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The Effects of a Five-Week Core Stabilization-Training Program
on Dynamic Balance in Tennis Athletes
Kimberly M. Samson, BS, ATC, PES
Thesis submitted to the
School of Physical Education
at West Virginia University
in partial fulfillment of the requirements
for the degree of
Master of Science
in
Athletic Training
Michelle A. Sandrey, PhD, ATC, Chair
Ruth Kershner, RN, CHES, EdD
Allison Hetrick, MEd, ATC, CSCS
School of Physical Education
Morgantown, WV
2005
Key Words: Proprioception, Neuromuscular Control, Balance, Core
UMI Number: 1426550
1426550
2005
Copyright 2005 by
Samson, Kimberly M.
UMI Microform
Copyright
All rights reserved. This microform edition is protected against
unauthorized copying under Title 17, United States Code.
ProQuest Information and Learning Company
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All rights reserved.
by ProQuest Information and Learning Company.
ABSTRACT
The Effects of a Five-Week Core Stabilization-Training Program
on Dynamic Balance in Tennis Athletes
Kimberly M. Samson, BS, ATC, PES
There is a lack of studies in the literature pertaining to tennis athletes, core stabilization and
dynamic balance. Core stabilization and dynamic balance are important components to the sport
of tennis. The purpose of this study was to assess the outcome of a five-week core stabilization-
training program on dynamic balance. The study was a 2x2 factorial design with an experimental
and control group. This study included 13 healthy physically active collegiate level tennis
athletes and 15 subjects in the control group of aged matched activity cohorts.The five-week
protocol for the core stabilization-training program was conducted as follows: subjects followed
the program 3 times a week for an average of 30-minute sessions. There were 3 progressive
levels of exercises focusing on strengthening the core while maintaining neuromuscular control.
All subjects chosen for the study completed a pre and post-test measurement of their dynamic
balance using the Star Excursion Balance Test (SEBT). The test was conducted one week prior
to and following the five-week exercise protocol. No significant difference was found for pre-test
results for all excursions. A significant difference for time was found for pre-test and post-test
within subjects for all eight excursions (anterior, anteromedial, medial, posteromedial, posterior,
posterolateral, lateral, anterolateral). There were no significant main effects for Group or
interaction between Time and Group. In conclusion, Core stabilization-training may be used to
enhance dynamic balance in tennis athletes.
iii
ACKNOWLEDGEMENTS
I would like to thank my family, especially Mom, Dad, Jimbo, and Marta, for their
unconditional love and support throughout my journey in higher education. No words or material
possessions can ever express my gratitude for all that you have done for me, for all that you are,
and for being in my life.
I would like to thank friends, relatives and loved ones for helping me get through this project as
well as graduate school. You have been there for me and are a huge part of who I am and where I
am today.
I would like to thank Ruth Kershner, RN, CHES, EdD and Allison Hetrick, MEd, ATC, CSCS
for being on my committee and for all of your help during this past year. I greatly enjoyed
working with you and learning from you. I greatly appreciate the time you had to sacrifice out of
your schedules to guide me through this process.
I would like to thank all of the undergraduate students at Waynesburg College who
participated and completed this study. It is a wonderful feeling to know that you all took efforts
to support this project in order to see me succeed. It has been a pleasure working with you
throughout data collection and without your enthusiasm this study would not have been possible.
I would like to thank Ron Christman, USPTA for being the person who helped make this
research topic possible. I cannot thank you enough for everything that you have been for this
study. You helped me to have faith in this topic, was all ‘open arms’ about participating, helped
with resources, and provided the equipment. I could not imagine going through this without you.
I would like to thank the following staff members at Waynesburg College, who without them I
would not have been able to organize and set up data collection: Ken Alberta, MS, ATC,
Michele Kabay, MEd, ATC, Nathan Wilder, MS, ATC, CSCS and Brian Scarry. You were also a
great source of support and encouragement. Special thank you to Lee Floyd for taking all the
exercise photographs and help with technical support.
A special thank you to Dr. Michelle A. Sandrey for giving me the opportunity to be a part
of the graduate athletic training program at West Virginia University and a graduate
assistant athletic trainer at Waynesburg College. You are an unsung hero of mentoring. You
helped me in all aspects of this project from the initial steps of brainstorming, to conducting the
study and then to putting it all on paper. You gave this project many elements that no one could
have done on their own and none of it would be possible if you had not sacrificed your time,
emotions, and thought. I will forever be in debt to your support. Thank you.
iv
TABLE OF CONTENTS
ACKNOWLEDGEMENTS………………………………………………………………………iii
LIST OF TABLES............................................................................................................………..v
LIST OF FIGURES ..........................................................................................................……….vi
INTRODUCTION.......................................................................................................……………1
METHODS.....................................................................................................................………….3
RESULTS………………………………………………………………………………………..11
DISCUSSION……………………………………………………………………………………11
CONCLUSION…………………………………………………………………………………..23
REFERENCES .............................................................................................................………....24
APPENDICES ...............................................................................................................………...27
APPENDIX A: THE PROBLEM .....................................................................………....28
APPENDIX B: REVIEW OF THE LITERATURE...........................................………...33
APPENDIX C: ADDITIONAL METHODS......................................................………...66
APPENDIX D: ADDITIONAL RESULTS......................................................………….90
APPENDIX E: RECOMMENDATIONS FOR FUTURE RESEARCH………………..96
ADDITIONAL REFERENCES……………………………………………………….…………97
v
LIST OF TABLES
Tables
B1. Muscles of the Lumbar Spine………………………………………………………………..36
B2. Norris Classification…………………………………………………………………………36
B3. Synonyms for Core Strengthening…………………………………………………………..56
C1. Informed Consent Form ...........................................................................................………..66
C2. Informed Consent Form for Control .......................................................................………...69
C3. Demographic/Injury History Questionnaire.............................................................………...72
C4. Core Stabilization-Training Protocol .......................................................................………..84
C5. Dynamic Balance Test using the Star Excursion Balance Test ...............................………..85
C6. Pre-Test Data Collection Sheet for the Star Excursion Balance Test ......................……….86
C7. Post-Test Data Collection Sheet for the Star Excursion Balance Test....................………..87
C8. Jeffreys Core Stability Program…………………………………………………………….88
C9. Tests of Balance……………………………………………………………………………..89
D1. Descriptive Statistics for the Subjects……………………………………………………….90
D2. Descriptive Statistics for the Experimental Group and Control Group……………………..91
D3. Descriptive Statistics for the Pre-Test Data for the Star Excursion Balance Test ………….92
D4. Descriptive Statistics for the Post-Test Data for the Star Excursion Balance Test …………93
D5. One-Way ANOVA for the Pre-Test Data for the Star Excursion Balance Test ……………94
D6. Main Effects and Interactions for Time, Group, and Time X Group for the Star Excursion
Balance Test ……………………………………………………………………………………..95
vi
LIST OF FIGURES
Figures
B1. The Elements of Relearning a Motor Skill…………………………………………………..63
C1. Star Excursion Balance Test for a Right Limb Stance .................................………………..74
C2. Star Excursion Balance Test for a Left Limb Stance.....................................……………….75
C3. Core Stabilization-Training Program Exercises: Level 1.........................…………………..76
C4. Core Stabilization-Training Program Exercises: Level 2.........................…………………..79
C5. Core Stabilization-Training Program Exercises: Level 3.........................…………………..82
1
INTRODUCTION
The human core is described as the human low back-pelvic-hip complex with its
governing musculature.
