THE RELATIONSHIP AMONG HIP ABDUCTOR STRENGTH,
DYNAMIC BALANCE, AND FUNCTIONAL BALANCE ABILITY

A THESIS
Submitted to the Faculty of the School of Graduate Studies
and Research
of
California University of Pennsylvania in partial
fulfillment of the requirements for the degree of
Master of Science

by
Mizue Iwamoto

Research Advisor, Dr. Rebecca Hess
California, Pennsylvania
2009

ii

iii

ACKNOWLEDGEMENTS

I would like to take this opportunity to thank the
many people who played an important role in the completion
of this thesis. First, I thank my advisor Dr. Rebecca Hess
and the members of my committee: Dr. Ben Reuter and Dr.
Chris Harman. Their knowledge, input, and experience were
invaluable to maintain my motivation to think deeper and
work consistently, which lead the success of this product.
I also thank all my classmates, faculty, coaches, and
students at California University of Pennsylvania for their
support and a fun year. To the student-athlete who
participated in my study, I really appreciate your time and
effort.
Finally, I thank my family for always supporting me
and understanding my desire to complete my Master of
Science Degree. I appreciate all the help. I love you all:
Dad, Mom, Natsuki, Ryoma, and my niece, Fua.

iv
TABLE OF CONTENTS

Page
SIGNATURE PAGE

. . . . . . . . . . . . . . . . ii

AKNOWLEDGEMENTS . . . . . . . . . . . . . . . . iii
TABLE OF CONTENTS .

. . . . . . . . . . . . . . iv

LIST OF TABLES

. . . . . . . . . . . . . . . . vii

INTRODUCTION .

. . . . . . . . . . . . . . . . 1

METHODS .

. . . . . . . . . . . . . . . . . . 4

Research Design . . . . . . . . . . . . . . . . 4
Subjects .

. . . . . . . . . . . . . . . . . 5

Preliminary Research . . . . . . . . . . . . . . 5
Instruments .

. . . . . . . . . . . . . . . . 6

Procedures . . . . . . . . . . . . . . . . . . 11
Hypothesis. . . . . . . . . . . . . . . . . . 15
Data Analysis .

. . . . . . . . . . . . . . . 15

RESULTS. . . . . . . . . . . . . . . . . . . . 16
Demographic Data. . . . . . . . . . . . . . . . 16
Hypothesis Testing. . . . . . . . . . . . . . . 17
Additional Findings . . . . . . . . . . . . . . 19
DISCUSSION.

. . . . . . . . . . . . . . . . . 20

Discussion of Results . . . . . . . . . . . . . 20
Conclusion

. . . . . . . . . . . . . . . . . 23

Recommendations

. . . . . . . . . . . . . . . 24

v
REFERENCES. . . . . . . . . . . . . . . . . . . 26
APPENDIX A: Review of Literature .
Balance and measurement tools.

. . . . . . . . 30

. . . . . . . . . 32

Mechanism of balance. . . . . . . . . . . . 32
Movement strategies.

. . . . . . . . . . . . 34

Classification of balance

. . . . . . . . . . 35

Assessment of balance . . . . . . . . . . . . 36
Factors that affect balance . . . . . . . . . . . 38
Proprioceptive deficit.

. . . . . . . . . . . 39

Sport participation . . . . . . . . . . . . . 39
Other factors that affecting balance . . . . . . 41
Balance training . . . . . . . . . . . . . . 42
Role of the hip abductor muscles . . . . . . . . . 43
Hip abductor muscle anatomy.

. . . . . . . . . 43

Gluteus medius function and injury . . . . . . . 44
Summary.

. . . . . . . . . . . . . . . . . . 47

APPENDIX B: The Problem . . . . . . . . . . . . . 49
Statement of the problem . . . . . . . . . . . . 50
Definition of Terms . . . . . . . . . . . . . . 50
Basic Assumptions . . . . . . . . . . . . . . . 52
Limitations of the Study . . . . . . . . . . . . 53
Significance of the Study

. . . . . . . . . . . 53

APPENDIX C: Additional Methods . . . . . . . . . . 55
Informed Consent Form (C1) . . . . . . . . . . . 56

vi
Subject Information Sheet (C2)

. . . . . . . . . 59

Test Score Sheets (C3) . . . . . . . . . . . . . 61
Pictures of each test (C4) . . . . . . . . . . . 64
IRB: California University of Pennsylvania (C5).
REFERENCES

. . 67

. . . . . . . . . . . . . . . . . 73

ABSTRACT. . . . . . . . . . . . . . . . . . . 78

vii
LIST OF TABLES
Table

Title

Page

1

Demographic Data. . . . . . . . . . . . . . . 17

2

Descriptive statistics for ABDTW, LOSW,
and SEBT. . . . . . . . . . . . . . . . . . . 17

3

Correlations among SEBT, LOSW, and ABDTW. . . 19

1

INTRODUCTION

Athletes typically require a high level of balance
ability to perform athletic movements and to decrease risk
of injury.1-4 When any external forces act to alter balance,
athletes move the center of gravity (COG) to control their
body stability.1,3 Thus, an athlete usually has better
balance ability than the non-athletic population.1,2
Moreover, higher competition levels and longer careers have
been shown to positively affect balance ability.3-5
Balance is the single most important element dictating
movement strategies within the closed kinetic chain.1
Vision, vestibular, and somatosensory information is
collected in order to determine the timing, direction, and
amplitude of corrective postural actions.2,4,6,7 These three
systems work together as well as compensate for each
other.2,7,8 According to Guskiewicz et al

1

balance can be

categorized in four different states: static, semidynamic,
dynamic, and functional. Dynamic and functional balance
involve the maintenance of the COG over a moving base of
support which is more critical for athletic movement than
static and semidynamic balance.1,9 There are various factors

2
that affect balance such as proprioceptive deficits, muscle
weakness, and sport participation.2-6 When considering the
relationship between muscle weakness and balance, usually
main focus is hamstring and quadriceps muscles. However,
more proximal muscle structures also have an important role
in maintaining balance.
Gluteus medius is known as a primary hip abductor
muscle and plays a role in stabilizing the pelvis which, in
turn, helps to prevent the Trendelenburg position, or
contralateral hip drop, and ipsilateral genu valgus.10-12 In
other words, weakness of this muscle may cause
inappropriate lower extremity alignment including a valgus
(inward) position of the knee and foot pronation. This
condition may lead more stress on the joint and poor
tracking ability of the patella.13 Therefore, the weakness
of the gluteus medius muscles may increase risk of lower
extremity injuries such as anterior cruciate ligament(ACL)
sprains, iliotibial band friction syndrome, and
patellofemoral pain syndrome.10,12-19
Since hip abductor muscles help to control efficient
lower kinetic movement, use of these muscles is one of the
key components to perform athletic movement effectively.
For this reason, previous researchers recommend to add hip
abductor strengthening exercises to injury prevention

3
program as well as rehabilitation for lower extremity
injuries.12,13,15,16,19 Since hip abductor muscles stabilize the
pelvis and control the lower limb during the gait cycle,
strength and control of these muscles may help to control
balance during athletic activity.13 Moreover, control of the
pelvic motion is critical to maintain total body balance
because weight of the hand, arm, and trunk acts downward
through the pelvis.16 Previous researches have demonstrated
that weakness of the hip abductors alters lower extremity
alignment and it correlated to falls in elderly people as
well as balance ability in individuals with chronic ankle
instability.9,20,21 Since sports utilize complicated
movements, it is critical to clarify the relationship among
hip abductor muscles and specific balance ability such as
dynamic and functional balance. Therefore, the purpose of
this study was to examine the relationship among hip
abductor muscle strength, dynamic balance, and functional
balance ability in collegiate athletes.

4

METHODS

Research Design

This study used a descriptive correlational design.
The variables included the overall limits of stability
(LOS) score as measured by the Biodex Balance System (BBS),
the average of normalized eight directional excursion score
on Star Excursion Balance Test (SEBT), and the hip
abduction strength as measured by the Lafayette Manual
Muscle Test System (MMTS). Based on our preliminary study,
all subjects began with the hip abductor muscle strength
test (ABDT) to reduce local fatigue followed by two balance
tests. The balance tests and strength measurement were
performed on same day. The combination of measurement of
two different balance abilities and specific muscle
strength made this study valuable in addressing the
correlation among dynamic and functional balance, and hip
abductor muscle strength. Findings might be limited to the
specific age group, and National Collegiate Athletic
Association (NCAA) Division II athletes.

