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This is to certify that the

thesisentitled
A BIOMECHANICAL COMPARISON OF FORWARD AND REARWARD
HUMAN PROPULSION

presented by

Timothy William Flynn

has been accepted towards fulfillment
of the requirements for

Master of Science degree in Biomechanics

 

@Sfimréjgéfifia

R. W. Soutas-Little Ph.D.

 

Major professor

Date April 23, 1990

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

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University

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iii—Ti

MSU Is An Affirmative ActiorVEquai Opportunity Institution

 

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A...

A.BIOMICHANICAL COMPARISON OF FORHARD AND REARNARD
HUMAN PROPULSION

by
Timothy William Flynn

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Biomechanics

1990

7‘

(04—5-— 7/

answer
a BIOMECHANICAL commsou or FORWARD mm mm am
pmpmrou
by

Timothy William Flynn

The purpose of this thesis was to investigate the
stance phase of rearward walking and running and compare
these to their forward ambulation counterparts. The
saggital plane of the right knee was analyzed. The knee
muscle moment, power, and work requirements were determined.
EMG signals were captured from six muscles. The ground
reaction torque was analyzed. Statistically greater peak
negative power and negative work occurred during forward
walking and forward running. Significantly different
patterns of EMG activity were found between forward and
rearward conditions. The ground reaction torque suggested a
decrease in the tibial internal rotation and subtalar
pronation during rearward walking and rearward running
respectively. The use of retropropulsion in the

rehabilitation of overuse injuries of the knee is discussed.

ACKNOWLEDGEMENTS

The author wishes to express his appreciation to the
following people for making the completion of his Master of
Science degree possible:

To my major professor Dr. Robert Soutas-Little for
encouraging me to "take it a step further."

To Dr. Roger Haut and Dr. Allen Jacobs for serving on
my committee.

To Robert Wells for his "superb" programming ability.

To LTC(P) David Greathouse, my mentor and friend, for
his encouragement and confidence in my abilities.

To my mother, for her constant love and encouragement.

To Susan, David, and Phillip, for the happiness which
you bring me and the patience you show for a wandering mind.

And finally, to my father, John Patrick Flynn for

continuing to journey with me daily, "Dad, your presence is
felt."

iii

TABLE OF CONTENTS

LIST OF TABLES . .
LIST OF FIGURES
Chapters
I. INTRODUCTION . . .
II. SURVEY OF LITERATURE
Retropropulsion .
Muscle Power and Work
Electromyography
Functional and Clinical
III. EXPERIMENTAL METHODS .
Equipment . . . . .
Subjects . . .
Data Collection .
IV. ANALYTICAL METHODS
V. RESULTS AND DISCUSSION

Walking . . . . . .
Running

VI. CLINICAL IMPLICATIONS
VII. CONCLUSIONS

BIBLIOGRAPHY

iv

Biomechanics.

Page

vi

101
106
108

Table

\OQQQU‘IAMNH

t4 H H
N F' c:
O O 0

LIST OF TABLES

Individual subject traits . . . . . . .

Target number and anatomical location

Average peak positive power - walking.

Average peak negative power - walking .

Average positive work - walking . . . .

Average negative work — walking . . . .

Total on time for individual muscles - walking.
Average peak positive power - running .
Average peak negative power - running .

Average positive work - running . . . .

Average negative work - running .

Total on time for individual muscles - running.

Page
18
22
58
59
59
60
62
92
93
93
94
96

LIST OF FIGURES

Figure Page
1. Calibration space . . . . . . . . . . . . . . . 16
2. Sun 4 workstation . . . . . . . . . . . . . . . 19
3. Force plate and laboratory coordinate systems . 19
4. Neuromuscular stimulation of motor points . . . 21
5. Target locations on subject . . . . . . . . . . 23
6. Reproducibility of z - force data . . . . . . . 25
7. Program output calc_twf . . . . . . . . . . . 30
8. Forward walking knee muscle moment curves . . . 32
9. Rearward walking knee muscle moment curves . . 39

10. Forward walking power curves . . . . . . . . . 45

11. Rearward walking power curves . . . . . . . . . 52

12. Forward walking EMG pattern . . . . . . . . . 61

13. Rearward walking EMG pattern . . . . . . . . . 61

14. Ground reaction torque forward vs rearward

walking . . . . . . . . . . . . . . . . . . . . 65

15. Forward running knee muscle moment curves . . . 67

16. Rearward running knee muscle moment curves . . 73

17. Forward running muscle power curves . . . . . 80

18. Rearward running muscle power curves . . . . . 86

19. Forward running EMG pattern . . . . . . . . . . 95

20. Rearward running EMG pattern . . . . . . . . . 95

21. Ground reaction torque forward vs rearward
running . . . . . . . . . . . . . . . . . . . 99

vi

I. INTRODUCTION

During the last three decades there has been a steadily
increasing emphasis on maintaining a healthy lifestyle. In
an effort to increase the quality of one's life and decrease
the risk of disease, the public has become more interested
in aerobic fitness. Running is one of the most efficient
means of increasing cardiovascular endurance. In this
country alone, millions of people are running everyday.
Unfortunately, a large percentage of runners and
recreational joggers develop debilitating knee pain during
their training. James and associates(24) found the knee
joint to be the most common cause of pain in runners and the
patellofemoral joint to be the most common area of
dysfunction. One factor contributing to this is the large
forces that enter the body during running. A large amount
of muscle energy is expended in an attempt to deccelerate
the body. The knee joint demonstrates this via the large
eccentric activity of the quadriceps group during the
initial stance phase of running. The early stance to mid
stance phase of running is considered the time where
biomechanical loads give rise to knee dysfunction.

Despite the common occurence of overuse injuries around

the knee, there is no common successful prevention method or

2
rehabilitation protocol. One method that is gaining

popularity in the rehabilitation community in the treatment
of these injuries is backward or retro walking and running.
Despite the fact that retropropulsion is becoming a common
modality in the rehabilitative process, little research
exists that analyzes the unique biomechanics of this
activity.

The purpose of this research was to investigate the
stance phase of retro walking and running and to compare
this to their forward ambulation counterparts. The knee
will be the primary joint of interest. The model of
investigation will center on the determination of the knee
muscle power and work. Kinematic and kinetic data will be
captured. Electromyography of six muscles surrounding the
knee will give insight to the primary muscle firing pattern
during these activities. The functional and clinical
significance of retropropulsion will be addressed throughout

this thesis.

II. SURVEY OF LITERATURE

The survey of literature will be divided into four
sections: retropropulsion, muscle power, electromyography,
and clinical & functional biomechanics.

Retropropulsion

Backward walking and running as a form of movement has
probably been utilized since man began upright activity.
Various daily activities require us to move backwards to
position our upper extremities. Numerous sporting
activities require backward running. Just as the cromagnum
man back-pedaled in self-defense of a wild animal, the
modern day athlete runs backward to position himself on the
defensive field. Though normal children develop the ability
to move backward at an early age, it appears that it
requires a high central neural program to perform.
Thorstensson's(43) study of five subjects performing
backward and forward walking noted that the lower limb
followed essentially the same trajectory when performing
forward and backward walking. However, these trajectories
are in opposite directions, in order to accomplish this
dramatic and very specific change most muscles changed their
pattern of activity in relation to the different movement
phases. Providing that the same neural circuitry is

utilized in forward and backward walking, Thorstensson

3

4
suggested a marked and specific modifiability occurred in

the neural network that generates locomotion.

In 1980, a short article by Flodberg(19) reported the
rehabilitation value of retro running in the treatment of an
overuse injury of the hip. Mackie et al.(29) investigated
the effects of a three month backward training program in
twenty one subjects following ACL injury. They reported a
significant increase in hamstring and quadriceps power, as
measured on a CYBEX II testing apparatus. Bobath(8) and
Brunnstrom(10) recommend backward movement in the evaluation
and treatment of motor control in hemiplegic patients.

Several authors have studied the kinematic differences
in forward and backward ambulation. Bates et al.(7) studied
nine female runners in forward and backward conditions. The
authors assumed running backwards to be kinematically
opposite of forward running. Bates et al. reported backward
running required significantly less hip joint range of
motion and greater knee joint range of motion. The authors'
theorized that muscle function would reverse from concentric
to eccentric action and vice versa. Bates and McCaw(6)
tested two subjects walking forward and backward on a
treadmill. The greatest differences were noted at the knee
joint. In forward walking, the knee joint exhibited the
well documented three periods of load accepting flexion,
followed by the extension period of mid stance, and a second

flexion period prior to toe off. Backward walking consisted

5
only of a single extensor phase throughout the entire

support period.

Shuck(41) agreed with the finding of a single extensor
period in backward walking. The author noted that the ankle
dorsiflexes sharply after initial toe strike in backward
walking, apparently compensating for the lack of the knee
flexion phase normally seen in forward walking. The knee
appears to be the primary shock absorber in forward walking
and running and the ankle in backward walking and running.

Vilensky et al.(47) studied sixteen parameters in four
subjects walking forward and backward on a motor driven
treadmill. In contrast to Grillner's prediction(20), that
human backward walking is achieved by a simple change in
phase relationship between the hip and knee joints, Vilensky
et al. noted marked changes in the movements of the hip and
knee joints and their interactions. The authors were in
agreement with Bates and McCaw's(6) finding of a single
extensor support phase at the knee during backward walking.
Vilensky et al. also noted that backward walking was
achieved by a faster cadence, but a decreased stride length
when compared to forward walking at the same speed. A
decrease in stride length tends to be a protective strategy
for gait disturbances(12) such as paresis, pain, and
coordination disorders(27). Given the fact that this
protective strategy occurs in healthy individuals when
stability is challenged, Vilensky et a1.(47) proposed that

backward walking "threatened" stability.