1,2,3
The core is important because it is the anatomical location in the
body where the center of gravity is located, thus where movement stems.
1,4,5,6,7
The core
functions to maintain postural alignment and dynamic postural equilibrium during functional
activities, which helps to avoid serial distortion patterns.
8
Core stability is the motor control and
muscular capacity of the lumbopelvic-hip complex.
9
Normal function of the stabilizing system is
to provide sufficient stability to the spine to match the instantaneously varying stability demands
due to changes in spinal posture, and static and dynamic loads, within the three subsystems
proposed by Panjabi
6
(active, passive, and neural). Panjabi proposes that spinal stabilization is
dependent on interplay between passive, active and neural control systems.
10
The passive
musculoskeletal subsystem is composed of the vertebrae, facet articulations, intervertebral discs,
spinal ligaments, joint capsules and the passive mechanical properties of muscles. The active
musculoskeletal subsystem consists of the muscles and tendons surrounding the spinal column.
The neural and feedback subsystem encompasses the various force and motion transducers,
which are located in the ligaments, tendons, muscles, and neural control centers. All three
subsystems are functionally interdependent with the goal to provide sufficient stability to a spine
that faces challenges from spinal posture and static and dynamic loads.
Core strength is an essential part of any athlete’s total fitness, including tennis athletes.
Tennis athletes cannot ignore this facet in their physical training because tennis is not a one-
dimensional game; players are constantly shifting their body from side to side or rotating their
bodies toward the ball.
11
One strategic level of tennis requires that one keeps their opponents
running and off-balance, hence many directional changes during a match.
12
Core strengthening
2
and stabilization training helps to increase levels of functional strength and dynamic balance
leading to better control of balance and enhanced tennis performance.
1,2,12,13
Core muscles have
been documented during specific tennis techniques such as with the forehand drive and volley
and during serves and overhead shots.
14
The necessary mechanics and strategies utilized in tennis are widely known
15,16,17
but
through a systematic review of the literature, a lack of studies pertaining to performance
enhancement was noted, specifically regarding training of the core. Only a few studies supported
the use of a core stabilization program in athletes. Swaney and Hess
18
found positive results with
posture after a nine-week core stabilization program implemented with swimmers as a group two
times per week, using the National Academy of Sports Medicine’s standard core protocol.
Piegaro
19
found improvement in a four-week core stabilization program with exercises based on
a foam roll for twice a week and Lewarchick, et. al.
20
saw trends in performance measurements
in football athletes using a plyometric based core program for four times a week for seven
weeks. Jeffreys
21
has suggested a systematic progressive approach to introducing core
stabilization in athletes (Table C8). Based on Jeffreys and Swaney’s techniques a core
stabilization program protocol has been created by the author geared specifically toward tennis
athletes.
Although these exercises are believed to produce the desired effect, they remain
relatively unstudied.
As can be seen there is a lack of focus on core strengthening, let alone any study geared
toward tennis athletes. The Jeffreys
21
model for core stabilization specifically targets the
elements to enhance the cores functional capacity. Hence, a study examining the effectiveness of
core stabilization is warranted in tennis athletes since dynamic balance and core are essential to
3
enhance tennis performance.
Therefore, the purpose of this study is to assess the outcome of a
five-week core stabilization-training program on dynamic balance in tennis athletes.
METHODS
The design of this study was a 2 X 2 factorial design. The independent variables were
time (pre-test and post-test) and group (control and experimental). The dependent variables were
dynamic balance, measured by the Star Excursion Balance Test. Star Excursion Balance Test
measurements include anterior, anteromedial, medial, posteromedial, posterior, posterolateral,
lateral, and anterolateral excursions. Measurements were taken from subjects’ dominant lower
extremity.
Subjects
Subjects included 13 college tennis athletes that were recruited from a Division III
university using convenience sampling. They were free of lower and upper extremity pathology,
neurological, vestibular, and visual disorders, none used medication and did not perform any
core stabilization program within the past six months. Control subjects included 15 and were
recruited from undergraduate programs at Waynesburg College. They were matched to age and
activity levels of the tennis athletes. The mean age of both groups was 20.18 + 1.02 SD years,
height was 171.31 + 9.57 SD cm, and 69.92 + 15.32 SD kg in mass. Subjects signed an informed
consent form (Table C1-2) and answered a demographic/injury history questionnaire (Table C3),
which was used to obtain background information from each subject. The Institutional Review
Board (IRB) for the Protection of Human Subjects at West Virginia University approved the
study.
4
Instrumentation
In 1851, Romberg used balance tests and since then there have been more improvements
and tools.
22
Among some of these tests include objectives to measure postures from static to
dynamic states of balance (Table C9). When assessing dynamic postures, dynamic measures
should be used as opposed to static and semi-dynamic. Kinzey and Armstrong
23
report that static
measures are not good for dynamic balance because they do not take into account the shift in the
center of gravity. Static postural control measurements limit defining an athlete’s degree of
functional ability but dynamic does not.
24
Therefore functional dynamic reach tests have been
proposed. Recent tests for balance have included measures that capture dynamic balance control
while the base of support is moving.
25
The SEBT (Figure C1-2), introduced by Grey as cited in Earl
26
, challenges an athlete’s
postural control system. The test requires having the athlete maintain their base of support with
one leg, while maximally reaching in eight directions with the other leg without compromising
their base of support on the stance leg. Upon maximum reach, a light touch on the ground
without rest concludes the task for that direction, then it is back to the starting point.
24
The goal
of the SEBT is to force subjects to disturb their equilibrium to a near maximum and then return
back to a state of equilibrium.
23
The SEBT requires neuromuscular control through proper joint positioning and strength
from the surrounding musculature, throughout the test.
27
Olmsted, et al.
28
found in his studies
that the stance leg during the test requires ankle dorsiflexion, knee flexion and hip flexion, thus
the lower extremity needs adequate range of motion, strength, proprioception, and
neuromuscular control. They concluded that the SEBT is a reliable functional test that quantifies
lower extremity reach while challenging an individual’s limits of stability.
28
However, it is not
5
yet determined whether the SEBT is able to detect impairments between healthy and unhealthy
subjects.
28
Kinzy and Armstrong
23
conducted a reliability study and concluded that the SEBT
only uses quasi-static equilibrium and that the movement patterns tested are novel and not
similar to movements found in activities of daily living or sports. Results from this study and
Hertel’s study showed a strong intrarater reliability (ICC
2,1
= .67-.87) and (ICC
2,1
= .81-.96),
respectively.
