

was outside the scope of the current study.

131
Even though the second hypothesis was rejected as stated, observable differences

also were found in the graphs of angular velocity of the thigh and shank for randomly
selected stage three and four subjects. It appeared that there was a difference in the
timing and coordination of the leg segments between the stage three and four subjects
with respect to angular velocities of the thigh and shank. Although a coach or teacher
may attempt to encourage a participant to maximize velocity of the kicking limb
segments, timing and coordination of the kicking sequence must be emphasized for
children regardless of the stage level to develop correct kicking technique.

The third hypothesis of this study stated that there would be significant
differences in the rotations of the thigh, as well as the shank, between a direct approach
and an angled approach using a standard youth soccer ball. This hypothesis was rejected.
As discussed earlier, the angled approach has been attributed to increased kicking
performance by adults. The only significant difference found was that of the angular
acceleration of the shank at contact (p = .043). The significant difference between the
approaches with respect to the angular acceleration of the shank was likely due to the
increased difficulty of the angled approach over the direct approach and the inexperience
of the subjects performing this task. Overall, the angular acceleration of the shank was
lower for the angled approach when compared to the direct approach. A lack of
experience with an angled approach may have caused the children to concentrate more on
the task of completing the approach, rather than executing a maximal effort kick. The
foot placement of the stage four subjects indicated that other variables, such as timing and
technique, could contribute to performance of the angled approach (Mclean & Tumilty,

1993). Finally, all the changes in movement which occur during the kick may not have

132
been captured by the video tape due to the relatively low fiarne rate of the cameras.

Intricate changes in human movement are difficult, if not impossible, to capture without
high frame rates.

The final hypothesis of this study stated that the resultant velocity of the
lightweight ball (Micro-Soccer ball) would be greater than that of the standard youth
soccer ball regardless of the approach. For both approaches, resultant ball velocities were
significantly different between the Micro-Soccer ball and the standard youth size three
soccer ball (p = .025). The mean initial velocities (V o) of the standard ball during the
direct approach were 7.46 m/sec and 11.66 m/sec for stages three and four, respectively.
In comparison, the mean initial velocities of the Micro-Soccer ball using the direct
approach were 9.03 m/sec and 14.24 m/sec for stages three and four, respectively. The
mean initial velocities of the standard ball during the angled approach were 8.26 m/sec
for the Basic Stage and 10.45 rn/sec for the Mature Stage. Finally, the initial velocities
for the Micro-Soccer ball using an angled approach were found to be 8.90 m/sec for the
Basic Stage and 12.62 m/sec for the Mature Stage. The lightweight ball did have an
effect on ball velocity, with the Micro-Soccer ball having a greater resultant velocity than
the standard youth soccer ball for both approaches. However, the lightweight Micro-
Soccer ball was not shown to be a significant factor in ball velocity between the direct
and angled approaches in the current study (p. = .503). It is likely that a lack of
experience of the children completing an angled approach, caused the children to
concentrate more on the task of completing the approach which may have resulted in a

less than maximum ball velocity for the angled approach.

133
Not only did the subjects kick the Micro-Soccer ball with greater velocity, they

appeared to enjoy kicking the ball more. Through an exit interview, 95% of the subjects
liked to kick the Micro-Soccer ball the best, 65% thought it was easier to kick, 75%
thought the standard youth ball was harder to kick, and 95% thought the Micro-Soccer
ball was more firn to kick. The Micro-Soccer ball was slightly larger in circumference
than the standard youth ball, and 26% lighter.

Several issues arose as a result of the limited number of the predicted trends being
supported as well as in the findings of the lack of significance in the hypotheses of this
study. The hyperextended position of the hip at maximum backswing, defined by some
researchers, may be due to one of or both of the following: 1) a misperception of the
trunk position relative to the thigh, and 2) lumbar hyperextension. If the trunk were
inclined anteriorly at maximum backswing of the kicking leg, hip hyperextension may
appear to be present. However, if the inclination of the trunk is examined relative to the
thigh, hip hyperextension may not exist. Additionally, if the pelvis rotates anteriorly, hip
hyperextension may also be perceived by the observer. Relative to the pelvis however,
no hip hyperextension exists. These misperceptions may result in inaccurate visual
assessments of hip positions relative to the trunk. Although this study did not address
trunk inclination angle, differences between the stages with respect to trunk inclination at
maximum backswing, contact, and maximum forward movement were observed on the
video tapes of the subjects.

Another issue was that of the selection of the specific points at maximum
backswing and maximum forward movement. The selection of these specific points may

have resulted in a lack of significant differences because of the limited movement of the

134
segments at these points in time. The potential of missing real differences may have

occurred as a result of the video film speed and the data reduction process. It may have
been more appropriate to select numerous points along the path of the kick in order to
represent the full sequence to determine if significant differences existed. However, these
points were selected based on the work by Haubenstricker et al. (1981)

Additionally, the qualitative characteristics developed by Seefeldt and
Haubenstricker (1972) and subsequently validated by Haubenstricker et al. (1981)
distinguished points along a continuum of kicking. Other variables, such as balance or
interactions of other body segments may have contributed to the identification of kicking
skill level and subsequent significant differences.

The results of the current study will add to the foundation of the developmental
sequence of kicking using the direct approach. The current study also laid a foundation
with respect to the developmental sequence of kicking using an angled approach.
Additionally, it has been shown that a lightweight ball can improve kicking performance,
as measured by resultant ball velocity. Finally, coaches and teachers will be able to use

this information to improve kicking skill in children.