6
Ground reaction forces have been measured in backward

running. Armstrong et al.(2) briefly described vertical,
fore-aft, and medial-lateral force differences during
forward and backward running in eight subjects. The lack of
a defined first peak in backward running vertical force was
noted. Armstrong et al. interpreted this as a more gradual
dissipation of force controlled by the eccentric calf muscle
contraction. The peak lateral force was greater and lasted
for a larger amount of the support time in backward running,
when compared to forward running. The investigators'
interpreted this as necessary to maintain stablility while
running backwards.

Threlkeld et a1.(45), in a study of ten runners,
concluded that backward running produced lower vertical'
impulse stress than forward running. The investigators'
also noted that an eight week training program of backward
running improved concentric knee extensor torque at low
speeds on a isokinetic dynamometer. Threlkeld et al.
reported backward running could be clinically useful for
reducing stress to injured joints and for increasing knee
extensor strength.

Kramer and Reid(25) studied one subject walking forward
and backward using high speed cinematography and surface
electromyography. The authors noted that the lower
extremity muscles were electrically active for greater
sustained periods of time (consistent activity), and also

demonstrated a greater degree of inconsistent electrical

7
activity during backwards walking than during forward

walking. Muscles were more active in a pulling and
stabilizing function during backward walking than during

forward walking.

Muscle power and work

In order to gain insight into the rehabilitative and
training siginificance of backward ambulation, a
biomechanical evaluation must assess muscular activity.
Winter(54) states that only by examining the mechanical
powers at each joint can an assesment of the importance of
the muscles at the ankle, knee, and hip be ascertained.

In Elftman's classic studies(14,15), he outlined
methods for calculating the rate of work done on the leg and
further demonstrated this by analyzing one stride of one
runner(16). Quanbury and colleagues(37) studied the power
flow to the lower extremities during the swing phase of
walking.

Robertson and Winter(39) studied two subjects during
the complete walking cycle. The authors studied the rate of
work done by the muscle moments and termed this muscle
power. Where muscle power is the resultant joint muscle
moment vector multiplied as a dot (scalar) product with the
joint angular velocity. When the resultant joint moment is
in the same direction as the joint angular velocity
concentric muscle action occurs, if the directions are

opposite an eccentric muscle action is occurring. With this

8
model the lower extremity muscles could be viewed as

generating mechanical energy or absorbing mechanical energy
via concentric or eccentric muscle contraction respectively.
Robertson and Winter(39) concluded that the measurements of
joint and muscle power were valid throughout the walking
cycle for all trials of the three leg segments studied,
except the ankle during weight acceptance and late push off.
The authors also noted that the assumption of the joints
acting as an ideal hinge connection was valid for joint
moment and muscle power analysis.

Winter(54) studied the moments of force and mechanical
power in eleven subjects performing slow jogging trials. He
described five distinct phases of the knee muscle power
pattern: an initial shock absorbing peak during weight
acceptance, a small generation burst during early push off,
a major absorption pattern during late push off, a third
absorption peak decelerating the leg and foot prior to
impact, and a final small positive burst as the knee flexors
rotate the leg posteriorly to reduce forward velocity prior
to heel contact. Winter also found that over the entire
stride the knee muscles absorbed 3.6 times as much energy as
they generated, and the ankle muscles generated 2.9 times as
much as they absorbed.

Ae and associates(l) studied five skilled sprinters at
increasing running speeds. The authors found that the

muscle power patterns were consistent for increasing speed,

9
but that the magnitude of muscle power increased as running

speed increased.
llectromyography

Elliot and Blanksby(l7) stated by synchronizing
electromyography (EMG) with cinematography one can gain a
more complete understanding of the integrative pattern of
electrophysiological and mechanical parameters in the
performance of human locomotor skills.

Numerous investigators have studied EMG activity of the
lower extremity musculature during walking. In 1963 Moore
and colleagues(32) studied muscle activity in walking with a
system which telemetered the EMG signal. This allowed the
subject to be freed from a cumbersome umbilical cord which
followed the subject through his or her activity. Since
that time multichannel telemetry systems have advanced
considerably and now allow for maximum freedom of movement
and essentially no added weight for the subject.

Yang and Winter(56), studying eleven subjects walking
at three different cadences, noted a significant change in
the magnitude of the signal at increasing velocity but the
shape of the EMG pattern generally remained similiar at the
different cadences. Yang and Winter noted that although the
EMG pattern changes across subjects revealed a seemingly
systematic trend, the individual subject responses varied
greatly. The investigators thought that these individual
differences could be related to the trade off in function

between synergestic muscles, the differences in fiber type,

10
or the kinetic differences in each of the subjects walking

gait.

Arsenault et al.(3) attempted to validate the notion of
a normal profile of BMG signals during gait. Within a
subject all the data obtained from a given muscle were
observed to be extremely stable. This indicates that gait
might be programmed, if programming is defined as high
repeatibilty in neuromuscular output. However, analysis
across subjects, demostrated differences between the
muscular recruitment profile of several of the muscles
investigated. The authors felt these peculiarities for a
particular muscle for individual subjects were important,
since biologically speaking such peculiarities in the EMG
firing pattern would contribute to the production of an
overall joint moment history differing from one subject to
another.

Arsenault et al.(4) accumulated EMG data over 10
strides in eight subjects. The author concluded that since
intra-subject variations were usually small, three strides
per subject would offer very reliable EMG data for that
subject. Furthermore, the investigators reported three
strides per subject to be reliable for inter-subject
comparisons.

The EMG pattern has also been studied in running.
Elliot and Blanksby(l7), studying ten females running on a
treadmill, noted that from foot contact to mid stance the

lower extremity muscle activity was concerned primarily with

11
stabilization. Lower limb stabilization then gave way to a

powerful driving thrust during the mid and late support
phases. Similar results were reported by Elliot and
Blanskby(18), when analyzing ten male runners.

At foot strike during running, marked activity has been
shown in the vastus lateralis and vastus medialis in
preparation for the rapid loading which subsequently
occurs.(52) This correlates with Komi(26) who reported that
muscle activity during the eccentric phase of contact was
much greater in magnitude in all muscles than during the
concentric phase.

Functional and clinical biomechanics

Mechanics of the foot/ankle complex significantly
influences patellofemoral joint mechanics. A brief
description of the closed kinetic chain motion of the
subtalar joint, and its influence on the knee is now
presented.

Root and colleagues(40) describe pronation of the
subtalar joint during weight bearing consists of calcaneal
eversion with the talus adducting and plantar flexing.
Supination is described as calcaneal inversion with
abduction and dorsiflexion of the talus. Inman(22) states
that the primary function of the subtalar joint is to absorb
transverse plane rotation of the lower extremity. Levens
and colleagues(28) classic study on transverse rotation of
the lower extremity in walking found tibial transverse

rotations averaging 19 degrees. The researchers also

12
reported relative transverse rotation of the tibia with

respect to the femur to average 9 degrees.

During the initial stance phase of gait the
weightbearing limb is internally rotating. To allow the
foot to stay in the line of progression, the subtalar joint
absorbs the internal rotation of the lower extremity by
pronating.(22,40) James(23) reports pronation reached a
maximum at 15% of the stance phase of walking and at 40% of
the stance phase during running. After maximum pronation is
reached the subtalar joint gradually supinates. James and
colleagues(24) state that excessive or prolonged pronation
during the support phase creates increased forces not only
applied to the supporting structures of the foot but also to
the knee. Furthermore, when tibial internal rotation is
increased and prolonged with excessive pronation, more
transverse rotation must be absorbed in the knee joint with
subsequent disturbance of the normal tibia-femoral
rotational relationship and alteration in patellofemoral
mechanics.-

Tiberio<46) states that five extra degrees of pronation
occurring during midstance holds more potential for
producing pain than five extra degrees occurring during the
initial contact phase. He further states that since the
subtalar joint should begin supinating during midstance, the
extra pronation at this time is actually a much greater
functional deviation and will require greater compensation

on the part of the femur.

13
A number of authors have reported a reduction in

patellofemoral symptoms by controlling the amount of
pronation during the stance phase of running(ll,12,34).
Foot orthotics and specific shoe design are methods used to
decrease pronation.

A method to indirectly measure the tibial rotation and
subtalar joint pronation during stance is the ground
reaction torque. The ground reaction torque about the
vertical axis has been studied in walking and running.
Mann(30) and Root(40) have postulated that this torque is a
direct response to tibial transverse plane rotation. This
appears to be true during walking, as Ramakrishnam and
colleagues(38) found the ground reaction torque to be
internally directed during the first 40% of stance phase,
and then switched to externally directed during the
remainder of stance phase. This would coincide with the
tibial internal and external rotation motion that is
occurring. ‘

Holden and Cavanagh<21) studied the ground reaction
torque during running in ten male runners. The authors
concluded that the rationale used to explain ground reaction
torques during walking could not be applied to running.
Holden and Cavanagh postulated that ground reaction torque
in normal running acts to resist foot abduction during the
first 60-70% of support, when pronation is known to occur
since foot abduction is a component of pronation. During

the remainder of support phase the ground reaction torque

14
resisted adduction. The authors also noted that when the

subjects were footwear that increased pronation a subsequent
increase in the ground reaction torque tending to resist
foot abduction occurred. The above explanation of the
ground reaction torque allows an investigator to use the
ground reaction torque as an indirect method of measurement
of tibial rotation during walking and subtalar joint

pronation during running.