Gribble
24
points out that the SEBT has a high interrater reliability and is good when it
comes to assessing dynamic balance, detecting performance deficits with musculoskeletal
injuries, and can be a possible rehabilitation tool. Hertel et al.
29
found high intratester (.78-.96,
.82-.96) and intertester reliability (.35-.84, .81-.93), with significant learning effects. Raty
30
and
Olmsted
28
in their studies concluded that the SEBT is a simple, cheap, rapid, reliable, and valid
tool that does not require special equipment and shows locomotory performance, lower extremity
functional performance, multiplanar excursion and postural control.
27,31
The SEBT has also been
found to be effective for determining reach deficits both between and within subjects with
unilateral ankle instability and is similar to measuring postural control which assesses ability to
function.
23,28
Not all the findings in the literature are positive. Kinzey and Armstrong
23
in their study to
evaluate the reliability of the SEBT using twenty subjects, found the SEBT to not be reliable and
therefore not a valid measurement tool, although they did not measure all eight excursions.
Olmsted
28
reports that there is no dynamic functional test that is considered a gold standard for
validation of the SEBT.
Learning effects, body height, leg length, and gender are found to be limiting factors.
Gribble
24
found that six practice trials in each direction are necessary to decrease any learning
6
effects, longer height and leg length will have better scores, and males will perform better.
However, foot type and minimal range of motion at the hip and with dorsiflexion did not affect
performance.
24
Six practice trials are needed due to motor learning of the task.
27
Gribble and
Hertel
27
found the role of foot type and range of motion measurements were not significant,
whereas height, and leg length were significant as factors during the SEBT and thought that
strength was a possible predictor of performance, which was not investigated in their study. It
has also been found that the different excursions each require different lower- extremity muscle-
activation patterns.
26
While other factors account for majority of variance, data should be normalized to leg
length (distance reached divided by leg length) in order to compare among subjects, since leg
length is a significant predictor of performance.
24,27
Normalizing helps to decrease gender
difference and correlation values as well.
27
Including a randomized order of testing is needed to
avoid potential learning effects and fatigue.
27
Orientation Procedures
Individuals on the men’s and women’s tennis teams at Waynesburg College were
contacted by the principal investigator, informed of this study, and asked to attend an orientation
meeting if they were interested in participating. At the orientation meeting, subjects were
explained the purpose of this study. They were also given an informed consent form and a
demographic/injury history questionnaire, explaining their rights as research subjects. Potential
subjects voluntarily filled out a demographic/injury history questionnaire as well as an informed
consent form. As part of the demographic/injury history questionnaire, the participant’s
dominant leg was noted and measured, as determined as the leg that would normally be used to
kick a soccer ball.
7
The principal investigator reviewed all completed and returned informed consent forms
and demographic/injury history questionnaires to determine which subjects were eligible for
participation in this study. Once eligible subjects were identified, they were contacted by the
principal investigator and asked to attend a second orientation meeting. At the second
orientation meeting, subjects were provided with guidelines of the testing, and their training and
testing schedule. Subjects were asked for their full cooperation and to work to the best of their
ability.
Interventions
Subjects were tested using the Star Excursion Balance Test, which tests dynamic balance,
one week prior to the beginning of the core stabilization training program (pre-test) and one
week after the conclusion of the core-stabilization training program (post-test).
This study consisted of a control group and one experimental group that performed a core
stabilization- training program for five-weeks. The subjects in the experimental group met three
times per week on alternating days to perform the training program. The estimated time for
completing the core stabilization- training program was approximately 30 minutes per session.
The training programs were administered and supervised by the principal investigator at the
Athletic Training Clinical Laboratory and Old Gym at Waynesburg College.
Control group: The control group did not perform any of the training exercises. Subjects
in this group were explained the guidelines of their group and asked to answer all questions
accurately and honestly. This ensured that they adhered to the guidelines and it helped in
controlling variables that may skew the results of the study.
Core stabilization-training group: Subjects performed a core stabilization-training
program. This program consisted of three levels with 6 exercises at each level. The subjects
8
began at exercise level one and proceeded to the next core stabilization-training program level
according to the protocol for that day (Figures C3-5). The subjects performed the core
stabilization-training program three times per week on alternating days. They performed
repetitions and sets according to the specific exercise. They progressed to the next level of the
core stabilization- training program according to the specific day of the week. Based on the
conditioning and training level experience of the Waynesburg College tennis teams, it was not
difficult to progress day by day to the next level.
A systematic literature review was completed for exercise selection, with the inclusion
criteria of any type of study that used the key words of, core, stabilization, and/or strengthening.
A general protocol was found to be consistent across the reviewed studies
5,17,21,32,33,34,35,36,37
, thus
the exercise protocol to be used in this study was derived from those sources, specifically
Jeffreys
21
categorization of progressive core exercises was used to guide the investigator in the
exercise planning. The proposed five levels used consist of mastery of core contraction; static
holds and slow movements in stable environment; static holds in unstable environment and
dynamic movement in a stable environment; dynamic movements in an unstable environment;
and resisted dynamic movement in an unstable environment (Table C8). According to McGill
38
the most justifiable approach to enhance lumbar stability through exercise entails a philosophical
approach that encourages abdominal co-contraction and bracing in a functional way. Brandon
32
adds to this by stating that core stability training needs to be conducted in a way as to effectively
recruit the trunk musculature and be able to control the lumbar spine through dynamic
movements.
The exercises start at level one which consists of exercises in a stationary position with
static contractions and then progressing to slow movements in an unstable environment (Figure
9
C3). Level two consists of exercises where static contractions will take place in an unstable
environment and progress to dynamic movements in a more stable environment (Figure C4).
Finally, level three encompasses exercises that use dynamic movements in an unstable
environment followed by a progression of added resistance to an unstable environment (Figure
C5). Exercises involved the use of the athlete’s own body weight, SwissBalls, tennis racquets,
medicine balls, and therapeutic resistance bands.
Pre-test and post-test procedures:
All subjects chosen for the study underwent a pre and post-test measurement of their
dynamic balance using the Star Excursion Balance Test (SEBT) (Table C5). The test was
conducted one week prior to and following the five-week exercise protocol. All testing was
administered and supervised by the principal investigator at Waynesburg College. Prior to
recording measurements for the pre-test and post-test on the Star Excursion Balance Test, an
explanation of each test was explained to subjects and each test was demonstrated to them. The
SEBT involved a taped star pattern with 8 projections (excursions) each at 45 degrees from each
other, on an even floor surface. Subjects placed their non-dominant foot on the middle of the star
pattern, while their dominant foot reached as far as possible in each of the 8 excursions (Figure
C1-2.) while maintaining a single leg stance while reaching with the opposite leg to touch as far
as possible along a chosen excursion. They were then instructed to touch the farthest point
possible, and as light as possible, along a chosen excursion with the most distal part of their
reach foot. Subjects were then instructed to return to a bilateral stance while maintaining their
balance. A practice session of 6 times
29
in each excursion followed by a one-minute rest and then
the measured average in inches of three trials was included in the research data. Trials were
discarded and repeated if the reach foot was used to provide considerable support when touching
10
the ground, the stance foot was lifted from the center of the star grid or if the subject was unable
to maintain balance throughout each excursion.