Recommendations

1. Future studies should consider studying subjects beyond the three to eight year old
range of the current study. Samples of subjects of different ages would provide greater
input into the development of kicking. Additionally, comparisons between “mature”

level stage four children could be compared to “elite” soccer players, such as those in the

135
Olympic Development Program, or on select travel teams. Even though the magnitudes

of the selected kinematic variables would be markedly different, the patterns observed
could be compared.

2. Future studies should consider the use of only soccer experienced children, non-
soccer experienced children, or a comparison of the two classifications to examine the
development of kicking in children.

3. Future studies should consider longitudinal studies of children to examine
developmental changes.

4. Future studies should consider the interactions of the thigh, shank and foot. Studying
the interaction between these segments would enable the investigator to determine the
contributions of the selected segments. Skill level comparisons could be conducted to
differentiate between skill levels.

5. Future studies should consider the development of a targeting solution of the pelvis
and trunk to determine their relative positions during a kick. This would further aid in the
accurate description of a kick.

6. Kinetic variables should be considered. Force platform data would add to the current
study’s examination of the development of kicking in children. For example, ground
reaction forces could be compared between skill levels to further differentiate between
skill levels.

7. Future studies should consider the use of high speed cameras to study the
development of kicking. High speed cameras, integrated with automated motion analysis
systems would enable the researcher to identify variables, otherwise unobservable, as a

result of inadequate camera speed. Because of the ballistic nature of the skill of kicking,

136
an increased number of data points could be collected with high speed cameras in order to

more intricately analyze the skill of kicking.

8. Future studies should consider the use of automated motion analysis systems in order
to video tape an increased number of subjects and increase the number of identified
landmarks. The investigator would be able to increase statistical power by increasing the
sample size, as well as identify patterns of motion of other body segments.

9. Future studies should investigate the scaling of equipment to children. Different
weights and sizes of soccer balls are known to affect kicking performance as measured by

resultant ball velocity.

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APPENDIX A

APPENDIX A

WRITTEN INFORMED CONSENT
FOR

A kinematic analysis of the developmental seguence of kicking using a direct and angled

approach *
Michigan State University

Department of Physical Education and Exercise Science

1. I have freely consented to take part in a scientific study investigating the
kinematic variables associated with the developmental sequence of kicking by Alfred H.
Bransdorfer under the direction of Dr. Dianne Ulibani.

2. I understand that to perform this analysis the following measurements will be
taken:
a. I will be video taped as I kick two balls, each three (3) times using
a direct and angled approach to the ball (12 kicks plus 2 extra for
miss kicks). Note: Stage one and two subjects will use only a
direct approach and complete six kicks.

b. I will be involved in one filming session lasting approximately 45
minutes. ‘

c. I will have small reflective balls attached with double sided hypo-
allergenic tape to my shoe, ankle, knee, shin, and hip to aid in
determination of those locations during the analysis phase of the

study.
d. I will have the lengths and heights of specific limbs measured as
well as my body weight.
3. I understand that if I am injured as a result of my participation in this research

project, Michigan State University will provide emergency medical care if necessary. I
further understand that if the injury is not caused by the negligence of MSU I am
personally responsible for the expense of this emergency care and any other medical
expenses incurred as a result of this injury.

4. I understand that I am free to discontinue my participation in the study at any time
without penalty and will in no manner effect my future relationship with Michigan State
University.

5. I understand that the participation in this study is strictly voluntary and will not
involve payment.

6. I understand that data from my performances may be used for demonstrations,
instruction, and study.

7. I understand that my name will not be used in any publication, presentation, or
discussion of data based upon my performances.

141

 

142

8. I understand that the video taped recording of my trials, that could identify me
will not be used in any publication, presentation or discussion without my expressed
written consent.

9. I understand I will receive a copy of my individual results, and that I can receive

additional information about this study or these results after my participation is
completed.

Date:

Parent/Guardian Signature

 

Minor Assent( ) Yes ( ) No
Address

 

 

 

Phone Number

 

 

APPENDIX B

 

APPENDIX B

SUBJECT INFORMATION AND ANT HROPOMETRY

A KINEMATIC ANALYSIS OF THE DEVELOPMENTAL SEQUENCE OF KICKING
USING A DIRECT AND ANGLED APPROACH

Date

 

Name

 

Address

 

City State

 

Zip

 

Phone Number ( 1
Date of Birth

 

Measurements

Height Weight

 

Right Leg

Thigh (Greater trochanter of femur to lateral epicondyle)
Shank (Lateral condyle of tibia to lateral malleolus)
Foot (Lateral malleolus to distal end of 5th metatarsal)
Leg height (Greater trochanter to floor)

Shank height with foot (Lateral condyle of tibia to floor)

Notes:

143

Subject #

 

APPENDIX C

APPENDIX C

EXIT INTERVIEW
FOR
A KINEMATIC ANALYSIS OF THE DEVELOPMENTAL SEQUENCE OF KICKING
USING A DIRECT AND INDIRECT APPROACH

Subject #

 

Directions: Please read each question to the subject and circle their response. The
subject's parents may need to help assist the child in answering.

1. Which of the two balls did you like to kick best, the big one or small one?

2. Which of the two balls was easier to kick, the big one or the small one?

3. Which of the two balls was harder to kick, the big one or the small one?

4. Which ball was more fun to kick, the big one or the small one?

144

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