III . EXPERIMENTAL METHODS

A general description of the experimental methods and
techniques used to collect and reduce the data are described
in this chapter. All collection was performed at the
Biomechanics Evaluation Laboratory, Saint Lawrence Hospital,
Lansing, Michigan. Three types of information were
experimentally recorded: kinematic activity of the lower
limb; kinetic ground reactions; and surface
electromyographic signals from six lower extremity muscles.
Equipment

Video data were collected using four solid state,
shuttered video cameras. Data collection rate was 60 frames
per second at one millisecond per frame. All four cameras
were synchronized by a VP-320 model dynamic processor. The
cameras were positioned to optimize viewing of the targets
placed on the right lower extremity of the subjects.

A calibration space consisting of twelve targets of
known position was placed in the field of view of the
cameras. The calibration space (see Figure 1) measured
182.88 X 121.92 X 114.3 cm. The calibration structure
provided a known coordinate sytem to define the space of the
viewing area. The center of the force plate was the origin
of the coordinate system. Each target in the calibration

space was covered by retro-reflective tape (3M Scotchlite

15

16

 

Figure 1

Calibration space

17
Corporation). Illumination of the targets was provided by a

single flood light attatched approximately two inches from
the center of each camera lens. The proximity of the flood
light to the lens was required to achieve the maximum
intensity of the reflected light. The retro-reflective tape
is extremely sensitive to the "observation angle" which is
defined as the angle between the incidence light ray, the
reflective target, and the reflective ray returning to the
camera lens. An increase of one degree in observation angle
causes a 16 fold reduction in the intensity of the reflected
light.(44)

The calibration space was filmed and each target
location was digitized using the Expertvision<33) three
dismensional (EVBD) digitizing program. The EVBD digitizing
Program calculates the centroid location of each target.
Using the method of direct linear transformation developed
by Walton(48), the transformation matrices were determined
and stored in the environmental operator section of EVBD.
The accuracy of the calibrated space was reported as a "norm
of residuals" for each camera. The residual values were
less than .38 for all testing sessions. This fell below the
system requirements for residual values of less than 2.0,
indicating an accurate calibration space.

Ground reaction forces (Fx, Fy, F2) and the ground
reaction torque (M2) were measured using an AMTI
Biomechanics Force Platform Model OR6-6. The force platform

incorporates strain gages which measure the applied forces

18
and moments, amplify the signal and then send it to the

analog to digital converter. The signal was sampled at a
rate of 1000 Hz and stored on the Sun 4 work station (see
Figure 2). The orientation of the force plate and
laboratory coordinate systems are shown in Figure 3.

The electromyographic signals were collected via
surface electrodes and telemetered to a Transkinetics
receiver. The signals for each muscle were stored on the
Sun 4 workstation.

Subjects

The subjects of this study were male graduate students
at Michigan State University. None of the subjects were
presently performing long duration backward locomotion on a
regular basis. All but one subject was presently engaged in
sports (basketball, football, karate) which required
backward movement. The subjects were void of previous knee
trauma or pathology. Table 1 describes the individual
subjects traits. The subjects wore their normal jogging

shoes during the testing.

 

Table 1
Individual subject traits
Subject # Height(cm) Weight(kg) Age(yrs)
F1 192 82.4 24
F2 183 89.8 28
F3 180 69.0 28
F4 172 64.5 33
F5 185 84.5 28
F6 170 63.1 31

 

Mean i sd 180.3 1 8 75.6 i 11 28.7 i 3

 

Figure 2

Sun 4 workstation

 

 

Lz
Ly
9Y4 . LX
‘ 'pz
(Px, Py, P2) = Force plate coordinate system
(Lx, Ly, L2) = Laboratory motion coordinate system

Figure 3

Force plate and laboratory coordinate systems

20
Prior to testing the subjects signed an informed

consent and were briefed on the testing sequence. Motor
points of six muscles on the right lower extremity (rectus
femoris, vastus lateralis, vastus medialis, biceps femoris,
gastrocnemius, and tibialis anterior) were located. Exact
electrode placement was determined using a Chatanooga
(Chatanooga Corp., 101 Memorial DR., Chatanooga, TN 37405)
Intelect model 500 neuromuscular stimulator (see Figure 4).
The points were identified and the area was prepared by
shaving the region with an electric razor and then wiping it
several times with a dry cloth to remove skin oils. In
order to minimize cross talk between muscle groups the
electrodes were placed approximately 1-2 cm apart over the
motor point of interest.(5) The electrodes were attatched
to the transmitters and secured on the subjects right lower
extremity with self adhesive tape. Once all electrodes and
transmitters were in place a manual muscle test was
performed on each of the six muscles while monitoring for
the appropriate activity. If the signals were weak or
absent, modification was made.

Seven 2.54 cm diameter and two 1.27 cm diameter retro-
reflective spherical targets were placed on specific
locations on the subjects pelvis, right lower extremity, and
right shoe. Target size was chosen to maximize the
efficiency and accuracy of the automated digitizing system.
The EV3D digitizing system sweeps across a 240 X 256 pixel

grid on the video image and computes the average of the

21

 

Figure 4

Neuromuscular stimulation of motor points

22
centroid of each target. The larger targets provide a more

accurate centroid due to greater pixel surface area in which
to average the centroid. Conversely if the targets were too
large, merging of two targets would occur and result in the

centroid of the merged spheres to be calculated as a single

target. Table 2 gives the target number and anatomical

location of each target. Target positions are shown in

Figure 5.
Table 2
Target number and anatomical location
Ianggt_fi Langmagg (gn Eight sige Qf thx)
1 Anterior superior iliac spine
2 Posterior superior iliac spine
3 Greater trochanter
4 Lateral femoral condyle
S Anterior tibia (at level of proximal
gastrocnemlus tendon)
6 Posterior shank (at level of proximal
gastrocnemius tendon)
7 Superior calcaneus (SUperior heel counter of
shoe)
8 Inferior calcaneus (inferior heel counter of
shoe)

9 Distal lst metatarsal (on shoe)

23

 

Figure 5

Target locations on subject

24
Data collection

The subject stood on the force plate in a relaxed
position with the knee joint in neutral (neither flexed nor
extended). Five seconds of video data were collected and
stored. This file was used to calculate the offset knee
angle. This step allowed the linkage targets to be
independent of an exact vertical or horizontal position.

Three trials of four different conditions were randomly
tested. The conditions were: walking forward, walking
backward, running forward, running backward. A trial
consisted of a subject's right foot landing entirely on the
force platform. A mistrial occurred if the subjects stride
was unnatural or if the subject altered his stride in an
attempt to hit the force plate. The trials were collected
using the Beldata software program(49) which allowed
simultaneous collection of force plate, kinematic, and EMG
data. When the force plate was triggered at the instant of
vertical loading, an event marker was placed on each raw
video and EMG file to allow synchronization of all
components. Immediately after the trial the ground reaction
forces and EMG results could be viewed. Three successive
trials could be overlayed and viewed. Figure 6 demonstrates
the reproducibility of the force data during three
successive trials in subject F2 walking forward.

Following successful completion of all trials, the
video files were transfered to the EV3D program for

digitizing and further analysis.

25

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Figure 6
Reproducibility of Z - force data

IV . ANALYTICAL METHODS

Each video file was tracked using the track operator of
the EVBD software. The stick figure option was utilized
allowing the targets to be tracked as rigid links. Each
target had a three dimensional path of motion. The target
paths were smoothed using the EV3D track editor operator.
The edited files then underwent the following analysis.

The knee angle was defined as the angle between the
femur rigid link (targets 3-4) and the shank rigid link
(targets 5-6). An offset angle was calculated from the
standing file allowing the knee angle to be independent of
exact placement of the targets. The EV3D angle operator
calculated the knee angle. Each knee angle file was then
differentiated to produce a knee angular velocity file.

Target 4 was assumed to be the saggital plane knee
joint center and the X (X4) and z (Z4) coordinates of this
target in laboratory space was required during each instance
of foot contact with the force plate. The location of
target 4 and the knee angular velocity file (m) during
stance were exported to the Belcalc(50) and Ca1c_twf(51)
programs. The force plate Y force (Fy) and Z force (Fz) as
well as the Y coordinate of the center of pressure (COPy)
were combined in the following manner to calculate the knee

muscle moments.

26

27

(1) Moment = (-Fy -Z,) + (F2 - on -COPy))

The muscle power was then calculated by equation (2).

Equation (3) will yield the work performed by the

muscles.

't
(3) W = .[ Ptt')dt'
0

The synchronization of the kinetic (1000Hz) data and
the kinematic (60Hz) data was accomplished by taking kinetic
data at each 16 millisecond time interval.

The mean peak positive and mean peak negative power was
computed from 3 trials of each condition for each subject.
Within subject analysis of forward walking-rearward walking
and forward running-rearward running was performed with a
paired student t-test with a level of significance of
p<0.05.