5

Subjects

Twenty healthy NCAA Division II athletes, 18 years or
older from California University of Pennsylvania were asked
to participate in this study.

Subjects volunteered to

participate in this study with no coercion from coaches or
faculty after the researcher had explained the purpose.
Prior to any testing, subjects read and signed the
Information Consent Form (Appendix C1) and a Subject
Information Sheet (Appendix C2).

Each subject was assigned

to all three tests on the same day. Any athletes who
suffered from visual, vestibular, balance disorder, severe
lower extremity injury which prohibited them from
participation, and/or a concussion within last six months
was excluded from this study as these conditions may
interfere with accurate balance assessment.

Preliminary Research

Preliminary research was designed to familiarize the
researcher with the LOS test, SEBT, and ABDT, and for a
determination of the time necessary to test each subject.
Procedures for each test was based on manufacturer’s

6
suggestion and previous valid research.22-24 Scoring of the
SEBT using an average distance per leg was considered, as
eight direction of scores (distance in centimeters) are the
functional scores used for analysis.

All of the tests were

conducted on three adult volunteers who are studying or
working at California University of Pennsylvania within the
same age range as the desired population. The pilot
research helped to determine adequate practice times, as
well as appropriate the level of forceplate stiffness for
LOS test. It was determined that the level eight (most
stable) was appropriate for LOS test, and that three
practice trials of SEBT were adequate for subjects to
become familiar with the SEBT and sufficiently minimize
learning effects.

Instruments

The instruments used in this study were a Subject
Information Sheet (Appendix C2), the BBS, the SEBT, the
MMTS, and test score sheets (Appendix C3).

Biodex Balance System (BBS)
The overall LOS score and time to complete the test
can be measured by the BBS(Appendix C4). The LOS test

7
measured by BBS examines dynamic balance ability by
challenging the subjects to move and control their center
of gravity (COG) within their base of support.23-25 LOS is
defined as the outermost range of an area in space that a
person can lean from the vertical position in any direction
without changing his or her base of support.26 During the
test trial, the subjects had to shift their weight on a
moveable platform to move the cursor displayed on an eyelevel screen from the center target to a blinking target,
and back as quickly and with as little deviation as
possible.24,27 The platform tilts a maximum of 20°(from
horizontal plane) in all directions.24,26,27 The BBS offers
eight different levels of difficulty by changing the amount
of stiffness in the platform: L1 is the least stable and L8
is the most stable. The test protocol can be set up for a
bilateral or unilateral stance and includes a grid on the
foot platform to record the foot position for re-testing.25
However, the LOS test using the unilateral stance protocol
is a challenging task even at the least difficult level for
a healthy athletic population.28 Thus, bilateral stance was
used in this study. Ishizuka8 used two practice trials
before the test trial, but suggested that the practice
trials should be four to minimize learning effect.
Therefore, four practice trials were performed in this

8
study. The LOS test score can be represented by the overall
LOS score and time to complete the test. In this study,
only the overall LOS score was used and was recorded on the
Test Score Sheet (Appendix C3). To calculate the overall
LOS score, the following formula was used.24

LOS score % = Straight line distance to target × 100
Actual distance traveled
Overall LOS score = (LOS scores)/8

Scores range from zero to 100 in which a higher score
indicates better control of the COG within the LOS.
Intraclass correlation coefficients (ICCs) for the LOS test
have ranged from .77 to .89.24

Star Excursion Balance Test (SEBT)
The SEBT is a functional test of dynamic balance that
has high intratester and intertester reliability while
challenging an individual’s LOS on solid ground.22 The SEBT
uses a star on the floor with eight lines extending at
45°increments from the center of the grid(Appendix C4)22,29
The line was measured and marked every 1cm from the center
of the grid for all eight directions for the measurement of
the excursion distance.22,29 The eight lines were named
anterolateral (AL), anterior (A), anteromedial (AM), medial

9
(M), posteromedial (PM), posterior (P), posterolateral
(PL), and lateral (L), according to the direction of
excursion in relation to the stance leg; thus the labeling
of the grid was different for the right and left legs.22
During three test trials, the distance between center of
the grid and the point the subject’s leg touched was
recorded, according to suggested test protocols.22 The total
mean score of three tests indicated the mean score of each
excursion. Total mean score of each leg was calculated by
adding all eight mean scores of each excursion. For
experimental or clinical purposes, excursion distances were
normalized to leg length to allow for a more accurate
comparison of performance among participants.29 Means for
the three test trials in each leg calculated for each of
the eight excursions. Then, the mean of the three test
trials were divided by a subject’s leg length to normalize
the score.29 ICCs for intratester reliability ranged from
.78-96.22 Higher scores in centimeters indicated better
balance.

The Lafayette Manual Muscle Test System (MMTS)
The Lafayette Manual Muscle Test System (MMTS) is a
portable device that can be used to obtain more discrete,
objective measures of strength during manual muscle testing

10
(MMT) than can be achieved via traditional MMT(Appendix
C4).19 Although most of the research has involved the use of
the same type of hand-held dynamometer with elderly or
physically impaired populations, the reliability of the
device has been high.11,16 Intratester reliability for hip
abduction particularly has been reported at .932 to .984
for the elderly population, and .92 to .97 for healthy
young adults.23,30 MMTS provides muscle peak force in kg or
lb. Peak force was recorded for each trial and the
following formula was used to calculate normative
strength.31 Distance was defined as between force
application at the level of the femoral condyle and the
pivot point which was the hip joint in this study. The
distance was measured as the distance from the greater
trochanter to the lateral knee joint line of the leg.32
Higher peak force values indicate more strength.

Newtons conversion: 1kg = 9.81N
Torque = (Force in Newtons) x (distance in meter)
Strength = Torque / Body weight in kilograms

11
Procedures

The study was approved by the California University of
Pennsylvania Institutional Review Board (IRB) (Appendix
C5). Prior to the study, the researcher had a meeting with
all potential subjects to explain the concept of the study
and offer the Informed Consent Form (Appendix C1) so that
each subject understood the requirement and risks of
involvement in the study. Qualifications for the subjects
(mentioned in the subject section), requirements, testing
date, and approximate time frame for entire study, one hour,
were also announced.
Before the tests, qualifications for the subjects were
presented again. Once understanding and approving, subjects
signed the Informed Consent Form (Appendix C1) and
completed the Subject Information Sheet (Appendix C2).
Tests were given in the described random order, but with
the MMT being tested first. Prior to beginning each test,
the researcher explained the test procedure and method.

Hip abductor muscle strength test (ABDT)
Procedures for measuring isometric muscle strength of
hip abductor muscles was base on those described by
Andrews.23 The distance between the greater trochanter and

12
lateral knee joint line was measured in meters.32 For test
trials, the isometric “make” test was used rather than
“break” test to obtain a more reliable measurement.33 The
subjects were asked lie supine on the treatment table.
During the “make” test, the researcher was holding the MMTS
perpendicular to the thigh at the lateral femoral
epicondyle while the athlete built force gradually to a
maximum voluntary effort for two seconds.23,32 Then the
subject was asked to maintain maximum effort for five
additional seconds.23,32 The restraints was used to stabilize
the subject’s hips in neutral position. To prevent
alterations in muscle recruitment and compensation during
testing, the subjects were also instructed to keep their
toes pointed towards the ceiling and not to bend their
knees. Subjects were given two practice trials to
familiarize this procedure as well as the feel of pushing
against the MMTS.23 One minute of the recovery time was
provided between each test, and the test was taken a total
of three times for each limb. These tests were then
averaged and recorded into the test score sheet (Appendix
C3).