29
The estimated time for completing testing with
the Star Excursion Balance Test was approximately 20 to 30 minutes per session.
Data Analysis
The average scores calculated from the three trials for each excursion (anterior excursion,
anteromedial excursion, medial excursion, posteromedial excursion, posterior excursion,
posterolateral excursion, lateral excursion, & anterolateral excursion) was recorded as the
subject’s dynamic balance scores. Additionally, the leg length of the subject’s dominant
extremity was used to normalize their dynamic balance scores (excursion length/leg length x 100
for a percentage of an excursion distance in relation to the subject’s leg length) and used for data
analysis.
27
Statistical Analysis
Data obtained for the dominant extremity was analyzed for each subject. Descriptive
analysis consisted of means and standard deviations for the demographics of all subjects and
means and standard deviations for pre-test and post-test data for the SEBT. A two way one
within and one between repeated measures Analysis of Variance (ANOVA) was conducted to
determine main effects and interaction of the Star Excursion Balance Test as well as a one-way
ANOVA on pretest data between groups. The level of significance was determined by using the
Bonferroni Correction Factor(BCF) (.05/8) with a P value of p= 0.00625. Intraclass correlation
coefficients (ICCs) were conducted to determine the reliability of the measures using the Star
Excursion Balance Test on pre-test data, post-test data and combined.
11
RESULTS
Descriptive statistics for the subjects’ demographics for both the experimental and
control groups can be found in Tables D1-2. The descriptive statistics for the pre-test and post-
test data for the Star Excursion Balance Test can be found in Tables D3-4.
No significant difference was found for pre-test results for all excursions (Table D5). A
significant difference for time was found for pre-test and post-test within subjects for anterior
excursion (F
1,26
= 9.840, P= .004, ES= .275), anteromedial excursion (F
1,26
= 12.935, P= .001,
ES= .332), medial excursion (F
1,26
= 18.904, P= .000, ES= .421), posteromedial excursion (F
1,26
=
41.440, P= .000, ES= .614), posterior excursion (F
1,26
= 25.020, P= .000, ES= .490),
posterolateral excursion (F
1,26
= 26.599, P= .000, ES= .506), lateral excursion (F
1,26
= 13.395, P=
.001, ES= .340), and anterolateral excursion (F
1,26
= 18.872, P= .000, ES= .421) (Table D6).
There were no significant main effect for Group or interaction between Time and Group (Table
D6). The Intraclass Correlation Coeficiants were (ICC= .9365) for pre-test and (ICC= .9504)
for post-test measurements.
DISCUSSION
The purpose of this study was to evaluate the effects of a five-week core stabilization-
training program on dynamic balance in tennis athletes. Time was found to be significant
between the pre-test and post-test data, whereas Group was not found to be significant. Group x
Test results were not found to be significant, thus the interaction of group and test did not
significantly affect the results. There were three experimental hypotheses in this study. The first
one stated that there would be a difference between pre- and post- test results for dynamic
balance for both the control and core stabilization groups. The second hypothesis was that the
12
core stabilization training group will demonstrate greater improvement for measurements for
dynamic balance using the dominant lower extremity from pre-test to post-test and the third, that
the group performing the core stabilization training program will demonstrate greater
improvement for measurements for dynamic balance using the dominant lower extremity from
pre-test to post-test compared to the control group. The first two experimental hypotheses for the
Star Excursion Balance Test were accepted and the third was rejected.
Tennis and Multiplanar Movements as Skill Components
There are studies in the literature that pertain to shoulder mechanics necessary for the
sport of tennis however, there is only anecdotal evidence for whole body and lower extremity
movement skills needed. Similar to other sports, tennis athletes must encompass capabilities in
balance, agility, speed, quick change of direction, multiplanar movements, dynamic postural
control and flexibility.
11,12,14,15,16
Although fitness tests exist to directly measure the above
components, they are limited to the general fitness population with no standardized tests to
measure components needed in tennis specifically. The United States Tennis Association’s
(USTA) Sports Science Committee has created a High Performance Profile (HPP)
39
to aid in
providing a baseline measurement of the fitness principles as deemed most appropriate for tennis
athletes. The USTA-HPP is a single series of tests ranging from goniometric measurements of
upper and lower extremity range of motion, linear speed, agility, core stability and strength, and
scapula mechanics. Although this is a useful fitness tool, currently there are no reliability or
validity studies to assess its credibility.
For tennis athletes the core plays an integral role in multiplanar movement and postural
control. The core is comprised of the lumbo-pelvic-hip complex and is activated first prior to
13
gross body movements. Postural control is a major component necessary in tennis skills
especially the ability to move in a multiplanar fashion. Since the core has a role in being
responsible for postural control, assessments of static, semi-dynamic and dynamic balance are
alternatives to assess core stabilization. Because it is a major component necessary in tennis
skills the eight excursions included in The Star Excursion Balance Test mimic the multiplanar
directions a tennis athlete would use on the court.
1
Since the core has a role in being responsible
for postural control, assessments of static, semi-dynamic and dynamic balance are alternatives to
assess core stabilization. This study choose dynamic balance instead of a direct measurement of
core stabilization due to lack of validity and realiability for techniques suggested in the literature.
However, to make sure that the core was being activated during the training program,
observation and palpation was used to look at aberrant movement (i.e. posterior pelvic tilt),
contours of the abdominal wall (i.e. patient unable to voluntarily relax the abdominal wall),
aberrant breathing patterns (i.e. patient unable to perform diaphragmatic breathing pattern), and
unwanted activity of the back extensors (i.e. co-activation of the thoracic portions of the erector
spinae).
35
Results from our study did demonstrate improvements in excursion distances reached
perhaps related to an increase in dynamic postural control hypothesized to be attributed by the
core stabilization-training program.
Results for the Star Excursion Balance Test did indicate significant main effects for time
for all eight excursions. It is surprising that there was a significant effect for all eight excursions,
since some of them are more difficult than others (anterolateral excursion, posterolateral
excursion and lateral excursion) according to feedback from subjects in both groups. Out of all
the eight excursions the diagonal excursions (anterolateral, posteromedial, posterolateral, and
anterolateral) are the most important since human movement is multidimensional and
14
multiplanar. All eight excursions were significant between pre and post test for time, indicating
that core stabilization-training enhances multiplanar dynamic balance and movement, which can
improve tennis performance.
The posterior and posterolateral excursions were close to being categorized as significant
according to time by group interaction (Table D6). Both the posterior and the posterolateral
excursions are high in difficulty and it would make sense that the athletes in the experimental
group would have better control and coordination in those two directions as compared with the
control group, due to the core stability training program used in this study and the
multidimensional game of tennis.