The mean negative and positive work was analyzed in the
same manner.

The EMG signals for the six muscle groups were subject
to the following analysis. First, the mean pattern of
muscle activity was determined and graphed in percent of

stance phase. Second, the mean duration of total on time

28
was determined and expressed in percentage of stance phase.

The final step compared the mean duration of on time within
the forward-rearward walking and running conditions
utilizing a paired student t-test with a level of
significance of p<0.05.

The ground reaction torque was subjectively compared
for direction and timing during stance phase of each
condition.

An overall picture of motion, forces, and muscle
activity and the clinical significance of these is then

presented.

‘V. RESULTS AND DISCUSSION

The following chapter is subdivided into a walking and
running section. The results of the knee joint muscle
moment, power, and work are presented. The EMG activity and
ground reaction torque are also presented. Each of the
graphs represent the right stance phase of gait. Time zero
corresponds to foot strike (0% stance).

An example of the calc_twf program output for subject
F5 walking forward right is given in Figure 7. These
figures demonstrate the combined force and motion data with
resultant knee muscle moment and muscle power numerical
output.

IALRING

The knee muscle moment curves for the six subjects
walking forward are presented in Figure 8. Each graph shows
_the three trials from each subject. Extension of the knee
joint is positive (+) and flexion is negative (-).

The shape of the forward walking knee muscle moment
curves compare favorably with the results of previous
authors.(l,38,53,54,57) The knee joint moment demonstrated
a momentary flexor pattern during the first few percent of

stance, followed by a extensor response which assisted in

29

Kine-utlc .rid tile nnec:
Kine-«tic .tcd file nnee:

Kineeatlc .811 file none:
Force file nnee:

Target 4:

71:0 x coord z coord
(sec) 1e) 1!)
-0.050 -0.3295 0.5455
-0.033 -0.2995 0.5426
-0.017 -0.2631 0.5117
0.000 -0.2354 0.5409
0.011 -0.2043 0.5411
0.033 -0.1734 0.5127
0.050 -0.1431 0.5452
0.067 -0.1144 0.5474
0.083 -0.0888 0.5485
0.100 -0.0676 0.5480
0.117 -0.0508 0.5468
0.133 -0.0375 0.5457
0.150 -0.0264 0.5451
0.167 -0.0170 0.5450
0.183 -0.0087 0.5450
00200 -000012 0.5452
0.217 0.0059 0.5456
0.233 0.0127 0.5465
0.250 0.0191 0.5477
0.267 0.0252 0.5432
0. 28:1 11.02110 11. 5508
0.300 0.0365 0.5521
0.317 0.0124 0.5538
0.333 0.0159 0.5549
0.350 0.0561 0.5556
0.367 0.0649 0.5558
0.383 0.0712 0.5559
0.400 0.0343 0.5561
0.417 0.0954 0.5565
0.433 0.1079 0.5569
0.450 0.1221 0.557
0.467 0.1381 0.5568
0.483 0.1570 0.5561
0.500 0.1778 0.5551
0.517 0.2012 0.5537
0.533 0.2275 0.5517
0.550 0.2573 0.5487
0.567 0.2908 0.5446
0.583 0.3284 0.5392
0.600 0.3698 0.5329
0.617 0.4117 0.5262
0.633 0.4622 0.5201
0.650 0.5118 0.5154
0.667 0.5624 0.5129
0.683 0.6076 0.5126
0.700 0.6667 0.5128
0.717 0.7128 0.5192

30

1561r11.v1d
15w1r1.ind
15uIrIK.dif
42.1pt

8 LAT FEM CON

angular velocity

7 force

1red/eec1

2.0307
3.0303
2.5125
2.2502
2.3093
2.5553
2.7551
2.5139
1.9223
1.0110
0.2514
'0.2403
'0.5004
'008364
-009639
“1.0419
'1.1359
-502166
‘1.3537
“1.3005
'1.2433
'1.1707
'1.2121
‘1.2551
-7027“:
“1.1000
‘Q.5151
'0.5720
'0.3119
'0.0515
0.2413
0.5242
1.0205
1.3721
1.0574
2.0023
2.0355
3.4542
4.4217
5.1557
5.5435
5.5409
5.4955
5.2115
0.0050
5.5750
0.0000

18)

14.2832
15.0405
15.7905
21.0205
47.0908
’9800122
-80.9758
~105.1963
-147.8335
-168.7163
-170.9639
-158.9243
-143.1748
-120.7607
-106.5474
-92.2632
-77.9976
~68.9829
-56.2176
-41.9932
-36.7319
~29.2471
-21.0395
-12.8232
-3.1289
7.3257
16.2983
28.9932
43.1611
58.8037
79.6484
504.2285
125.1157
73502500
161.6699
176.5273
186.8745
184.5141
163.5517
132.2163
94.1318
57.5034
20.8628
-3.0420
-1.5210
-3.0278
-0.7720

a force

(I)

-20211.
-z.2aoo
'2.1541
45.5220
295.4534
390.5915
537.0715
500.5449
551.0001
759.3153
915.4350
952.3535
995.1554
954.5910
932.3045
550.3193
753.2557
715.7355
557.3510
522.5347
593.4445
575.1025
501.7452
502.2232
505.0935
559.9350
023.0325
571.0995
719.2451
755.5015
795.2197
529.1372
552.9321
551.5701
505.5715
503.0720
504.4444
703.5207
555.2359
410.4325
275.1055
151.5142
57.4455
17.4790
2.5799
2.7555
'0.0723

Figure 7 Program.0utput ca1c_twf

! cop
1-)

0.5201
0.5454
0.5591
0.1225
0.1221
0.1053
0.0954
0.0835
0.0573
0.0553
0.0197
0.0441
0.0307
0.0252
0.0175
0.0031
'0.0125
'0.0255
-0.0425
-0.0531
-0.0012
-0.0550
'0.0709
-0.0740
-0.0705
-0.0784
'0.0795
-0.0803
'0.0510
-0.0823
-0.0825
-0.0837
'0.0551
'0.0575
'0.0895
'0.0924
'0.0955
-001009
-001087
'0.1155
'0.1255
-0.1352
-0.1421
'0.1795
-0.0797
0.0441
3.5559

Tine
'laecl

0.1117

1L033

0.050

0.067 .

0.083
0.100
0.117
0.133
0.150
0.167
0.183
0.200
0.217
0.233
0.250
0.207
0.283
0.300
0.317
0.333
0.350
0.367
0.383
0.400
0.417
0.433
0.450
0.467
0.483
0.500
0.517
0.533
0.550
0.567
0.583
0 . 600
0.617
0.633
0.650
0.667
0.683
0.700
0.717

Doucut
(8'01

'50.0250
0.2135
19.0951
39.0290
55.4350
53.5433
92.4502
93.1951
55.2522
75.5132
55.3133
51.9597
37.3349
20.3109
15.1315
7.3519
202"23
-101113
“4.3505
“5.9915
“9.5100
-4200288
“12.3735
“13.4334
“13.5768
“13.3505
“13.1471
“12.5953
-7.5017
”100205
9.1719
19.2773
27.3519
33.1010
30.2279
34.1915
29.0517
19.0450
10.4515
5.2533

2 . 30110
3.5205
0.0849

power
(watts)

118.5302
-0.5528
-53.2478

“102.0155
-3210104'

-84.4643
~24.1724
22.9521
52.9935
64.2443
63.8875
54.1481
42.5215
33.6337
21.3520
10.1"132
2.8376
-1.3783
-5.3169
-9.0061
-12.5212
'13.3035
-10.4614
-7.6843
-4.2659
-0.7318
3.2123
7.9265
7.8027
1.1002
-15.4770

-39.7558..

-72.0871

-115.5407
-160.1871
-176.3831
-166.0361
-110.8325

-57.6014
-43.2619
-13.8131
-24.2073

-0.0000

Figure 7 (cont'd.).

31

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Figure 8 Forward Walking Knee Muscle Moment Curves

 

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"no (not)

MT FE” CON

 

 

—
Figure 8d Subject F4

Figure 8 (cont'd.).

36

 

fbmworwoa é'uahado’on Xa'J-oeadwvy

 

 

 

 

III-III (III)
é

 

0 too 25 360 460 can can 75 too
""0"“’ twrnnta:

 

 

 

Figure 8e Subject F5

Figure 8 (cont'd.).

37

 

 

 

 

 

 

flwmwdorwot é’mfioa'é’on fahwotoay
am
300+
190‘
100‘
am
In M
+ 40‘ ' ‘
.
-Qoo4
- ““1
i -m
l
- 6 150 255 JR 703 W 060 75 Too
nmoun) thucaw
_

Figure 8f Subject F6

Figure 8 (cont'd.).

38
arresting knee flexion as full weight bearing occurred.

During late stance a slight flexor moment occured before a
second extensor moment was seen during terminal stance. The
forward curves demonstrated low intrasubject variability.
Higher variability was noted across subjects. Winter (54)
described the increased intersubject variability to be
higher at slower speeds. He postulated that this was a
result of the fact that one's natural cadence is
accomplished at a subconscious level and well within the
extremes of forces possible at each joint. As speed
increases higher joint forces are achieved, and a conscious
over-ride of the loose walking patterns is necessary.