13
Limits of Stability test (LOS test)
The researcher set up the BBS and computed the
information including subject’s height, weight, and
platform firmness using the bilateral stance. The bilateral
stance balance test was performed with the LOS test and the
platform firmness was set at level eight which was used in
previous study and determined during preliminary study.8 The
subjects were asked to stand on the BBS platform on both
feet and maintain their balance while chasing the cursor.
During the trial, subjects had to move the platform while
chasing the blinking targets which were appeared randomly
on the BBS computer screen. Four practice sessions were
provided before one test trial as recommended by previous
literature.8,25 After each trial, the LOS score was recorded
on the test score sheet (Appendix C3).

Star Excursion Balance Test (SEBT)
Procedures for measuring functional balance ability
was base on those described by Hertel.22 Each subject’s leg
length was measured bilaterally in centimeters as the
distance between the anterior superior iliac crests and the
medial malleolus.29 The subject stood on one leg while
placing the heel on the center of the star. The subjects
were also instructed to hold their hands on their hip, and

14
asked to reach the opposite leg to make a light toe touch
along the chosen line. The subject then returned the
reaching leg back to the center, while maintaining singleleg stance with the other leg. The subject was allowed to
move their torso or lean during this test. The reached
distance was marked along the line and the researcher
measured the distance in centimeters from the center of the
grid to the mark with a tape measure. The test needed to be
repeated if the reach foot was used to provide support when
touching the ground, if the subject lifted the stance foot
from the center of the grid, or if the subject lost his or
her equilibrium at any point in the trial.22
Previous researcher22 suggested performing six practice
trials in order to minimize learning effect. However, our
preliminary study showed that three practice trials would
be adequate. Thus, the subject performed three bouts of
practice trials followed by three test trials in each of
the eight directions to minimize learning effect.
Half of the subjects began all bouts by performing the
right-stance-leg tests first, and the other half of the
subjects began by first performing the left-stance-leg
tests. The subjects had 15s of resting time between each
trial. The order of testing for all subjects was AL, A, AM,
M, PM, P, PL, and L. When the subject was reaching in the

15
lateral and posterolateral line, one had to reach behind
the stance leg to complete the task. After performing all
excursions on the initial stance leg, the same protocol was
repeated with the contralateral leg serving as the stance
leg. The mean for the three test trials in each leg was
calculated for each of the eight excursions. Then, the mean
of the three test trials were divided by a subject’s leg
length to normalize the score.29

Hypothesis

The following hypothesis was tested in this study:
There will be a positive correlation among SEBT, LOS, and
ABDT peak force scores, for functional balance, dynamic
balance, and hip abductor muscle strength.

Data Analysis

A Pearson Product Moment Correlation coefficient was
used to determine the relationship among balance (LOSW and
SEBT) and hip abductor muscle strength (ABDTW). The data
analysis was performed using the SPSS 16.0 statistical
software package at an alpha level of ≤ 0.05.

16

RESULTS

The purpose of the study was to examine the
relationship among hip abductor muscle strength, dynamic
balance, and functional balance ability in healthy
athletes. Subjects were tested by using the ABDT, the LOS,
and the SEBT. The ABDT was used to measure subjects’ hip
abductor muscle strength, and the LOS and SEBT were used to
measure dynamic balance and functional balance
respectively.

Demographic Data

A total of 20 subjects (11 males, 9 females) completed
this study. All of the subjects were volunteers and were
physically active individuals, participating in NCAA
Division II football (n = 9), soccer (n = 1), track (n =
2), or swimming team (n = 8) at California University of
Pennsylvania. Demographic data (Table 1) were collected by
the researcher at the beginning of the study.

17
Table 1. Demographic Data
Male (N = 11)
Age
Height
Weight
Female (N = 9)
Age
Height
Weight

Minimum
(yrs) 19
(cm)
172.7
(kg)
74.8

Maximum
22
195.6
108.9

Mean
20.55
182.19
88.45

SD
1.13
6.44
13.12

(yrs) 18
(cm)
157.5
(kg)
53.5

23
179.0
81.6

20.33
165.61
64.20

1.73
6.35
8.47

Hypothesis Testing

Hypothesis testing was performed by using data from
the 20 subjects who completed all tests at an alpha level
of ≤ 0.05. Descriptive statistics for the SEBT, LOSW, and
ABDTW are shown in Table 2.

Table 2. Descriptive statistics for
Minimum
Maximum
SEBT
.84
1.15
LOSW
.13
.86
ABDTW
.94
2.04

ABDTW, LOSW, and SEBT
Mean
SD
.9520
.08286
.4221
.20809
1.4561
.28620

Hypothesis: There will be a positive correlation among
SEBT, LOS, and ABDT scores, for functional balance, dynamic
balance, and hip abductor muscle strength. A Pearson
Product Moment Correlation coefficient was calculated to
examine the linear relationship among all three variables.

18
Prior to calculating the correlation for the three
variables, the following two additional analyses were
performed.

If appropriate, each variable was reduced to

one total score using either average right and left limb,
and/or normalized test scores.
Dependent t-tests were performed between right and
left limb scores for ABDT and SEBT. Because no significant
differences were identified between limb for ABDT (t = 1.259, P = .223), or SEBT score (t = 1.073, P = .297), data
from the right and left limb trials were averaged and
analyzed as one variable for the main hypothesis.
A Pearson Moment Correlation coefficient as calculated
for the averaged scores of SEBT, LOS, ABDT, height, and
weight and indicated that weight, was significantly
correlated to ABDT and LOS scores. (r = .740, P < .001, r =
-.772, P < .001) Therefore, ABDT and LOS scores were
divided by body weight to normalize the data, and analyzed
as one variable for the main hypothesis (ABDTW and LOSW
respectively).
Conclusion: A significant moderate correlation between
hip abductor muscle strength (normalized ABDTW) and
functional balance (SEBT) ability was present (r = .514, P
= .021). However, there were no significant correlation
between functional balance (SEBT) and dynamic balance

19
(normalized LOSW), or between dynamic balance and hip
abductor muscle strength(Table 3).

Table 3. Correlations among SEBT, LOSW, and ABDTW
SEBT
LOSW
ABDTW
Pearson Correlation
1.000
.382
.514*
Sig. (2-tailed)
.097
.021
LOSW
Pearson Correlation
.382
1.000
-.037
Sig. (2-tailed)
.097
.878
ABDTW
Pearson Correlation
.514*
-.037
1.000
Sig. (2-tailed)
.021
.878
*. Correlation is significant at the 0.05 level (2-tailed)
SEBT

Additional Findings

An additional Pearson Product Moment correlation was
performed to examine the relationship among SEBT, LOSW,
ABDTW, and gender. A significant correlation between gender
and LOSW (r = .690, P = .001) was recorded, and further
analyzed for gender by LOSW using a one way ANOVA as LOS is
correlated to weight.

However, a significant difference

was found between males and females (F = 16.352, P = .001),
whereby females scored significantly better LOS scores even
when normalized by weight.

20

DISCUSSION

Discussion of Results

The main finding was that hip abductor muscle strength
was positively moderately correlated to functional balance
ability as measured by a standing reach test (the SEBT).
This finding between hip abductor strength and functional
balance extends and is consistent with findings of previous
studies.20,21 Trudelle-Jackson et al20 reported differences
between healthy old women who had a history of falling
within one year and who had no history of fall. They
reported that weakness of the hip abductor strength was one
of the predictive factors in subjects who had a history of
falling. However, the history of falls was self-reported
and did not provide objective data about balance ability.
Hubbard et al21 examined various correlations among
multiple measures of functional and mechanical instability
30 young adults (15 males and 15 females with an average
age of 20.3 years old) who had chronic ankle instability.
The activity level of the subjects was not stated. Hubbard
reported that hip abduction and hip extension strength
positively correlated with SEBT. In other words, again,

21
increased hip abductor strength correlated with functional
balance.