11,26
Balance training tasks must be specific to the type of balance strategies required by the
sport, for example the Star Excursion Balance Test (SEBT) mimics excursions used in tennis to
prep for certain shots (i.e backhand and forehand pivot around one leg at times).
40
These
excursions are important for tennis athletes because these athletes must mimic movement in a
multi-planar fashion during training in order to transfer the effects into functional movement
during competition. Unfortunately, there are no studies reported in the literature about specific
excursions that are most adaptable to the sport of tennis or with any discussion as to difficulty
level of each excursion. However, Earl and Hertel
26
have studied lower-extremity muscle
activation during the SEBT, which can be transferred to the muscle activation in tennis.
Lower-extremity muscle activation during the SEBT was not used in this study, but a
study by Earl and Hertel
26
may provide answers to the importance of balance strategies in
tennis. Earl and Hertel
26
looked at electromyographic (EMG) activity of the lower extremity
(vastus medialis oblique, vastus lateralus, medial hamstring, biceps femoris, anterior tibialis and
the gastrocnemius) during execution of The Star Excursion Balance Test. All trials were during
15
the same day without any fitness protocol. The study used 10 healthy recreational adult athletes
and found that muscle activity of the lower extremity during The Star Excursion Balance Test is
direction dependent, with the posterior, posterolateral, lateral, and anterolateral excursions
recruiting higher activity as compared to the other excursions. In our study those excursions were
found to have improvement in mean scores with the experimental group.
It is surprising that there was no significant difference with group results. There was a
difference present for the experimental group for all eight excursions. Group means for pre-test
and post-test improved for the anterior excursion (94.16 to 99.08), anteromedial excursion (95.88
to 102.18), medial excursion (97.99 to 106.70), posteromedial excursion (100.03 to 110.99),
posterior excursion (100.62 to 110.77), posterolateral excursion (93.25 to 102.38), lateral
excursion (85.31 to 91.42) and anterolateral excursion (82.99 to 86.86)(Tables D3-4). However,
the differences in the control group were evident, but not to the same extent as the experimental
group (Tables D3-4). There were obvious differences in the mean data between groups, in which
the experimental group demonstrated greater differences between their pre-test and post-test
means as compared to the control group but no significance was noted (Tables D3-4). The
posterior and the posterolateral excursions were close to being significant, and perhaps are the
most important in tennis since tennis athletes need to be proficient at staggered diagonal stances
for serves, overhead volleys and cross court shots.
11,12,14,16
Although there are no major references to tennis athletes in regard to core and dynamic
balance training programs in the literature, there are a few studies using core stabilization
training programs that can be compared to our study.
There were no significant differences for pre-test measurements, which can be attributed
to the fact that the subjects were age match cohorts and were healthy active individuals that were
16
allowed to continue their normal physical activity. It is also assumed that none of the subjects
were currently injured at the time of testing, that control subjects were not undergoing core
stabilization-training on their own, and that there was no learning effect due to the five week
time span between pre and post-test measurements. However, in three other studies using a core
stabilization-training program, there was no significant difference or a difference in only one
variable between groups. In the Piegaro study
19
results for the core stabilization-training group
revealed no significant improvement from pre to post-test as well as when compared to the other
training groups, even though the means improved between groups. Swaney and Hess
18
noted no
difference for semidynamic balance, but did note a difference in the tested postures between
groups. However, the authors did note that the majority of the tested swimmers came in to the
study with upper cross syndrome, which was not found with the control group. Thus, the
experimental group did not have a similar posture profile comparable to the control group. This
may be related to why no major deviations would be observed between the swimmers and
control group. Twenty-four Division II collegiate football players and 18 control subjects were
tested in Lewarchick’s, et al.
20
study in which trends were found in all four tested performance
measurements in the experimental group. However, the investigators concluded that the trends
could not be attributed to the core stabilization program. Although there were some basic
similarities, in their findings, the subject population and design of the studies were different. In
the Piegaro
19
study 39 healthy subjects were divided into four groups (core, core/balance,
balance training, and a control group), whereas our study used healthy tennis athletes and an age
matched cohort physically active control group. Swaney and Hess
18
used healthy subjects for
their control group and swimmers, while Lewarchick et al.
20
used healthy controls and football
athletes.
17
Our results for group was not found to be statistically significant, but the core
stabilization-training program used can be clinically useful. Since there is no universally
accepted standard program for core stabilization, it is not known what type, frequency or
duration of exercises should be prescribed.
34
Piegaro
19
conducted a four-week program in which
the specified training programs were conducted two times a week for four weeks, instead of three
times a week for five weeks. Swaney and Hess
18
did a nine-week program, and Lewrchick
20
did
a seven-week program (4x/week for 7 weeks). In our study the core stabilization-training began
to show a difference on dynamic balance at five weeks as noted from the difference between
pretest and posttest with the improvement in excursion distance explained from the transfer of
skill effect.
1
The transfer of skill effect is when one prepares their body to adapt to movements
that will be carried over to a specific task, since it mimics the skills in that task. However, since
there is no gold standard for a core stabilization-training program for tennis athletes in the
literature, the allotted five-weeks as well as the basic nature of the exercises may not have been
conducive in gaining effects between the groups.
Since the core stabilization–training program in this study used exercises that were skill
specific to the sport of tennis (i.e. multiplanar movements for lower and upper extremity with
trunk rotation), the experimental subjects bodies were conditioned to enhance movement patterns
needed for tennis activity. Similar to our study, Piegaro
19
found increased dynamic balance in
subjects who underwent core and balance training. Piegaro found a significant difference for the
pre-test data between groups for anterolateral excursion, and a significant main effect for time
for the medial excursion, posterior excursion, and lateral excursion, and significant interactions
for time X group for the posteromedial excursion and anterolateral excursion. Piegaro’s study did
not utilize a functional core stabilization-training program that included sport specific
18
movements. His program was based in a supine position, whereas our study took movements
from tennis skills and added the core stabilization element to it. Swaney and Hess
18
conducted a
program using a core stabilization-training that included ten exercises used based on
recommendations from the National Academy of Sports Medicine, encompassing basic core
stabilization as well as stretches. Although dynamic balance was not evaluated, semidynamic
balance using the Biodex Stability System (including excursions that would be functional to
swimmers only) and posture as assessed by anterior and sagittal photos of a squat and plank
position was assessed pre and post. Lewarchick, et al.
20
used a progressive physioball core
strength program which included 6 exercises each with 3 levels of continuing difficulty. Their
assessment included 4 performance measures (abdominal endurance, velocity v-sit, vertical
jump, and the pro-agility run).
Core Stabilization
The core comprises the lumbo-pelvic-hip complex and its governing musculature which
work synergistically to produce force, reduce force, and provide dynamic stabilization
throughout the kinetic chain.