The knee muscle moment for the six subjets walking
rearward are presented in Figure 9. Each graph shows the
three trials from each subject for the respective condition.
Extension of the knee joint is positive (+) and flexion is
negative (-). In rearward walking the knee mwxfle moment
demonstrated an extensor dominance throughout stance phase
in all subjects walking rearward. The magnitudes of the
muscle moment were consistently lower than those noted in
forward walking for the same subject. The rearward walking
knee muscle moment patterns demonstrated consistency within
subject trials with increased variability across subjects.

The representative sample of the knee muscle power
curve for each of the six subjects walking forward are
presented in Figure 10. A positive value indicates

concentric knee extensor muscle activity or eccentric knee

39

—
inmwlavw’» é‘mlaaé’ow Xa‘oaabw

 

am

0004

1&1

 

 

 

~100
«so
‘3‘
i -m
l -...
3 95 zoo 33 To? iii «To 160 .66

“"0"” nurmcou

 

 

Figure 9a Subject F1

Figure 9 Rearward Walking Knee Muscle Moment Curves

40

00'

.9 ' mocha“); é'u-oéoob‘o‘ow foMoJowy

 

 

 

 

 

«no
«col
?
5 «no
I .aq J
T to? 260 33 3 iii can 760 one
""0"“’ ldffllam

 

 

Figure 9b Subject F2

Figure 9 (cont'd.).

41

 

 

 

 

 

 

fundam.» Jmhoé’on gal-awake}
m4
”4
1801
mm
.94
o M
o 40‘
I
-...J
.'“J
‘ ?
é -aoo
l -,,..
3 150 25 do 700 if); 060 750 So
“(m’ n ur rsu cow

Figure 9c Subject F3

Figure 9 (cont'd.).

42

Jumoolmwuzos 500M560» Xohaadoaoy

 

um

i001

'N*

”*

 

 

 

 

 

 

“"“"“’ Lawmucm:

 

 

 

Figure 9d Subject F4

Figure 9 (cont'd.).

43

“

ibmw‘awo’os é'ualuod‘on Xohoofwyy

 

9.01

100‘

-1M

 

 

 

truth-c)

 

 

Figure 9e Subject F5

Figure 9 (cont'd.).

44

350-0000400609 é'u-ohoé’o-n £040!»th

150‘

 

M1

1.0%

 

 

-1”: .

 

 

 

 

 

Figure 9f Subject F6

Figurc 9 (cont'd.).

45

fmeovw'u é'uohodéon Zo‘omfow

 

 

 

 

 

6 IE :70 $0 460 do ch 75
“”0"“’ nrnwwucav

“

Figure 10a Subject F1

 

 

Figure 10 Forward Walking Power Curves

46

.9“ "Melanie; é‘mfindo‘ow Xohowhay

 

hulk. k Coda. - ".81.
m?” Hafiz) - -2&M7I

1.“
IN‘

M¢

 

 

 

Ldmun

 

 

Figure 10b Subject F2

Figure 10 (cont'd.).

47

A?

“momma é'MMé‘on 3&5.th

 

MN «on ) - noon
m m ‘) - a...“

”01
um

IGO‘

 

 

 

v— r ‘7 —Y—

no no no do too do no too
""0"“’ aruuwucav

—
Figure 10c Subject F3

 

 

Figure 10 (cont'd.).

48

m
fléomooflavwos é'whato‘ow Iodooadooy

 

MIN. out who) - “.0.
m M ) II 40.00:.

M (uh)
I
§

 

 

 

'7‘ ‘V— fi— fi

6 :63 .27» no coo ooo ooo 7o? .60
""" """°’ at m: cow

 

 

Figure 10d Subject F4
Figure 10 (cont'd.).

49

.9 ' Mona» €uohaé$¢w role-coho,»

b.

 

mum )- um
MM )- ~23.“

 

 

 

 

MT “I.”

 

 

Figure 10e Subject F5
Figure 10 (cont'd.).

50

u _
meoo‘aow'oo é‘u-ahado’ow .t’oloooo‘ooy

 

am ) not

My. out Coulo- -
WMM)- 48.17“

3.04

100*

 

 

 

6 T6 53 :60 do o6o oéo woo
""°"" llIICGM

 

 

 

Figure 10f Subject F6

Figure 10 (cont'd.).

51
flexor muscle activity. Conversely, a negative value

indicates eccentric knee extensor muscle activity or
concentric knee flexor muscle activity.

The shape of the forward walking power curves compared
favorably with Zarrugh(57) who predicted joint power based
on kinematic data only. Generally, there were low power
requirements in the knee during forward walking. The power
curve begins in a positive direction then demonstrated a
negative braking phase during early stance, which was
followed by a moderate positive phase corresponding to the
swinging fOrward of the contralateral limb, finally there
was another relatively large negative phase which
corresponded to the flexion of the knee in late stance.

The representative sample of the rearward walking knee
muscle power curves for each of the six subjects are
presented in Figure 11. A positive value indicates
concentric knee extensor muscle activity or eccentric knee
flexor muscle activity. Conversely, a negative value
indicates eccentric knee extensor muscle activity or
concentric knee flexor muscle activity.

The rearward walking power curves showed low power
requirements throughout stance. Five of the six subjects
demonstrated two positive peaks, one during initial stance
and one during late stance. The knee muscular contribution
to braking in rearward walking was apparently with

concentric quadriceps activity which contrasts with the

52

—

3&0- moMoMu é'uohod'ow Xohwho’o

 

1.04

tool

 

 

 

VIII-o (no-o)

 

 

Figure 11a Subject F1

Figure 11 Rearward walking Power Curves

53

—
flbmoo‘oou'oo é'whoé’oo [ohwboy

 

 

 

 

""0"“’ nonwun

 

 

Figure 11b subject F2

Figure 11 (cont'd.).

54

 

 

 

 

 

 

 

fibuoofiam d‘uohoé’oo fo‘om
aw
PoolNo-ortoqloo - on“
hfiomOodoz)- 432“
m4
100‘
”0‘
Hi
“i ‘ J\/
I *J
o
4004
«w
1-...
6 :6o 26o 36o o6o o6o o6o 76o
""0"“’ nouwmucav

Figure 11c Subject F3

Figure 11 (cont'd.).

55

 

 

 

 

 

 

£bmoo‘ovubo Jot-abattoir. role-1,4501?
*4
MM out Owl-o - um
m. out (loud-3) - -2oozo
m4
100‘
tfi'
av
0‘ M M
a .u‘
o
-1oo~
«w
3. -aoo
5 1h 2“ 30 do & Ch 77” ooo
"'"‘ 9"“) at In: con

Figure 11d Subject F4

Figure 11 (cont'd.).

56

M

ibmoolvcwwoo é‘mhab‘o‘ow .l’olomtoay

 

new. work Gaucho) - “.7012
m M 0m) - a“

 

 

 

6 16o 26o 86o o6o o6o o6o 76o
""0"“, axrnutoc

——_______—_l

Figure 11e Subject F5

 

 

Figure 11 (cont'd.).

57

ibmw‘avweo Jwémd‘ow .flo‘osoo‘ooy

80‘

 

III-Choctaw - OJ!”
”maul-A- 4.0020

am
'I.*

m&

 

 

 

 

 

Figure 11f Subject F6

Figure 11 (cont'd.).

58
eccentric quadriceps activity of braking present during

forward walking.

Table 3 presents the average peak positive power of
three trials for each subject during the forward walking and
rearward walking conditions. A paired students t- test
demonstrated no significant differences in peak positive

powers between conditions.

 

Table 3
Average peak positive power - walking
(Watts)
Subject 9 Forward Rearward Difference
F1 118 86 32
F2 81 135 ~54
F3 129 67 62
F4 53 36 17
F5 104 124 -20
F6 57 9O -33
X0 = 0.7 SD = 44 t = .039

Table 4 presents the average peak negative power of
three trials for each subject during the forward and
rearward walking conditions. A paired students t- test
demonstrated significantly (p<.05) greater peak negative
values during the forward walking condition. The peak
negative value in forward walking occurred during late
stance and was primarily due to concentric activity of the

hamstrings and gastrocnemius muscles.

59

 

Table 4
Average peak negative power ~ walking
(Watts)
Subject # Forward Rearward Difference
F1 ~209 ~21 ~188
F2 ~204 ~59 ~145
F3 ~461 ~60 ~401
F4 ~162 ~25 ~137
F5 ~181 ~28 ~153
F6 ~151 ~23 ~128
XD = ~192 SD = 104 t = ~4.522

p<.05

Integration of the power curve will yield the joint
muscle work. Table 5 presents the average positive work of
three trials from each subject during the forward and
rearward walking conditions. A paired students t- test

demonstrated no significant differences between conditions.

 

Table 5
Average positive work ~ walking
(Joules)
Subject # Forward Rearward Difference
F1 9 10 -1
F2 11 10 1
F3 15 7 8
F4 6 6 0
F5 9 16 -7
F6 .3 13 ~10

x0 = -1.5 sD = 6 t = -.612

60
Table 6 presents the average peak negative work of

three trials from each subject during the forward and
rearward walking conditions. A paired students t- test
demonstrated significantly (p<.05) greater negative work
during the forward walking condition than during the

rearward walking condition.