Interestingly, while there was significant

correlation between hip abductor strength and functional
balance, dynamic balance did not correlate to hip abductor
strength which we did not expect. This different correlation
may be due to the use of different types of movement
strategy during the tests. As well, when the hip abductors,
particularly gluteus medius is strong, the stance leg
during a one-legged reach will be more stable and not
result in a “dropped” hip (the Trendelenberg sign). In
other words, maintaining correct lower extremity alignment
during single leg stance may minimize the unnecessary
stress at the knee and the ankle by preventing excessive
knee adduction or foot pronation, which in turn, helps
other kinetic chain structures to work efficiently.
Balance is achieved through a compilation of sensory,
motor, and biomechanical processes.1,3,5,9 Muscle coordination
and sensory organization are two important components of
the central nervous system (CNS) which serve to maintain
upright position. Three different movement strategies are
used to prevent oneself from falling.25 The most effective
and common strategy is the ankle strategy that is used when
small postural sway adjustment is needed.1,16 However, if
the COG is near to the LOS perimeter, a hip strategy is

22
used to prevent the ankle from excessive movement that
involves the large and rapid motions at the hip.1 The ankle
strategy may be used during the LOS test because it
challenged the subjects to move and control their COG on
the movable platform without changing the base of support
which required minimum joint movement. However, SEBT is a
more challenging dynamic task than LOS test. Subjects were
required to move their torso during SEBT to reach as far as
they could while maintaining their balance; this task
involved larger joint movement than the dynamic balance
(LOS) test. Thus, during a standing reach test (the SEBT),
subjects may have used the hip strategy rather than ankle.
Previous findings34 also imply that an ankle strategy
is used during dynamic balance tasks. Croft et al34 examined
the joint angles and muscle activity during static and
dynamic balance tasks using EMG and force plate data.
Subjects stood on the three different surfaces (solid, foam,
and air-filled disc) and performed single leg balance.
Although they used single leg stance and different device
to examine the relationship between balance ability and
particular muscles, their dynamic balance test protocol was
similar to our LOS test; standing on the movable base but
the subjects do not require large joint movement to
maintain their balance. The authors reported EMG activity

23
of the gastrocnemius and peroneus longus relative to center
of pressure (COP) displacement, but did not identify the
correlation between gluteus medius activity and COP
displacement. As a result, their subjects may have used the
muscles surrounding their ankle rather than their proximal
muscles, such as gluteus medius, to complete their dynamic
balance task. This finding supports the notion that our
subjects used an ankle strategy for balance during the LOS
test rather than hip.
We did not find a significant correlation between
dynamic and functional balance ability that has been
reported in a previous study.35 Nakagawa and Hoffman35
evaluated individuals with recurrent ankle sprains for
static, dynamic balance, and the SEBT. However, only a very
weak correlation among SEBT score, static balance, and
dynamic balance ability was reported. These results,
particularly combined with our findings, suggest that each
test might measure different aspects of neuromuscular
control.

Conclusions

Functional balance and hip abductor muscle strength
appears to be moderately related in healthy Division II

24
collegiate athletes. However, there was no significant
correlation between hip abductor muscle strength and
dynamic balance, and between functional balance and dynamic
balance ability indicating that these tests require
different neuromuscular control. Additionally, body weight
appears to correspond to dynamic balance and hip abductor
muscle strength, which may result in a heavier athlete
scoring poorer dynamic balance and higher muscle strength
unless the data is normalized.

Recommendations

Our findings suggest that weakness of the hip abductor
muscle may lead poor performance on functional balance
tasks that involve reaching with one leg while standing on
the other. As previous researchers reported, weak hip
abductor may cause inappropriate lower extremity alignment
which may increase the risk of injury.10-19 Therefore,
strengthening the hip abductor muscles may not only improve
functional balance, but also reduce the risk of injury. As
there are limited studies available that have assessed the
relationship among these three variables, further research
is needed in this area.

Moreover, as body weight appears

to be significantly correlated to dynamic balance as well

25
as hip abductor muscle strength, any dynamic balance
ability that is measured using the Biodex Balance System
(BBS) for LOS, as well as muscle strength measured by a
hand-held dynamometer should be normalized by body weight
when comparing scores among athletes.

26
REFERENCES
1.

Guskiewicz
KM.
Regaining
postural
stability
and
balance.
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Prentice
WE,
ed.
Rehabilitation
Techniques for Sports Medicine and Athletic Training.
New York, NY: McGraw-Hill Companies, Inc;2004:156-185.

2.

Perrin P, Deviterne D, Hugel F, Perrot C. Judo, better
than
dance,
develops
sensorimotor
adaptabilities
involved in balance control. Gait Posture. 2002;15:187194.

3.

Hahn T, Foldspang A, Vestergaard E, Ingemann-Hansen T.
One-leg standing balance and sports activity. J Med Sci
Sports. 1999;9:15-18.

4.

Paillard T, Noe F. Effect of expertise and visual
contribution on postural control in soccer. J Med Sci
Sports. 2006;16:345-348

5.

Paillard T, Noe F, Riviere T, Marion V, Montoya R,
Dupui P. Postural performance and strategy in the
unipedal stance of soccer players at different levels
of competition. J Athl Train. 2006;41:172-176.

6.

Matsuda S, Demura S, Uchiyama M. Center of pressure
sway characteristics during static one-legged stance of
athletes
from
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sports.
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Sport
Sci.
2008;26:775-779.

7.

Nashner LM, Black FO, Wall C. Adaptation to altered
support and visual conditions during stance: patients
with vestibular deficits. J Neurosci. 1982;2:536-544

8.

Ishizuka T. Recovery time on limits of stability from
functional fatigue in Division II collegiate athletes
[master’s
thesis].
California,
PA:
California
University of Pennsylvania;2007.

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Blackburn T, Guskiewicz KM, Petschauer MA, Prentice WE.
Balance and joint stability: the relative contributions
of proprioception and muscular strength. J Sport
Rehabil. 2000;9:315-328.

10.

Russell KA, Palmieri RM, Zinder SM, Ingersoll CD. Sex
differences in valgus knee angle during a single-leg
drop jump. J Athl Train. 2006;41:166-171.

27

11.

Hollman JH, Kolbeck KE, Hitchcock JL, Koverman JW,
Krause DA. Correlations between hip strength and static
foot and knee posture. J Sport Rehabil. 2006;15:12-23.

12.

Earl JE. Gluteus medius activity during 3 variations of
isometric
single-leg
stance.
J
Sport
Rehabil.
2004;13:1-11.

13.

Lorenz D. Targeting the hips to help prevent anterior
knee
pain.
Strength
and
Conditioning
Journal.
2006;28:32-37.

14.

Claiborne TL, Armstrong CW, Gandhi V, Pincivero DM.
Relationship between hip and knee strength and knee
valgus during a single leg squat. Journal of Applied
Biomechanics. 2006;22:41-50.

15.

Carcia C, Eggen J, Shultz S. Hip-abductor fatigue,
frontal-plane landing angle, and excursion during a
drop
jump. J Sport Rehabil. 2005;14:321-331.

16.

Friel K, McLean N, Myers C, Caceres M. Ipsilateral hip
abductor weakness after inversion ankle sprain. J Athl
Train. 2006;41:74-78.

17.

Niemuth PE, Johnson RJ, Myers MJ, Thieman TJ. Hip
muscle weakness and overuse injuries in recreational
runners. Clin J Sport Med. 2005;15:14-21.

18.

Fredericson M, Cookingham CL,Chaudhari AM, Dowdell BC,
Oestreicher N, Sahrmann SA. Hip abductor weakness in
distance runners with iliotibial band syndrome. Clin J
Sport Med. 2000;10:169-175.

19.

Heinert BL, Kernozek TW, Greany JF, Fater DC. Hip
abductor weakness and lower extremity kinematics during
running. J Sport Rehabil. 2088;17:243-256.

20.

Trudelle-Jackson EJ, Jackson AW, Morrow JR. Muscle
strength and postural stability in healthy, older
women: implications for fall prevention. Journal of
Physical Activity and Health. 2006;3:292-303.

21.

Hubbard
TJ,
Kramer
LC,
Denegar
CR,
Hertel
J.
Correlations among multiple measures of functional and
mechanical instability in subjects with chronic ankle

28

22.

instability. J Athl Train. 2007;42:361-366.
Hertel J, Miller J, Denegar CR. Intratester and
intertester reliability during the star excursion
balance tests. J Sport Rehabil. 2000;9:104-116.

23.

Andrews AW, Thomas MW, Bohannon RW. Normative values
for isometric muscle force measurements obtained with
hand-held dynamometers. Phys Ther. 1996;76:248-259.

24.

Biodex Balance
System; 1999.