8
The quality of these actions during functional movements require
optimum neuromuscular efficiency and control.
41,42
Mechanoreceptors provide the central
nervous system (CNS) with the appropriate proprioception feedback to maintain normal length-
tension relationships and force-couple relationships through a circling effect of passive (spinal
column) to control (neural) to active (muscular) systems in order to maintain this efficient state
(inner core activated prior to outer core musculature).
43
This in turn leads to optimal
arthrokinematics in the lumbopelvic-hip complex during functional kinetic chain movements,
optimal neuromuscular efficiency in the entire kinetic chain, optimal acceleration, deceleration,
19
dynamic stabilization of entire kinetic chain during functional movements, and provides
proximal stability for efficient lower extremity movements.
8
Bouisset
9
proposed that the stability of the pelvis and trunk is necessary for all
movements of the extremities. Pelvic positioning changes actively during muscular contractions
or passively through muscular tightness, affecting pelvofemoral biomechanics.
8,44
Going down
the kinetic chain, the knee has been considered the “victim of core instability”, because hip
muscles are important for lower extremity stability and alignment during athletic movements.
9
Therefore, a need for proximal stability in order for lower extremity injury prevention is
necessary.
9
The transverse abdominal (TVA) is the first muscle to be activated within human
movement. Hodges and Richardson
9
identified trunk muscle activity before the activity of the
lower extremity, which helps the spine to stiffen leading to a foundation for functional
movements. They also found that the TVA is the first muscle to become active prior to actual
limb movement and this preprogrammed activation of the TVA was a component of the strategy
used by the CNS to control spinal stability. Richardson
45
proposed that a precise co-contraction
of the transverse abdominis and multifidus are independent of the global musculature, neutral
spine posture, and low-level continuous tonic contractions. This feedforward nature of activation
increases muscle stiffness and segmental stabilization to provide more efficient use of the
primary muscles.
46
Consequently, delayed onset of TVA activation leads to inefficient muscular
stabilization of the spine.
47
Since there is no universally accepted standard program for core stabilization, it is not
known what type of exercises as well as the training parameters that should be prescribed.
34
Gambetta has suggested that the more functional the environments are in the training, the more
20
versatile the athlete will be in handling the forces and stresses incurred by the actual sport
activity.
33,37
Overall, the exercises need to concentrate on motor control, emphasizing the neutral
spine posture, and contraction of the pelvic floor muscles and the TVA with the multifidus. The
exercises should be conducted under low level tonic contractions and progress to co-contraction
of the whole core with functional tasks gradually incorporated. Traditional rehabilitation focuses
on isolated absolute strength gains, isolated muscles, and single planes of motion. Clark, et al.
8
proposes that all functional activities are triplanar and require acceleration, deceleration, and
dynamic stability. One plane being used leads to other planes requiring dynamic stabilization to
allow for optimal neuromuscular efficiency. One needs to train dynamic stability to occur
efficiently during all kinetic chain activities, since there is a wide variety of movements
associated with athletics, athletes need to strengthen hip and trunk muscles that provide stability
in all three planes of motion.
8,9
The biomechanical aspects of the core are also important. Pelvic
positioning, rib cage positioning, neuromuscular recruitment must all be in a core stabilization
program.
48
The core stabilization training-program as demonstrated in this study included carefully
selected exercises that encompassed skill components necessary for tennis athletes however; all
the exercises can be used for any sport or athletic population. The exercises were also
specifically arranged in the training program as to follow the guidelines as proposed by Jeffreys
for the core component.
21
Thus, they incorporated center of gravity control (i.e. multi-planar
lunges), eccentric control (i.e. medicine ball twists on swissball) and isometric control (i.e.
abdominal hallowing) to enhance dynamic balance.
21
Dynamic Balance as a Component of The Star Excursion Balance Test
Assessment of dynamic balance following a training program was used in three other
studies in the literature. All three studies found an improvement between pretest and posttest
results. Blackburn and Guskiewicz
49
found significant improvement in dynamic balance but not
between groups as was evident in our study. They used subjects who were also free of lower
extremity pathology and divided them into 3 groups (proprioception training program, strength
training program and a proprioception/strength training program) while conducting dynamic
balance for the dominant lower extremity using a modified version of the Bass Test of Dynamic
Balance before and after the 6 weeks of training (3x/week for 4 weeks). Mattacola
50
found a
change in mean scores from baseline to the intervention phase after testing dynamic balance for
both the lower extremity using the Single-Plane Balance Board Test 3x/week during a 6 week
combined strength/proprioception-training program. Subjects included however, had a previous
history of first-degree lateral ankle sprains, thus not categorized as healthy. In the Piegaro, using
healthy subjects, found a difference in pretest and posttest scores with the SEBT for medial
excursion, posterior excursion and lateral excursion with an influence for group for
posteromedial and anterolateral excursions.
Making sure proper contractions occurred during the core stabilization-training program
was paramount for determining the amount of neuromuscular control that would be contributing
to the SEBT for optimum effects. However, our study did not implement any invasive techniques
for measuring muscle activation. Only subject feedback and visual observation by the principle
investigator served as the assessment of core activation. Thus, the SEBT was used as an indirect
measurement tool and cannot fully demonstrate all internal physiological parameters that would
affect performance with the SEBT. Richardson
35
has come up with the physical signs of
22
unwanted global muscle activity in order to aid in facilitating proper neuromuscular control and
this served as our guideline.
The SEBT is a great method, “to assess dynamic balance and functional capacity of the
lower extremity” when the concept of neuromuscular control is integrated in an optimal
performance enhancement program. It is important to also note that many factors contribute to
maximum excursion reach, which will vary from subject to subject. Hertel, et al.
29
proposed that
two main biomechanical principles must be demonstrated. The first, is that the subject’s, “center
of gravity must be adequately located over the base of support of the stance leg” and the second
is that eccentric and isometric neuromuscular control of the joints of the stance leg must be
efficient. Closed kinetic chain motion (ankle to hip) must be controlled by the lower extremity
muscles in order to execute the SEBT.
28
In addition, balance training tasks must be specific to
the type of balance strategies required by the sport, for example the SEBT mimics excursions
used in tennis to prep for certain shots (i.e backhand and forehand pivot around one leg at
times).
40
The data in our study normalized leg length of all included subjects as was found to be
necessary for a more accurate comparison amongst subjects from Gribble and Hertel’s study
27
.
Similar to our study Gribble and Hertel averaged three trials on all 8 excursions but with both
extremities instead of only the dominant. A stronger correlation was evident with the SEBT,
height and leg length (leg length with a higher correlation) even though male subjects had higher
excursion distances after normalizing leg lengths no significant differences were found.
It was important that this study excluded subjects with injuries within the past 6 months
because chronic ankle instability and fatigue (amplifying the trend) had effects on dynamic
postural control, using sagittal plane joint angles proximal to the ankle.