 

Table 6
Average negative work ~ walking
(Joules)
Subject # Forward Rearward Differences
F1 - ~30 ~2 ~28
F2 ~27 ~1 ~26
F3 ~43 ~7 ~36
F4 ~21 -2 ~19
F5 ~24 ~1 ~23
F6 ~14 ~1 ~13
X = ~24 S = 8 t= ~7.348
D D p<.05

The EMG activity from the muscles surrounding the knee
joint were analyzed. The active muscles should be
responsible for the knee power generation and absorption
requirements. Figure 12 shows the firing pattern for each
of the six muscles studied during the stance phase of
forward walking from heel strike (HS) to toe off (T0).
Figure 13 shows the firing pattern for each of the six
muscles studied during the stance phase of rearward walking
from toe strike (TS) to heel off (HO). Figures 12 and 13

show the average pattern from all six subjects. .For ease of

61

Rectus Femoris

Vastus Lateral is

Vas tun Medialis

Biceps Femoris

Gas trocnemius —

 

Tibialle Anterior

 

  
 

u; in 56 So 30 éo'giéo 13* 60 50 60
t Stance Phase
Figure 12 Forward walking EMG pattern
Rectus Femoris
Vastus Lateralis
Vastus Medialis
Biceps Femoris _
Gastrocnemius _-
Tibialis Anterior —

 

 

rs i0 26- 50 ob 56 6b 10 so 90 35
\ Stance Phase

Figure 13 Rearward walking EMG pattern

62
viewing the direction of travel is from left to right in

both figures.

Table 7 presents the mean muscle total on time and
standard deviation (sd) across subjects in % of stance phase
for each muscle during the forward and rearward walking
conditions. A within subject paired students t-test with

the appropiate level of significance is presented for each

 

muscle.
Table 7
Total on time for individual muscles ~ walking
(,% )

Muscle Forward Rearward t-level p<
Rectus femoris 16 i 4 58': 23 ~4.719 .01
Vastus lateralis 19 3,12 82 i 6 ~13.498 .001
Vastus medialis 23 1'5 83 i 5 ~25.46 .001
Biceps femoris 37‘: 10 21': 7 3.989 .02
Gastrocnemius 48 i 18 35 i 18 1.027 ~
Tibialis anterior 22‘: 15 43 1.25 ~2.784 .05

The EMG muscle firing sequence presented in Figure 12
is consistent with the literature (5). A comparison of the
forward walking EMG signal with the rearward walking signal
demonstrated a marked increase in total on time of the three
knee extensor muscles (rectus femoris, vastus lateralis, and
vastus medialis) during the rearward walking condition
compared to the forward walking condition. Comparing the
EMG activity to the muscle moment and power curves suggested
primarily concentric propulsion activity of the knee

extensors in rearward walking with periods of isometric

63
stabilizing activity through the first 80% of stance phase.

This contrasts sharply with the forward walking conditions
where the knee extensors are acting primarily as eccentric
shock absorbers during early stance phase.

The biceps femoris showed greater inconsistent activity
both within and across subjects. The biceps femoris muscle
activity demonstrated a statistically significant increase
in total on time during forward walking as compared to
rearward walking. In forward walking the biceps femoris was
active during early stance cocontracting with the knee
extensors. In rearward walking the phase of biceps femoris
activity that was consistent across subjects was during late
stance phase.

No statistically significant differences were noted in
gastrocnemius total on time between conditions, but a marked
change in the type of muscular contraction and function was
noted. In forward walking, the gastrocnemius acted
primarily concentrically from mid to late stance assisting
with propulsion of the limb forward. This contrasts with.
rearward walking where the gastrocnemius appeared to be
acting eccentrically during the first portion of stance.
This would allow the gastrocnemius to function primarily as
a shock absorber via the ankle joint during weight
acceptance in rearward walking.

The tibialis anterior demonstrated a statistically
significant increase in total-on time during rearward

walking. In forward walking the tibialis anterior

64
functioned eccentrically in early stance to allow a

controlled lowering of the foot to the floor. In rearward
walking the tibialis anterior appears to act concentrically
from mid to late stance functioning to raise the foot from
the floor.

The resultant ground reaction torque is presented in
Figure 14. This is a representative sample from subject F2
comparing forward walking (red) to rearward walking (green).
A positive value coincides with the limb externally
(laterally) rotating relative to the force plate, conversely
negative values coincides with the limb internally (medial)
rotating relative to the force plate. The forward walking
torque was consistent with the literature (30,38),
demonstrating a sinusoidal like curve begining as an
internally_directed torque at heel strike until
approximately 50% of stance then becoming externally
directed for the remainder of stance. The rearward walking
torque is externally directed until approximately 70% of
stance then a short small amplitude internally rotated
torque which returns to an externally directed torque in the

final 10% of stance.

E1712

ZED-4

mmmamz.

18

)1

65

 

 

 

l 1 L4
I'Ir ""'{r ‘1

'-

 

u

—1s

‘lrja

 

 

8.3

1111

Ground reaction torque forward vs rearward walking

1117

 

8.1

 

 

1111

 

 

1111

 

FDRNQRD-RED RERRNRRD-GREEN

Figne l4

 

8.?

66
RUNNING

The knee muscle moment curves from the six subjects
running forward are presented in Figure 15. Each graph
shows the three trials from each subject for the forward
running condition. An extension muscle moment of the knee
is positive (+) and a flexion muscle moment is negative (~).

The shape of the forward running knee muscle moment
curves compare favorably with Winter's(54). The knee muscle
moment was entirely extensor through the stance phase of
running. The shape of the moment curve was consistent
across subjects, but the magnitudes varied. The large
magnitude of the knee extensor moment in subject F3 possibly
represented a mechanical inefficiency in this
subject, since he was the only subject that had not
previously jogged with any regularity.

The knee muscle moment curves for the six subjects
running rearward are presented in Figure 16. Each graph
shows three trials from each subject in the rearward running
condition. An extension muscle moment is positive (+) and a
flexion muscle moment is negative (~).

The rearward running knee muscle moment patterns vary
considerably with their forward running counterparts. The
rearward running knee muscle moment consistently displayed a
two stage pattern beginning with a brief extensor period
from toe strike until 25% of stance, followed by a second

larger extensor moment from 50-100% of stance. The

67

_——--——---_-T

fibmda'néoo 6.04%ka .l’olomb‘ooy

 

nee
noel
no»J

301
”01
1001

01

-I
-1W

 

 

unanouo
l
i

 

6 if :66 :69 :66 160 360 36 3o 466 oéo
M 0"“) n w m can '

 

 

—
Figure 15a Subject F1
Figure 15 Forward Running Knee Mbscle Moment Curves

68

———_—_'_—_F

Inflow.» é'mhod‘ow {ole-solo”

 

Wok-I)
i
3

 

 

 

5 36 lb 163 16o 30 3% in 45 oE W
“M Le! m can

 

 

Figure 15b Subject F2

Figure 15 (cont'd.).

69

.959 “Mono?” é'uoluoébn .t’o‘oeoodoey

 

é

 

 

 

 

 

Figure 15c Subject F3
Figure 15 (cont'd.).

7O

—

fikmwfiovwbo Jmhoé’on {whom

 

1300‘
12M‘
HN‘

3 :39:
l .93”

4...)

 

 

 

6 i If Ii. :50 33 I“ 83 460 45 0b
"‘“'” ouwwucau

—
Figure 15d Subject F4

 

 

Figure 15 (cont'd.).

 

71

meoalovu‘ea é'uobafi'ow {aheahef

 

‘ - ‘ O
A A L A A

44

A L A A A - A

:8
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éiéiiéé

«ow
-uoo(
-1m4
~13“

 

 

6 66 :60 :5 25 :60 no i Too $66
"”3“” autumn:

Figure 15e Subject F5

Figure 15 (cont'd.).

 

 

72

—

mewdavwoa é’u-ohaé’ow 43'th

 

 

 

-11”
-12”

 

“"0"“’ tJmucam

 

 

Figure 15f Subject F6
Figure 15 (cont'd.).

73

m
.9me006» é‘uofioad‘ow £040an

 

III-0‘05“!)
0
3

 

 

 

6 ii an .a db 33 oh 33 (do .5 db
""0"”’ ntnwmucau

 

 

—
Figure 16a Subject F1
Figure 16 Rearward Running Knee Muscle Moment Curves

74

fihmoolvono‘oo é‘u-ohad‘on Xahoahey

ilfli
new
HU‘
wool

 

éééétiéééessssmu

I“ Mon)

 

 

 

6 0'0 :5 160 :60 260 :60 lo 460 45

m (moo) Let mo Con

Figure 16b Subject F2

 

 

Figure 16 (cont'd.).

75

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fiummme dendo’ow 430405.010”;

 

"fl‘

 

 

 

—tlfl( '
6 oo uh 160 760 :60 35 i3 460 466 o6o

"'""'""" «urn-con

 

 

Figure 16c Subject F3

Figure 16 (cont'd.).

76

flumMaMoa d’mbaé’ow foheaboy

 

400+
-3901
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-m4

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-neo

l 42001
am

 

 

 

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Figure 16d Subject F4

Figure 16 (cont'd.).

77

M

ibmmvwoa 6.044304%» gateway

 

O+

 

 

 

 

 

Figure 16e Subject F5

Figure 16 (cont'd.).

78

F————

”kmwflo'woo Jmhodow Xa‘oookoy

 

13ml

wool

 

 

 

6 15 26o :66 06o IT» o6o 16o 36

“"0"“’ Lawucan

Figure 16f Subject F6

 

 

Figure 16 (cont'd.).