25.

Hinman MR. Factors affecting reliability of the Biodex
Balance System: a summary of four studies. Sport
Rehabil. 2000;9:240-252.

26.

Raty HP, Impivaara O, Karppi SL. Dynamic balance in
former elite male athletes and in community control
subjects. J Med Sci Sports. 2002;12:111-116.

27.

Yaggie J, Armstrong
fatigue on indices
2004;13:312-322.

28.

Perron M, Hebert LJ, McFadyen BJ, Belzile S, Regniere M.
The ability of the Biodex Stability System to
distinguish level of function in subjects with a
second-degree ankle sprain. Clinical Rehabilitation.
2007;21:73-81.

29.

Gribble PA, Hertel J. Considerations for normalizing
measures
of
the
star
excursion
balance
test.
Measurement in physical education and exercise science.
2003;7:89-100.

30.

Kelln BM, McKeon PO, Gontkof LM, Hertel J. Hand-held
dynamometry: reliability of lower extremity muscle
testing in healthy, physically active, young adults. J
Sport Rehabil. 2008;17:160-170.

31.

The Lafayette Manual Muscle Test System user’s manual.
Lafayette, IN: Lafayette Instrument. 2003.

32.

Mercer VS, Lewis Cl. Hip abductor and knee extensor
muscle strength of children with and without down
syndrome. Pediatr Phys Ther. 2001;13:18-26.

System.

Shirley,

NY:

Biodex

Medical

WJ. Effects of lower extremity
of balance. J Sport Rehabil.

29
33.

Stratford PW, Balsor BE. A comparison of make and break
tests using a hand-held dynamometer and the Kin-Com.
JOSPT. 1994;19:28-32.

34.

Croft
JL,
Tscharner
VV,
Zernlcke
RF.
Movement
variability and muscle activity relative to center of
pressure during unipedal stance on solid and compliant
surfaces. Motor Control. 2008;12:283-295

35.

Nakagawa L, Hoffman M. Performance in static, dynamic,
and clinical tests of postural control in individuals
with
recurrent
ankle
sprains.
J
Sport
Rehabil.
2004;13:255-268

30

APPENDIX A
Review of Literature

31
Balance is the single most important element dictating
movement strategies within the closed kinetic chain.1 Also
it is the single most important component of athletic
ability because of its implicit involvement in nearly all
forms of movement.2,3 As Trendelengburg’s test indicates, the
gluteus medius muscle plays a great role in maintaining
pelvic alignment in a single-leg stance.4 The gluteus medius
provides hip abduction movement as well as external
rotation of the femur.4,5 The weakness of the hip abductor
muscle may cause Trendelengburg position and inappropriate
lower extremity alignment which potentially increase risk
of injury.4,6 Therefore, strengthening this muscle group may
help to decrease lower extremity injuries including overuse
injuries and knee sprains.4,7-9 From this fact, it is not
difficult to associate static balance and gluteus medius
strength. Moreover, it has been found that there is
significant correlation between hip abductor weakness and
experience of fall in healthy old women as well as balance
ability in the individuals who has chronic ankle
instability.10,11 However, since sports utilize more
complicated movements, it is critical to clarify the
relationship between hip abductor strength and specific
balance ability such as dynamic and functional balance.
Thus, the purpose of this review of literature is to

32
discuss the relationship among hip abductor muscle strength,
dynamic balance, and functional balance. The topics that
will be discussed include the balance and measurement tools,
factors that affect balance, and role of the hip abductor
muscle.

Balance and Measurement Tools

Balance is the single most important element dictating
movement strategies within the closed kinetic chain.1
Therefore, balance ability is necessary for our general
life activity as well as for athletic performance.2,3 The
term “postural equilibrium” is more commonly used for
balance. However, while postural equilibrium is used as a
broader term, balance is specifically defined as ability to
maintain the body’s center of gravity (COG) within the base
of support provided by the feet.1,2,12

Mechanisms of Balance
Balance is achieved through a compilation of sensory,
motor, and biomechanical process and maintain balance is a
function of a number of sensory inputs to the central
nervous system (CNS).2,14,15 Muscle coordination and sensory
organization are the two important components of the CNS to

33
maintain upright position. Muscle coordination determining
the temporal sequencing and distributing muscle contraction
of the legs and trunk that promote maintaining balance,
whereas sensory organization involves information from
visual, vestibular, and somatosensory systems and it
coordinates postural control.2,14,16 Vision measures the
orientation of the eyes and head in relation to surrounding
objects. Vestibular information is collected from the inner
ear which measure gravitational, linear, and angular
accelerations of the head in relation to inertial space.
This sense has a minor role in the maintenance of balance
when the other two senses are providing accurate
information.1,13,17
Somatosensation or proprioception is defined as
specialized variation of the sensory modality of touch that
recognize the sensation of joint movement and joint
position.1,2,18 Since this sense provides the CNS with
information related to movement and posture, it works
closely with balance. Muscle spindles, Golgi tendon organs,
and joint receptors are included for the proprioceptors.
While muscle spindles provide information about the
relative muscle length, Golgi tendon organs work as safety
devices by recognizing the tension developed by muscle. The
joint receptors provide sensation about the orientation of

34
body parts as well as feedback about the rates of limb
movement.1 If any component of the visual, vestibular,
and/or somatosensory sense disrupted, balance may be
impaired.14 At the same time, these three systems work
together as well as compensate for each other.1-3

Movement Strategies
People use a variety of different balance strategies
when asked to perform balance tasks. To prevent oneself
from falling, the body must control the COG within safer
limits of stability (LOS), which is defined as the
outermost range of an area in space that a person can lean
from the vertical position in any direction without
changing his or her base of support.12 Afferent sensory
information from the ankle, knee, and hip joints have
responsible to initiate the postural control through the
three different movement strategies.1 All strategies, ankle,
hip, and stepping strategy, focus movement to one primary
joint complex.
Ankle strategy is used when small postural sway
adjustment is needed by rotating the body as a rigid mass
about the ankle joint.1,20 This is the most effective and
common strategy to be selected when there is any type of
somatosensory problem and when COG is within the LOS.1,14 If

35
excessive displacement of COG occurs and the ankle is
unable to control the sway, hip strategy is initiated.20 The
hip strategy helps to prevent the ankle from excessive
movement to prevent further harm by initiating the large
and rapid motions at the hip joints. This strategy is most
effective when COG is near to LOS perimeter or when
boundary of the LOS is narrow.1 Since musculoskeletal
abnormality can reduce range of motion of the joint, ankle
sprain and knee sprain shrink the LOS and increase the risk
for a fall.1,21 Whenever the COG is the outside of LOS, a
step or stumble is the only choice for the person which is
named the stepping strategy.17,22

Classification of Balance
Commonly balance is categorized as static and dynamic
because balance has both static and dynamic processes.1,3
However, since an athlete typically performs more
complicated movements, to be more clinically accurate
Guskiewicz et al1 states that balance should be categorized
in four different states: static, semidynamic, dynamic, and
functional balance. Static balance is referred as the
ability to maintain the COG within a fixed, stable base of
support such as single-leg stance on a level floor, whereas
semidynamic balance is either the ability to maintain the

36
COG over a fixed support while standing on a moving surface
or unstable surface such as the biomechanical ankle
platform system (BAPS) board.1,2 Dynamic balance involves
the maintenance of the COG within the LOS over a moving
base of support.1,2 Functional balance is similar to dynamic
balance with the inclusion of sport-specific tasks such as
throwing and catching.1,2

Assessment of Balance
There are several ways to measure balance including
the Biodex Balance System (BBS), Romberg test, Star
Excursion Balance Test (SEBT), and Balance Error Scoring
System (BESS).1,12,23-26 The Romberg test is one of the
traditional methods used to assess static balance. However,
in a clinical setting, it has been criticized due to lack
of sensitivity and objectivity.27 The BESS is another
subjective assessment tool which is recommended over the
Romberg test.1,26 The subject performs the test without
visual information in three different leg stances on the
two different surface. The performance is scored by adding
one error point such as hands lifted off iliac crests. BESS
is known as a reliable test but only for static balance
ability.