51
A decrease in reach
23
distance and knee flexion angles for all three excursions for the unhealthy ankle of the chronic
ankle instability group versus the healthy side and the healthy group was noted. Their study used
16 healthy subjects and 14 with chronic ankle instability through 5 testing sessions of the SEBT
using both legs after a specific fatigue protocol, but looked at only three excursions (anterior,
medial, and posterior). Although not measured in this study, lack of flexibility and strength in the
hip may have influenced our results when comparing excursions between the tennis athletes and
control subjects.
CONCLUSION
The results of this study indicated that there was a significant difference in dynamic
balance from pre-test to post-test, although there was not a significant difference for group, the
differences in means were more evident in the experimental group who underwent a core
stabilization-training program. Although the results of our study between groups were not
significant, enhancement of dynamic balance may result if the core stabilization-training
program is applied in the clinical setting. Studies have shown that muscle activation patterns
differ for each excursion, which demonstrates the need for a functional core stabilization-training
program to improve dynamic balance. More research is needed to determine the effects of a core
stabilization-training program on dynamic balance. In conclusion, Core stabilization-training
may be used to enhance dynamic balance in tennis athletes.
24
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2. Aaron G. The use of stabilization Training in the rehabilitation of the athlete. Sports
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3. Dominguez RH. Total body training. Moving Force Systems. East Dundee, IL.
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4. Gracovetsky S, Farfan H. The optimum spine. Spine. 1986;11:543-573.
5. Gracovetsky S, Farfan H, Hueller C. The abdominal mechanism. Spine.
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6. Panjabi MM. The stabilizing system of the spine. Part I: function, dysfunction,
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10. O’Sullivan PB, Twomey LT, Allison GT. Evaluation of specific stabilizing exercise in
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11. Shaffer A. Hard core. Tennis. 2001;37:112-114.
12. Roetert EP. Balance point. Tennis. 2002;38:48-50.
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15. Fleisig G, Nicholls R, Elliott B, Escamilla R. Kinematics used by world class tennis
players to produce high-velocity serves. Sports Biomech. 2003;2:51-71.
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16. Chow JW, Shim JH, Lim YT. Lower trunk muscle activity during the tennis serve. J Sci
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17. Liemohn W. Exercise Prescription and the back. New York: McGraw-Hill Medical
Publishing Division. 2001.
18. Swaney MR, Hess RA. The effects of core stabilization on balance and posture in female
collegiate swimmers. J Athl Train. 2003;38S:S-95.
19. Piegaro AD. The Comparative Effects of Four-Week Core Stabilization & Balance-
Training Programs in Semidynamic & Dynamic Balance. Masters Thesis, Morgantown
WV: West Virginia University. 2003.
20. Lewarchik TM, Bechtel ME, Bradley DM, Hughes CJ, Smith TD. The effects of a seven
week core stabilization program on athletic performance in collegiate football players. J
Athl Train. 2003;38S:S-81.
21. Jeffreys I. Developing a progressive core stability program. Strength Cond J. 2002;24:65-
66.
22. Donahoe B, Turner D, Worrell T. The use of functional reach as a measurement of
balance in boys and girls without disabilities ages 5 to 15 years. Pediatr Phys Ther.
1994;6:189-193.
23. Kinzey SJ, Armstrong CW. The reliability of the star-excursion test in assessing dynamic
balance. J Orthop Sports Phys Ther. 1998;27:356-360.
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26
29. Hertel J, Miller SJ, Denegar CR. Intratester and intertester reliability during the star
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2001;82:1089-1098.
27
APPENDICES
28
APPENDIX A
THE PROBLEM
Research Question
Core strength is an essential part of any athlete’s total fitness, but strength alone is not
beneficial, one needs also to be able to control the dynamic function of their core musculature
(core stabilization). The human core is described as the human low back-pelvic-hip complex
with its governing musculature.
1,2,3
The core is important because it is the anatomical location in
the body where the center of gravity is located, thus where movements stem from.
1,4,5,7
In the
literature there is a lack of focus on core stabilization, or outcome based studies using tennis
athletes. Tennis athletes cannot ignore this facet of their physical training, even though core
stabilization is not stressed in the literature for this sport. Tennis is not a one-dimensional game;
players are constantly shifting their body from side to side or rotating their bodies toward the
ball.
11
One strategic ploy of tennis requires that one keep their opponents running and off-
balance, hence causing many directional changes during a match.
12
Core stabilization and
strength training helps to increase levels of functional strength and dynamic balance leading to
better movement control and enhanced tennis performance.
1,2,12,13
Dynamic balance is an important variable because it assesses lower-extremity balance
and neuromuscular control hence, the core’s functional capacity.
26
There is no gold standard
measure for core strength, therefore dynamic balance has been chosen as a variable to indirectly
measure this as assessed by the Star Excursion Balance Test (SEBT). Since tennis is a sport that
relies on dynamic balance, the question arises as to whether a training program using core
stabilization can enhance this aspect. Therefore the research question is, what are the effects of a
29
core stabilization-training program on dynamic balance as measured by the Star Excursion
Balance Test.
Experimental Hypothesis
1. There will be a difference between pre- and post- test results for dynamic balance for both the
control and core stabilization groups.
2. The core stabilization-training group will demonstrate greater improvement for
measurements for dynamic balance using the dominant lower extremity from pre-test to
post-test.
3. The group performing the core stabilization-training program will demonstrate greater
improvement for measurements for dynamic balance using the dominant lower
extremity from pre-test to post-test compared to the control group.
Assumptions
1. All subjects will meet the inclusion criteria and not the exclusion criteria.
2. Subjects will strictly adhere to the guidelines of the control group and the core stabilization-
training group.
3. The core stabilization exercises will be challenging enough for the subjects.
4. The subjects will put maximal effort into the exercises and the SEBT.
5. Five-weeks of core stabilization training will be a sufficient amount of time to cause a change
in core stabilization and dynamic balance.
6. The Star Excursion Balance Test will be a valid method to test dynamic balance.
7. The principal investigator will be reliable for recording measurements for the Star
Excursion Balance Test.
Delimitations
1. Only college level division III tennis athletes and students (male and female) will participate,
therefore the results cannot be generalizeable to the population.
2. Only dynamic balance was tested.
3. Only the Star Excursion Balance Test was used to test dynamic balance.
30
4. Minimal research has been conducted to determine the validity for the Star Excursion
Balance Test for measuring dynamic balance.
5. The principal investigator was not be blinded to any group in the study.
Operational Definitions
1. Athletic Performance- The observable physical signs of how an athlete carries him or
herself during a sport specific task.
2. Balance- Process of maintaining the center of gravity within the body’s base of
support.
52,49,40
3. Base of Support- “Area bound by the outermost regions of contact between a body and
support surface or surfaces”.
53
4. Center of Gravity- “Point around which a body’s weight and mass are equally balanced in all
directions”.
53
5. Core- The encompassing neuromuscular group of the lumbopelvic-hip complex, with two
sections. The outer section is the rectus abdominus, external obliques and muscles that attach
to the rib cage and shoulder girdle. The inner section includes the pelvic floor muscles,
multifidus, internal obliques and the transverse abdominus.