79
magnitude of the knee muscle moments in rearward running

were consistently lower than those noted in forward running.

The representative sample of the knee muscle power
curves from each of the six subjects running forward are
presented in Figure 17. A positive value indicates
concentric knee extensor muscle activity or eccentric knee
flexor muscle activity. Conversely, a negative value
indicates eccentric knee extensor muscle activity or
concentric knee flexor muscle activity.

The shape of the forward running power curves compare
favorably with Winter's(54) results. During stance phase
there were two distinct phases. The first power phase began
immediately after heel strike and continues until mid
stance. This phase was a shock absorbing phase controlled
by eccentric activity of the knee extensors. The second
power phase, acted to propel the limb forward from mid
stance until push off, and was a function of the concentric
activity of the knee extensors.

The representative sample of the knee muscle power
curves from each of the six subjects running rearward are
presented in Figure 18. A positive value indicates
concentric knee extensor activity or eccentric knee flexor
muscle activity. Conversely, a negative value indicates
eccentric knee extensor muscle activity or concentric knee
flexor muscle activity.

The rearward running power curves demonstrated a four

phase pattern. The first phase was a small amplitude

80

A
36000400609 (farahoé'oo Xohmboy

 

uoo
noel new. out ) - nnoo

In.“ eon ) n 44.”!
noo‘

wool

 

 

 

 

 

Figure 17a Subject F1

Figure 17 Forward Running Mbscle Power Curves

81

fbmoe‘ovwoo 6304941509» few

new
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noo m M ) - m

‘M'

 

. A A A A A

4A

 

 

 

6 oo lb Iio 26o 33 37‘! in 36 do
"”0"“, Lurunam

 

 

Figure 17b Subject F2

Figure 17 (cont'd.).

82

fi
fumodouu Juohoé'ono fa‘oww

 

2"” mason

now-m -
‘mi Hue-tactic)- ”7

oooo‘

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A

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Figure 17c Subject F3

 

 

Figure 17 (cont'd.) .

 

83

meodono'eo Jun-abode» 4416940601?

 

uool
aani
wool
”Mi

 

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m loot Oouloo)- «moo:

 

 

 

Figure 17d Subject F4

Figure 17 (cont'd.).

84

m
.960- moa‘ovu’oo Juohafiow JO‘O‘DGJOW

 

enou- cert Coulee) - moon

I”. out (joules) - 4.22“
Hfl‘

 

 

 

 

 

Figure 17e Subject F5

Figure 17 (cont'd.).

85

famoo‘am é'u-ohalo’on .t’o‘ooodooy

 

44 #4 L

A A_A A A A

ééétéééééeé

 

 

hon (I'll-1
3

 

a do vii do ah ah ii 36 db «6' dB
“"0"", tumuoan)

 

 

Figure 17f Subject F6

Figure 17 (cont'd.).

86

_
fiummm Juahoé'oa fohw

 

"m Hoodoo m (loan)

wool

-HN‘
42004

 

 

 

6 66 1b :5 W do do do 366 460 05
""0"“’ nouwmucav

—

 

 

Figure 18a Subject F1

Figure 18 Rearward Running Muscle Power Curves

87

N
fibmw‘avwea fwhoé‘on Xoheatooy

 

I”!

W out - 22.2401
1321 m Mm) - ~31”
H

mom

ooo+

 

 

 

 

 

Figure 18b Subject F2

Figure 18 (cont'd.).

88

flbmoe‘m é’u-ohoé‘ow 4’0th

nook
“m4 MN.

"m'
IM‘

 

A A A A A A A A

 

 

 

 

 

'Figure 18c Subject F3
Figure 18 (cont'd.).

89

Jamalvw” é‘mhod’ow £4404.th

 

um,

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i-tooo

 

 

 

“"°"’ unrulmm

 

 

Figure 18d Subject F4

Figure 18 (cont'd.).

M

90

fbmw‘oMao é'uohoo‘obn IO‘OQOJO‘D'

 

‘ . ‘ O
A g A

A A A A A A A A A A

3%

ms;

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Figure 18e Subject F5
Figure 18 (cont'd.).

 

91

 

22$:

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l-tooo

 

 

 

fbmoda'woo Jmhoé'ow Xahoofooy
mu. m Goalie.) - amo-
m m fled.) - 43m
6 06o 26o So 066 o6o o6o 76o o6o
‘””“”“’ 1113600)

Figure 18f Subject F6

Figure 18 (cont'd.).

 

St
bu
pt
un
ne
da

mu

anl
de:

901

Im

"dflj'fl'rthrq

thrc

real

92
positive burst from toe strike to approximately 15% of

stance. This was followed by a small amplitude negative
burst until approximately 45% of stance. The third power
phase was a large amplitude positive burst from mid stance
until just prior to heel off when a final small amplitude
negative burst occurred. Following presentation of the EMG
data the power curves will be explained relative to the
muscle action.

Table 8 displays the average peak positive power of
three trials from each subject during the forward running
and rearward running conditions. A paired student t-test
demonstrated no significant differences in peak positive

power between conditions.

 

Table 8
Average peak positive power ~ running
(Watts)
Subject # Forward Rearward Difference
F1 1031 636 395
F2 528 439 89
F3 2050 251 1799
F4 538 354 184
F5 634 439 195
F6 .467 303 164
XD = 471 SD = 658 t = 1.753

Table 9 displays the average peak negative power of
tflxree trials from each subject during the forward and

rearward running conditions. A paired student 't-test

93
demonstrated significantly (p<.05) greater peak negative

values during the forward running conditions.

 

Table 9
Average peak negative power ~ running
(Watts)
Subject # Forward Rearward Difference
F1 ~1225 ~38 ~1187
F2 ~550 ~89 ~461
F3 ~1099 ~513 ~586
F4 ~805 ~132 ~673
F5 ~635 ~165 ~47O
F6 ~588 ~119 ~469
XD = ~641 SD = 280 t = ~5.608

p<.05

Table 10 presents the average positive work of three
trials from each subject during the forward and rearward
running conditions. A paired student t~test demonstrated no

significant differences between conditions.

 

Table 10
Average positive work - running

(Joules)
Subject # Forward Rearward Difference
F1 71 40 31
F2 43 23 20
F3 182 9 173
F4 33 31 2
F5 49 26 23
F6 29 29 0

xD = 42 sD = 66 t = 1.559

94
Table 11 presents the average peak negative work of

three trials during forward and rearward running conditions.
A paired student t~test demonstrated significantly (p<.05)

greater negative work during the forward running condition.

 

Table 11
Average negative work ~ running

(Joules)
Subject # Forward Rearward Difference
F1 ~56 ~1 ~55
F2 ~33 ~4 ~29
F3 ~47 ~33 ~14
F4 ~41 ~9 ~32
F5 ~32 ~8 ~24
F6 ~32 A~7 ~25

XD = '30 SD = 14 t a 5.249

p<.05

The EMG activity from the muscles surrounding the knee
joint are now analyzed for the two running conditions. The
active muscles should be responsible for the knee power
generation and absorption requirements. Figure 19 presents
the firing pattern of each of the six knee muscles studied
during the stance phase of forward running from heel strike
(HS) to toe off (TO). Figure 20 presents the firing pattern
of each of the six knee muscles studied during the stance
phase of rearward running from toe strike (TS) to heel off
(H0). Figures 19 and 20 present the average timing pattern
from all six subjects. For ease of viewing the direction of

travel is from left to right in each of the figures.

Rectus Femoris

Vastus Lateralis

Vastus Medialis

Biceps Femoris

 

Gastrocnemius

Tibialis Anterior

 

_ A i :7 L A L A . A
as 10 20 30 40 so 65 7o 36 56 fo
5 Stance Phase

Figure 19 Forward running EMG pattern

Rectus Femoris

   

Vastus Lateralis

Vastus Medialis

 

Biceps Fmris -Q-cncu-ununnonunngggngp
Gastrocnemius W
Tibialis Anterior —_ —

 

T8: 10 20 30 4b 50 ab io ab db do
\ Stance Phase

Figure 20 Rearward running EMG pattern

96
Table 12 gives the mean muscle on time and standard

deviation (s.d.) across subjects in percentage (%) of stance
phase for each muscle during the forward and rearward
running conditions. A within subject design using a paired

t test with the level of significance is presented for each

 

muscle.
Table 12
Total on time for individual muscles ~ running
- ( % )

Muscle Forward Rearward t~1eve1 p<
Rectus femoris 45 :.16 60‘: 3 ~2.070
Vastus lateralis 48 1’7 65.: 3 ~7.765 .001
Vastus medialis 53‘: 9 71‘: 5 ~6.379 .01
Biceps femoris 55,1 14 77‘: 4 ~4.234 .01
Gastrocnemius 83‘: 11 78‘: 7 O
Tibialis Anterior 50 i.37 58 :_7 .52

EMG data during forward running has considerable
variability in the reported literature (36). The results
presented in Figure 19 are generally consistent with
Nillson's(35) and Komi's(26) data. Comparison of the three
knee extensor muscles (rectus femoris, vastus lateralis, and
vastus medialis) between the forward running and rearward
running conditions yield several consistent results. The
vastus lateralis, vastus medialis, and biceps femoris had
statistically greater (p<.05) total "on time" in the
rearward running condition than in the forward running
condition. The rectus femoris demonstrated a trend toward

increased on time in rearward running but the higher

97
variability in the forward running condition decreased the

power of the statistic. The increased variability may have
been a function of the dual role of the rectus femoris as
both a hip flexor and a knee extensor. Comparing the EMG
data to the moment and power curves suggests that in forward
running the knee extensors acted primarily eccentrically to
absorb the shock of heel strike and then provide a smaller
concentric generation of power at mid stance for propulsion.
This contrasts sharply with rearward running where the knee
extensors acted predominately concentrically as power
generators, with only small eccentric phases.