37
SEBT is a functional test of dynamic balance that has
high intratester and intertester reliability while
challenging an individual’s LOS.23 The SEBT uses a star on
the floor with eight lines extending at 45°increments from
the center of the grid.24 The line is marked by 5cm from the
center of the grid for all eight directions for the
measurement of the excursion distance.24 The eight lines
outline the anterolateral (AL), anterior (A), anteromedial
(AM), medial (M), posteromedial (PM), posterior (P),
posterolateral (PL), and lateral (L), according to the
direction of excursion in relation to the stance leg; thus
the labeling of the grid will be different for the right
and left legs.23 For experimental or clinical purposes,
excursion distances are normalized to leg length to allow
for a more accurate comparison of performance among
participants.24 Each excursion distance is divided by a
participant’s leg length, and then multiplied by 100 to
normalize the score.24

ICCs for intratester reliability

range from .78-96.23
The BBS can be used to measure individual’s LOS which
examines dynamic balance ability by challenging the
subjects to move and control their center of gravity (COG)
within their base of support.28 During the test trial, the
subjects must shift their weight to move the cursor from

38
the center target to a blinking target, which is displayed
on BBS computer screen, and back as quickly and with as
little deviation as possible.28 The platform is moveable and
tilts a maximum of 20°(from horizontal plane) in all
directions.12 The BBS offers eight different levels by
changing the amount of stiffness in the platform: L1 is the
least stable and L8 is the most stable. The test protocol
can be set up for either bilateral or unilateral stance and
includes a grid on the foot platform to record the foot
position.12 However, the LOS test with unilateral stance
protocol is a challenging task even at the least difficult
level for a healthy athletic population.25 Intraclass
correlation coefficients (ICCs) for the LOS study ranged
from .77 to .89.12

Factors that Affect Balance

As mentioned in the previous section, balance is
maintained by many structures including the CNS. From a
clinical perspective, separating the sensory and motor
processes of balance means that a person may have impaired
balance due to one or both of the following: (1) the
position of the COG relative to the base of support is not
accurately sensed by visual, vestibular, and/or

39
somatosensory input, and or (2) the automatic movements
required to bring the COG to a balance position are not
timely or effectively coordinated. Thus, balance deficits
can be related to sensory or motor issues.1,17

Proprioceptive Deficit
Related to COG, one study demonstrated that muscular
weakness, proprioceptive deficits, and range of motion
(ROM) deficits may cause the athlete to lose their balance
because it challenge a person’s ability to maintain their
COG within the body’s base of support.1 For example, when an
athlete has a lateral ankle sprain, joint proprioceptors
are believed to be damaged. This damage may cause joint
deafferentation, and leads to diminished supply of messages
from the injured joint via afferent pathway.1 Since the
stability of the ankle joint is paramount when considering
regulation of balance, this disruption of proprioceptive
function would greatly affect on balance ability,
especially with dynamic balance.2,29

Sports Participation
Sports participation enhances the ability to use
somatosencory and otolithic information.3,13,14,18,26,30-32 Thus,
an athlete usually has better balance ability than the non-

40
athletic population.3,18 Several studies have been performed
on different group of athletes but the balance ability
differences between sports participation has been different
depending on researchers.3,13,14,26,30 In any sports, the
vestibular, visual, and/or somatosensory are increased in
some way. Perrin18 compared static and dynamic balance among
high-level judoists, professional dancers, and controls.
Controls are defined as women and men in similar age who
are not held a sports license nor practiced leisure
physical activities at a level liable to modify their
postural control. While judoists and dancers had superior
balance ability than control subjects with eyes open, only
judoists retained a significantly better stance with eyes
closed. This result indicates that vision is essential
component to maintain balance for dancers whereas Judo
training leads the best abilities in all balance
circumstances. Other than type of sports, the participation
level and the length of career are also related to their
balance ability.13,14,31 In a study examining soccer and
basketball players, the longer the career in the sport
and/or higher competition level they participate, the
better the balance ability.13,14,31

41
Other Factors That Affect Balance
One of the factors that cannot be eliminated is age.
Several studies have demonstrated that dynamic balance is
greatly related to age; an older population has decreased
dynamic balance.32 As people get older, their joint ROM as
well as strength level usually decreases. While decreased
joint ROM reduces individual’s LOS, muscle weakness itself
could decrease balance ability.1 More importantly, these
factors lead to a change in their movement strategies.
While a young population typically uses the ankle strategy,
older populations as well as the injured athletes more
commonly use the hip strategy that controls the balance
with large movement at the hip.33
Fatigue from exercise also negatively affects
balance.29,34-36 While the most effective movement strategy is
the ankle strategy, people change their postural control
strategy in fatigued situation.35 The main muscles to
control balance in ankle strategy are the anterior tibialis
and calf muscle and they control small sway.1 However, when
these muscles are fatigued, the efficiency of muscle
contraction reduces, and coordination of the sway is
decreased. One study suggested that it would take 10
minutes to recover from fatigue.34 However, during this time

42
period, the athletes’ postural sway will increase because
they potentially return to the ankle strategy.34,35

Balance Training
Balance exercise programs have been performed
particularly for decreasing injury rates. Although
Soderman37 concludes that there were no positive or negative
effect of balance training on injury prevention, several
other studies have shown positive results.2,21,38,39 Because
poor balance ability is not the only factor that causes
injury, it is not easy to say if balance training itself
effects injury prevention. However, a numbers of studies,
utilizing various methods and various athletes, have been
performed with the majority showing positive results.2,21,38,39
Thus, the effects of balance ability on injury prevention
can be reliable. Even if the training program is only 1015min per day, the results were significant.40
Ankle sprains have also benefit from balance training.
While inappropriate care of ankle sprain causes recurrent
injury, balance and coordination training during the
recovery phase from a recurrent ankle sprain reduced the
risk for up to one year.39 Not limited to ankle sprains, the
risk of traumatic and overuse injuries can also be
decreased by an ankle disk and functional exercise.40 While

43
balance training helps to decrease risk of injury as well
as helps to recover from proprioceptive deficit, muscle
strengthening is another key component for athletes.

Role of the Hip Abductor Muscles

The control of the pelvic motion is critical to
maintain total body balance because the weight of the head,
arm, and trunk acts downward through the pelvis.20 Hip
abductor muscles such as gluteus medius muscle are known as
pelvic stabilizers.4 The weakness of the hip abductor
muscles may cause Trendelenburg position and inappropriate
knee alignment which potentially increase risk for overuse
knee injury or non-contact ACL tears.4 Moreover, the
weakness of these muscles may lead to postural sway; in
other words, negatively affect balance ability.

Hip Abductor Muscle Anatomy
The proximal lower extremity strength is believed to
be vital for control of hip joint position and the
resultant alignment of the distal segments.41 While
Gottschalk5 states that the function of gluteus medius is
primarily as a hip stabilizer, pelvic rotator, and regards
the role in the initiation and assistance in abduction as a

44
secondary function, gluteus medius is still recognized as
the main hip abductor muscle in general.4
Gluteus medius is a broad, thick radiating muscle on
the outer surface of the pelvis.5 Gluteus medius is curved
and fan-shaped and tapers to a strong tendon which is
attached to the anterosuperior portion of the greater
trochanter of the femur.4,5 The muscle bulk has three
distinct parts making up the fan shape.4,5,42 These parts are
equal in volume, have separate nerve innervations, and act
in different direction during gait.5,42 The posterior fibers
run almost parallel to the neck of the femur and stabilize
the hip joint by causing the femoral head to be drawn into
the acetabulum.4,5,42 The middle fibers tend to be more
vertically oriented and initiate abduction of the hip
during stance. The anterior fibers run almost vertically
from the anterior iliac crest to the top of the trochanter
and function to abduct and internal rotate the hip
joint.4,5,42 During gait, the posterior part contracts first,
followed by the middle and anterior part.5

Gluteus Medius Function and Injury
Gluteus medius is a strong abductor and medial rotator
of the thigh and important to pelvic stabilization.4,5 As
contraction of the gluteus medius prevents contralateral