Though the biceps femoris showed statistically greater
on time in rearward running, the muscle's activity was of a
low level and exemplified by small burst like activity. The
biceps femoris also showed greater periods of inconsistent
activity across subjects.

No statistically significant differences were noted in
gastrocnemius total on time between conditions, but a marked
change in type of muscular contraction and function was
noted. In forward running the gastrocnemius acted
concentrically to propel the limb forward, but in rearward
running it acted eccentrically to absorb the shock of toe
strike.

No statistically significant differences were noted in
tibialis anterior total on time between conditions. The
high variability across subjects in the forward running

condition was primarily the result of two subjects whose

98
firing patterns were only on from the initial O~15 % of

stance. Functionally, the tibialis anterior acted
eccentrically to lower the foot to the floor in forward
running. In contrast to forward running, the tibialis
anterior demonstrated a two stage pattern in rearward
running. The first phase from 20-70 % of stance appeared to
be eccentric in nature which allowed a controlled plantar
flexion of the ankle. The second phase involved a
concentric contraction which functioned to raise the foot
from the floor in the later stance phase. . .
The resultant ground reaction torque is presented in
Figure 21. This was a representative trial from subject F5
comparing forward running (red) to rearward running (green).
The forward running curve was in general agreement with
Holdan and Cavanaugh's(21) finding that the torque was
externally directed during the first 50-60% of stance and
then internally directed during the remainder. The forward
running ground reaction torque in subject F5 suggested
pronation from heel contact to approximately 45% of stance
followed by supination. The rearward running ground
reaction torque was markedly different. In the rearward
running condition the torque began in an inward direction
followed by an outward directed torque. The rearward
running ground reaction torque suggested supination at the
subtalar joint from heel contact to approximately 45% stance
followed by pronation through the remainder of stance. If

Holden and Cavanaugh's assumptions of the ground reaction

HZITIZZ

mmm-qrnzaezzo

99

 

 

 

 

 

 

 

 

 

 

 

38
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13 1 x .' E.
a . E f ( fl 6 1
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_ 1' 't .I “1 K
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4,, “1.1 ‘o "L. h
a “'11.?“ “‘1 "~
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-89 1 1 1 1 I 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1
8.1313 3.135 8.19 8.15 13.313 33.35

FORWARD-RED REHRNRRD'GREEN

Figure 21

Ground reaction torque forward vs rearward running

100
torques relationship to pronation are valid for rearward

running, then it appeared that rearward running prevented

pronation from occurring during the first 45% of stance.

‘VI. CLINICAL IMPLICATIONS

The following chapter presents the application of the
results of this research to three common musculoskeletal
conditions. The three conditions that will be addressed are
patello-femoral dysfunction (PFD), patellar tendinitis, and
anterior cruciate ligament reconstruction. The purpose of
this chapter is to provide a basis for utilizing
retropropulsion in the rehabilitation of patello-femoral
dysfunction and patellar tendinitis and to question the use
of retropropulsion in anterior cruciate rehabilitation.
Estella-femoral dysfunction (BID)

The most common area of pain in runners is the patello-
femoral joint(24). Typically, a runner suffering from PFD
is unable to resume full forward running status for an
extended period. It has been the author's experience that a
runner suffering from patello-femoral dysfunction can
participate in painfree retro-walking and retro-running,
when forward walking and running are symptom producing.

When forms of retropropulsion are incorporated into the
rehabilitaion process, the injured runner returns to forward
running sooner.

The results of this research suggest several possible
contributions to the above observations. The first benefit

of retropropulsion is the longer period of sustained

101

102
quadriceps concentric activity and the decrease in

quadriceps eccentric activity when compared to forward
propulsion. Concentric quadriceps exercises are a standard
tool in patello-femoral rehabilitation. Though no
statistical differences in positive work was found between
conditions, the subjects speed of progression was slower in
the backward conditions, suggesting that at equal speeds
there may have been increased work in the rearward
conditions. Negative work was statistically lower in
backward versus forward propulsion. Negative work can be
performed with less use of a muscle's contractile components
and increased use of the non-contractile components of a
muscle. This suggests from the standpoint of the knee
extensors, retrOpropulsion is primarily a concentric
(contractile component) force generating activity. This
finding substantiates Threlkeld's(45) and Mackie's(29)
findings of increased concentric torque production after a
training program of retro-running.

The clinical observation of painfree retropulsion is
also supported by the following example comparing the
patello-femoral joint reaction force (PFJRF) in forward
running versus rearward running. If the quadricep force
(Fq) and the patellar mechanism angle (B) are known, the
PFJRF can be calculated if we assume the force in the
patellar tendon and the quadriceps to be equal. The moment

arm for the quadriceps mechanism is 4.9 cm based on

103
Smidt's(42) results. Quadriceps force (Fq) can be

calculated using equation (4):

(4) Fq = Knee Moment -100 / 4.9 cm

The patellar mechanism angle (B) is calculated using
equation (5) from Mathews et al.(31), where (a) is the knee

joint angle.

(5) B = 30.46 + 0.53 a

Equation (6) will yield the patello-femoral joint

reaction force.

(6) PFJRF = 2Fq ~sin B/2

Using the peak knee moment during running for subject
F5 the PFJRF is 4808 Newtons in forward running and 2038
Newtons in rearward running. This represents a 58%
reduction in the PFJRF when running backwards in this
subject.

A final possible benefit of retropulsion in the
rehabilitation of patello-femoral dysfunction is the
apparent reduction of tibial internal rotation during
rearward walking, and subtalar joint pronation during
rearward running. If symptoms at the patello-femoral joint

are the result of excessive or poorly timed pronation, then

104
retropropulsion may reduce the symptoms. The faulty lower

extremity mechanics may be the result of weak or poorly
firing muscles. If this is the case, then the marked change
in muscle demands during retropropulsion may serve to
reeducate and strengthen these muscles. This muscle
reeducation could possibly be carried over when ambulating
forwards.
Petellar tendinitis

Patellar tendinitis or "jumper's knee" is common in
athletes involved in running or jumping sports. Curwin and
Stanish(13) report that the eccentric loading phase of
running and jumping is the major etiological factor
contributing to patellar tendinitis. During the
rehabilitative process atrophy and weakening of the muscle-
tendon unit must be avoided while the inflammatory process
subsides. The results of this thesis would support the use
of retropropulsion in the rehabilitation of this condition.
Retropropulsion would decrease the eccentric work which is
involved in forward walking and forward running allowing the
inflammatory process adequate time to subside. The
concentric quadriceps portion of retropropulsion would
decrease atrophy and weakening of the muscle-tendon unit.
Anterior cruciate ligament (ACL)

The literature has reported the use of rearward running
in the rehabilitaion of the ACL reconstructed knee(29).
Based on the EMG findings of.this thesis, retro-running may

in fact be detrimental to healing during the early to middle

105
phase of rehabilitation. This research found an increase in

quadriceps firing time in rearward running, while the
hamstring firing time was inconsistent. This coupled with
the gastrocnemius also firing consistently, may cause a
force couple to cause a rotation which results in an
increased anterior tibial shear in the stance phase of
rearward running. Further research is indicated to support

or refute the use of retropropulsion in ACL rehabilitation.

'VII. CONCLUSIONS

The purpose of this study was to compare the stance
phase of rearward walking and running with the stance phase
of forward walking and running. Based on the findings of
this research the following conclusions are made:

1. Statistically greater peak negative (-) power
occurs at the knee during forward walking and forward
running conditions when compared to their rearward
ambulation counterparts.

2. Statistically greater negative (-) work occurs at
the knee during forward walking and forward running when
compared to their rearward ambulation counterparts.

3. The pattern of EMG activity during walking is
significantly different between forward and rearward
conditions. The rectus femoris, vastus lateralis, vastus
medialis, and tibialis anterior have greater total on time
in rearward walking when compared to forward walking. The
biceps femoris has significantly greater on time in forward
walking when compared to rearward walking.

4. The pattern of EMG activity in running is
significantly different between forward and rearward
conditions. The vastus lateralis, vastus medialis, and
biceps femoris have significantly greater total on time in

rearward running when compared to forward running. The

106

107
biceps femoris activity is inconsistent and at a lower level

in backward running when compared to forward running.

5. The ground reaction torque is markedly different
between the forward and rearward conditions of walking and
running. The direction of the torque suggests a decreased
tibial internal rotation during rearward walking and a
decreased pronation in early-mid stance during rearward
running when compared to their forward ambulation
counterparts.

The stated conclusions have applications in the
training and rehabilitation community. It appears that
retropropulsion may be of benefit in overuse injuries such
as patello-femoral dysfunction and patellar tendinitis. The
use of rearward running may not be benefical during the
early to mid healing phase of anterior cruciate ligament
reconstruction.

Further studies should focus on the hip and the ankle.
Research should also investigate the possiblity of increased

tibial anterior shear during rearward running.

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