45
hip drop and ipsilateral genu valgus that is known as
Trendelenburg position.6 Weakness of the hip abductor muscle
may provoke the function of the lower leg kinematics.
Kollock47 reported that weakness of the gluteus medius may
not effectively resist adduction of the femur and may place
the femur in a more medially rotated position. Also,
Hollman48 found that weak gluteus medius associated with
increased pronation at the foot. These factors may also
leads to increased tension on the iliotibial band, abnormal
patella pressure, and cause abnormal patella movement
within the trochlear groove.4,43 Thus, it may predispose
athlete to various overuse knee injuries such as iliotibial
band tightness, and patella-femoral pain syndrome.4,43 More
importantly, weakness of gluteus medius potentially
increases the risk of non-contact ACL injury. The ACL tear
is one of the very common injuries in athletic field
especially in female. The common mechanism of non-contact
ACL injury is sudden deceleration while cutting or pivoting
and landing from a jump.6,44 Jacobs45 examined the
relationship between hip abductor function and landing
kinematics between men and women. In this study, women
demonstrated lower hip abductor peak torque and increased
knee valgus peak joint displacement when landing from a
jump. Valgus loading can increase relative ACL strain and

46
may reach levels high enough to cause ligamentous failure.6
Even though the increased risk of ACL injuries is likely
multifactorial, with no single structural, anatomical, or
biomechanical feature solely responsible for this increased
rate, gluteus medius weakness could be one of the risk
factors.44
Gluteus medius contraction during single-leg stance
prevent Trendelenburg position, providing stability for
lower extremity motion.4 It is reported that the weakness of
the glutei

in general leads to progressive muscular

atrophy and the swaying gait but the absence of waddling.5
Even though it does not cause waddling, increased sway
during gait and diminished stability influences balance
ability. Trudelle-Jackson et al10 measured muscle strength
and postural stability, and asked to report incidence of
falls over the past year in elderly healthy women. They
concluded that the weak hip flexor and abductor muscle, as
well as lower values of postural stability were
significantly correlated to incidence of fall. Although
weakness of hip flexor muscle is also included to the
predictor, this study still implies the connection between
hip abductor muscle strength and balance.

47
SUMMARY

Balance ability is a vital component in the closed
kinetic chain and necessary to be a successful athlete.1-3
Balance is defined as the ability to maintain the body’s
COG within the base of support provided by the feet and is
controlled by the CNS.1,2,13,14 Three important information of
sensory sources are involved in balance ability: vision,
vestibular, and somatosensory. When all three information
sources are available, balance can be at its best.
However, when one of them is not provided, other two
components cover the gap.1-3 According to Guskiewicz1 balance
can be categorized as static, semidynamic, dynamic, and
functional balance. There are different types of device to
measure specific balance ability. The BBS is high reliable
in assessing static, semidynamic, and dynamic balance
ability, whereas the SEBT has demonstrated high reliability
for testing functional balance.1,12,23
Balance ability can be affected by many factors. One
of the most important factors for balance is proprioception.
When injury occurs such as an ankle sprain, it is believed
to cause damage to proprioceptors which in turn diminish
the ability of the CNS to control balance.1,14 Other factors
such as sport participation, positively effects balance

48
ability whereas older age, fatigue, and muscle weakness
have a negative influence on balance.3,13,14,26,29,30,32,34,35
Weakness of the gluteus medius may increase the risk
of lower extremity injuries as well as affect balance.
Since the gluteus medius acts to prevent valgus positions
at the knee as well as pronation of the foot, it may
decrease stress on knee and ankle.46 The weak gluteus medius
is typically seen in athletes who suffer from Patellafemoral pain syndrome, ankle sprain, and ACL sprain.
Therefore, several researchers suggest that strengthening
of the gluteus medius should be considered for
rehabilitation programs for these injuries as well as
injury prevention programs.6,47 From the concept of
Trendelengburg’s test, it is not difficult to see that weak
gluteus medius has a negative influence on static balance.
However, it is important to clarify the relationship among
weak gluteus medius, dynamic balance, and functional
balance. If there is also negative influences on balance
ability, strengthening of gluteus medius could potentially
help to increase balance ability as well as prevent injury.

49

APPENDIX B
The Problem

50
Statement of the Problem
All athletes require highly developed balance ability
to perform athletic movements and to prevent injury.1
Specifically, dynamic and functional balance could help
athletes to compete at a higher level the sport.14 Hip
abductor muscles are important for athletes to develop
because they function to stabilize the pelvis and control
lower limb.6,46,48 Strengthening of this muscle group may also
help to prevent inadequate joint alignment in the lower
extremity and reduce stress on the soft tissues around
these joints.46 Therefore, the purpose of this study was to
examine the relationship among hip abductor strength,
dynamic balance, and functional balance ability in
collegiate athletes.

Definition of Terms
The following definitions of terms were used for this
study:
1)

Athlete – a person who currently participates in an
NCAA Division II collegiate sport team.

2)

Balance – ability to maintain the body’s COG within
the base of support provided by the feet.1

3)

Biodex Balance System (BBS) – a devise with a circular
balance

platform

that

quantifies

the

ability

to

51
maintain dynamic bilateral and unilateral balance, as
well as dynamic LOS.28
4)

Break test – strength testing method with hand-held
dynamometer.

The

examiner

pushes

the

dynamometer

against the subject’s limb until the subject’s maximal
muscular effort is overcome and the joint gives way.49
5)

Dynamic balance – the maintenance of the COG within
the LOS over a moving base of support.1

6)

Functional balance – the maintenance of the COG within
the

LOS

over

a

moving

base

of

support

with

the

inclusion of sport-specific tasks.1
7)

Lafayette Manual Muscle Test System (MMTS) – a
held

device

for

objectively

quantifying

handmuscle

strength.
8)

Limits of stability (LOS) – the outermost range of an
area in space that a person can lean from the vertical
position in any direction without changing his or her
base of support.12

9)

Make test – strength testing method with hand-held
dynamometer.

The

examiner

holds

the

dynamometer

stationary while the subject exerts a maximal force
against the dynamometer and examiner.49
10)

Semidynamic balance – it involves one of two possible
activities: (1) the person maintains their COG over a

52
fixed

base

surface

or

of

support

unstable

while
surface

standing
or

(2)

on

a

moving

the

person

transfers their COG over a fixed base of support to
selected ranges and/or directions within the LOS while
standing on a stable surface.1
11)

Somatosensation
sensory

–

modality

a

specialized

of

touch

that

variation

of

the

encompasses

the

sensation of joint movement and joint position.1
12)

Star Excursion Balance Test (SEBT) – a functional,
unilateral balance test that integrates a single-leg
stance of one leg with maximum reach of the opposite
leg.50

13)

Static balance – the COG is maintained over a fixed
base of support either unilateral or bilateral while
standing on a stable surface.1

14)

Trendlenburg

position

–

contralateral

hip

drop

and

ipsilateral genu valgus that may occur with a weak
gluteus medius muscle.5

Basic Assumptions
The followings were basic assumptions for this study:
1)

All

participants

will

fully

understand

the

instructions provided and give a maximum effort during
testing.

53
2)

The subjects are honest in completing the demographic
form.

3)

The BBS and MMTS will be calibrated and work properly
during this study.

4)

Testing instruments (LOS testing, SEBT, and ABDT) are
valid and reliable tools for measuring the dependent
variables.

5)

All

subjects

will

volunteer

with

no

coercion

from

coaches or faculty.

Limitations of the Study
Test results can be generalized for only the NCAA
Division II collegiate athletes. Since testing was done in
the lab, the results could represent assumptive functional
measures of balance.

Significance of the Study
The scope of this study was to examine the
relationship among hip abductor strength, dynamic balance,
and functional balance ability in Division II collegiate
athletes. Balance is a necessary component to perform
athletic movement because athletes need to move their
center of gravity continuously to prevent falling.2 Hip
abductor muscles has important role in athletic performance

54
as well. Weakness of this muscle group cause Trendelengburg
position and it may lead lower extremity injury.4 Because of
this, hip abductor strengthening is recommended to add for
lower extremity injury prevention programs as well as
rehabilitation programs.4,6,7,9,20,43,45,46 Since hip abductor
muscles function as stabilizers for the pelvis and control
the lower limb, hip abductor strength may correlate with
balance ability.46 Previous research has found relationship
between hip abductor strength and experience of fall in
healthy old women as well as balance ability in individuals
with chronic ankle instability.5,10,11 However, since sports
utilize more complicated movements, it is critical to
clarify the relationship among hip abductor muscles and
specific balance ability such as dynamic and functional
balance. This information may assist athletic trainers and
conditioning coaches in determining exercises that may best
prevent injury as well as improve balance ability.

55

APPENDIX C
Additional Methods

56

APPENDIX C1
Informed consent form

57
Informed Consent Form

1.

Mizue Iwamoto, has requested my participation in a research study at this
institution. The title of the research is The Relationship among Hip Abductor
Strength, Dynamic Balance, and Functional Balance Ability.

2.

I have been informed that the purpose of the research is to examine the relationship
among hip abductor muscle strength, dynamic balance, and functional balance
ability in NCAA Division II collegiate athletes.

3.

My participation will involve the Limits of Stability (LOS) test using the Biodex
Balance System (BBS), functional balance test using the Star Excursion Balance
Test (SEBT), and hip abductor muscle strength test (ABDT) using the Lafayette
Manual Muscle Test System (MMTS). LOS test is one of the balance tests which I
will stand on a movable platform which tilt up to 20° in all directions. I will move
the platform back and forth, chasing the target which will be displayed on the
screen. SEBT is another balance test that uses a star on the floor with eight lines
extending at 45° increments from the center of the grid. I will stand on the center of
the grid with one leg and reach with the opposite leg to touch the farthest point on
the line. During ABDT, I will lie down on my back on the treatment table and my
shoulder and hip will be strapped with a belt to stabilize my body. I will push
against the researcher’s hand with maximal effort as instructed. All of the testing
will be conducted on one day in the B5 laboratory room and the athletic training
room in Hamer Hall for approximately one hour for each subject.

4.

I understand there are foreseeable risks or discomforts to me if I agree to participate
in the study. The possible risk is a falling during the LOS testing on the BBS and
functional balance testing using the SEBT where the risks of falling will be
minimized by the researcher as a spotter. Any injuries that may occur during the
balance testing can be treated at the athletic training room at Hamer Hall provided
by the researcher, Mizue Iwamoto, under the supervision of any certified athletic
trainer from California University of Pennsylvania. The risk is no more than normal
physical activity that normal athletes would be exposed during daily activity. There
is no associated risk in ABDT.

5.

There are no feasible alternative procedures available for this study.

6.

I understand that the possible benefit of my participation in the research are
contribution to existing research and may aid in enhancing injury prevention
program and/or rehabilitation program for lower extremity injury by strengthen hip
abductor muscles.

7.

I understand that the results of the research study may be published but that my
name or identity will not be revealed. In order to maintain confidentiality of my

58
records, Mizue Iwamoto will maintain all documents in a secure location in which
only the student researcher and research advisor can access.
8.

I have been informed that I will not be compensated for my participation.

9.

I have been informed that any questions I have concerning the research study or my
participation in it, before or after my consent, will be answered by

Student Researcher:

Graduate Faculty Thesis Advisor:

Mizue Iwamoto
532 3rd Street Apt#4
California, PA 15419
716-400-3060
iwa7465@cup.edu

Rebecca Hess, Ph.D
B6 Hamer Hall
California University of
Pennsylvania
California PA, 15419
724-938-4359
hess_ra@cup.edu

10.

I understand that written responses may be used in quotations for publication but
my identity will remain anonymous.

11.

I have read the above information. The nature, demands, risks, and benefits of the
project have been explained to me. I knowingly assume the risks involved, and
understand that I may withdraw my consent and discontinue participation at any
time without penalty or loss of benefit to myself. In signing this consent form, I am
not waiving any legal claims, rights, or remedies. A copy of this consent form will
be given to me upon request.

Subject's signature____________________________________ Date _______________
Other signature (if appropriate)__________________________ Date________________
12.

I certify that I have explained to the above individual the nature and purpose, the
potential benefits, and possible risks associated with participation in this research
study, have answered any questions that have been raised, and have witnessed the
above signature.

13. I have provided the subject/participant a copy of this signed consent document if
requested.
Investigator’s
signature_____________________________________________Date_______________
Approved by the California University of Pennsylvania IRB:
Start date _____/_____/____, End Date: _____/_____/_____

59

APPENDIX C2
Subject Information Sheet

60

Subject Information Sheet
Subject #_____
Age:_____

Date____________________
Gender:______

Leg dominance:________
Height: ________cm(________in)
Weight: ________kg(________lb)
Sport(s)

___________________

61

APPENDIX C3
Test Score Sheets

62
Test Score Sheet
Subject #:_______________
Date:________________
LOS score
Px trial 1

Px trial 2

Px trial 3

Px trial 4

Test trial

ABDT peak force (kg)
Distance:___________m
Px 1

Px 2

Test 1

Test 2

Test 3

Mean peak
force of 3
tests

Left leg

Right
leg

L mean peak force(__________kg) x 9.81 = ____________N
R mean peak force(__________kg) x 9.81 = ____________N

L Torque = mean force(_________N) x distance(___________m)
= _____________Nwm

R Torque = mean force(_________N) x distance(___________m)
= _____________Nwm

63

64

APPENDIX C4
Pictures of Each Test

65
Star Excursion Balance Test (SEBT)

(http://www.hhdev.psu.edu/atlab/postmed.html)

Limits of Stability test (LOS) on Biodex Balance System
(BBS)

(boyntonsportandbackpt.com/services)

66

Hip abductor muscle strength testing (ABDT) measured by the
Lafayette Manual Muscle Test System (MMTS)
MMTS

ABDT

(http://www.alimed.com/resources/common/images/products/ful
l/6132_d.jpg)
(http://www.somatics.de/Image7.gif)
The researcher will be holding the MMTS perpendicular to
the thigh at the lateral femoral condyle while subject
build their force gradually to a maximum voluntary effort.

67

APPENDIX C5
Institutional Review Board

68

69

70

71

72

73

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78
ABSTRACT
Title:

THE RELATIONSHIP AMONG HIP ABDUCTOR
STRENGTH, DYNAMIC BALANCE, AND FUNCTIONAL
BALANCE ABILITY

Researcher:

Mizue Iwamoto

Advisor:

Dr. Rebecca Hess

Date:

May 2008

Research Type: Master’s Thesis
Context:

Current research has indicated that weakness
of the gluteus medius influences balance
ability in healthy old women and people with
functional ankle instability. Previous
studies have not examined the relationship
among hip abductor strength and different
balance ability, such as dynamic and
functional balance, in healthy athletes.

Objective:

The purpose of this study was to examine the
relationship among hip abductor muscle
strength, dynamic balance, and functional
balance ability in collegiate athletes.

Design:

A descriptive correlational design was used
to determine a relationship among hip
abductor strength, dynamic balance, and
functional balance.

Setting:

The testing was performed in a controlled
laboratory setting by the researcher.

Participants:

Twenty Division II collegiate athletes
volunteered (male=11, female=9) for this
study that were currently free of injury.

Interventions: Each subject was tested on one day. All
subjects were tested by using the hip
abductor hip strength test (ABDT), the
Limits of Stability (LOS) test, and the Star
Excursion Balance Test (SEBT). The ABDT was
used to measure subjects’ hip abductor
muscle strength, and the LOS and SEBT were

79
used to measure dynamic balance and
functional balance, respectively.
Main Outcome Measures:
LOS score, SEBT score, and ABDT score were
computed from all test trials and
correlation was examined among all three
variables.
Results:

A significant correlation between hip
abductor muscle strength and functional
balance ability was present (r = .514, P
= .021). However, there were no significant
correlation between functional balance and
dynamic balance (r = .382, P = .097), or
between dynamic balance and hip abductor
muscle strength (r = -.037, P = .878).

Conclusion:

Functional balance and hip abductor muscle
strength appears to be moderately related in
healthy Division II collegiate athletes.
Since weak hip abductor may cause
inappropriate lower extremity alignment and
may increase the risk of injury,
strengthening the hip abductor muscle may
help to prevent injury as well as enhance
athletes’ performance by providing better
balance ability.

Word Count:

322