54
6. Core Stability-Functional stability of the trunk. Appropriate biomechanical alignment from the
pelvis to the shoulder girdle with efficient coordinated neuromuscular recruitment of the
trunk.
54
7. Core Stabilization Training- Training the muscles of the lumbopelvic-hip
complex: abdominal, hip, lumbar, and pelvic muscles.
19
8. Core Strength- Develop muscles of the trunk/core area.
21
9. Dynamic Balance- Maintaining a stable base of support while the center of gravity is
changing during a prescribed movement.
24,49
10. Dynamic Postural Stability- The extent to which a person can lean or reach without moving
the feet and still maintain balance.
28
11. Functional Reach- Reaching of a limb while challenging an individual’s limits of
stability.
28
12. Golgi tendon organ- “Receptors found at the junction of the tendons and muscle fibers that
respond to both stretch and contraction of the muscle.
55
31
13. Mechanoreceptor- “A sensory receptor that responds to mechanical energy such as touch or
pressure”.
55
14. Muscle endurance- The ability to maintain a force for a period of time.
56
15. Muscle performance- Combined function of strength and endurance.
56
16. Muscle spindle- Muscle receptors that send information about muscle length and rate of
change in length.
55
17. Neuromuscular Control- The motor response to the sensory input of the muscles.
19
18. Proprioception- Recognition of sensation of joint movement and of joint position
sense.
49
19. Star Excursion Balance Test- A test, which has the subject maintain their base of support
with one leg, while maximally reaching in 8 directions with the other leg without
compromising the base of support in the stance leg.
23
The eight excursions include:
anterolateral; anterior; anteromedial; medial; posteromedial; posterior; posterolateral; and
lateral. The excursions are named according to the stance leg thus, the labeling will be
different for the right and left legs.
29
20. Strength- Maximal force a muscle can produce during a single exertion to create joint
torque.
56
Limitations
1.There were no known limitations to this study at this time.
Significance of the Study
Just like with any other athlete, tennis athletes are always in need of optimized
performance training. Part of the domain of athletic trainers is to be able to educate and promote
more efficient musculoskeletal movement in order to minimize injury risk in the athletic
population. Much of the emphasis in performance enhancement does not focus on specific
principles to help tennis athletes and thus, athletic trainers have minimal knowledge to apply any
principles clinically to their own tennis athletes.
Biomechanics and physical demands differ from sport to sport and it is the responsibility
of the athletic trainer to be able to apply various performance enhancement concepts to the
32
different populations respectively. This study would be necessary in order to contribute
information about how core stabilization training affects the athleticism of a tennis athlete as
well as introducing core stabilization exercises to enhance dynamic balance, which is important
for the advancement of overall tennis performance.
33
APPENDIX B
LITERATURE REVIEW
Introduction
The human spine is complex and even after years of research, there are still many more
questions to be explored and answered. Recently the neuromuscular system of the lumbopelvic
–hip complex, known as the core, has started to be considered the foundation where human
movement stems. Thus, this new development in core knowledge may explain more properly the
biomechanics of sports performance with implications for future improvement, which will be
beneficial for health care professionals. In order to understand the concept of core, one needs to
know the musculature, which has been broken down into an inner and outer system. Although
both systems are important, much focus has been on the inner system, which includes the
transverse abdominus and the multifidus muscles. It is also important to know about the
sensoriomotor system in particular, proprioception, which underlies the muscular function.
The core functions to maintain postural alignment and dynamic postural equilibrium
during functional activities, which helps to avoid serial distortion patterns.
8
Asymmetries in
posture and movement does not allow the core to be stable.
48
Limitations in core strength and
stability leads to inefficient sports techniques and predisposes athletes to injury.
30
The core when
working efficiently provides the neuromuscular control to maintain functional stability, thus
dynamic stability.
31
It is also the center of the functional kinetic chain which may provide insight
for enhanced sports performance techniques, after analyzing corrective factors for spinal
instability.
31
The better the neuromuscular control and stabilization strength, the more
biomechanically efficient the alignment of the kinetic chain will be, leading to more efficient
34
movement, dynamic balance, and proper posture.
1
However, measurement of neuromuscular
control to note improvement may not be evident. Few tests exist that challenge postural control
systems, specifically dynamic balance, however the Star Excursion Balance Test (SEBT) has
become that assessment tool.
29
Although the literature on the core focuses on injury prevention and rehabilitation, the
scope of this literature review will be on enhanced sports performance, in particular with the
tennis population due to its demands for proper core functioning. The kinetic chain concept
validates core stabilization training, which may increase dynamic balance and together with
correct postural alignment, spinal stabilization can be achieved. In this review of the literature,
information will include anatomy of the core; importance of muscle co-contraction; core
stabilization; the core as a link to kinetic chain movement; proprioception and neuromuscular
control; dynamic balance and posture; Star Excursion Balance Test; biomechanics of tennis; and
core stabilization-training programs.
Anatomy of the Core
The core encompasses the lumbopelvic-hip complex (with 29 muscles of insertion) in
which the center of gravity is located and where all movement begins.
8
The muscular system of
the core provides the major support to the loaded spine during functional normal range of motion
as well as physiologic function.
45,57
Activity of the trunk muscles as well as the ligaments are
essential for maintaining stability and dynamic control of the lumbar spine to any unstable
areas.
58,59
Muscles of the lumbar spine, abdomen, and hip have been found to produce force,
reduce force, and provide dynamic stabilization, while working synergistically.
8
There is no universally accepted definition of what “core” is, but a few have embarked on
creating an organized framework for reference. Bergmark
10,46
and Konin
60
have categorized the
35
musculature of the core into two categories for simplicity when discussing core stabilization. The
first is the global system (external core), consisting of the gluteus maximus, and erector spinae as
well as other muscles shown in Table B1. These muscles are the large torque-producing muscles
linking the pelvis to the thoracic cage, lying more superficially, and producing the gross trunk
movements.
34
The second system is the local (internal core) muscles (Table B1), which are the
deep muscles with origins or insertions into the lumbar vertebrae. These muscles are ideal for
controlling intersegmental motion, because they are close to the center of axis of rotation of the
spinal segments and are generally shorter in length.
46,60
Recent research
34,58
has suggested that
the two proposed systems constituting the core, although work synergistically, may be activated
at different times, with the inner core muscles activated first, as the transverse abdominis (TVA)
and multifidus contract separately from the global muscles.
34,58
Norris
44
has proposed to
categorize the core into a postural muscle system, either as postural or phasic muscles. He
suggests that the postural muscles are the ones that are primarily tighter in the population, while
the phasic muscles are the weaker ones (Table B2). Bergmark
61
, Konin
60
and Norris
44
share
similar findings. The global muscles from Table B1 are included in the same list as in the phasic
muscles in Table B2, indicating that these muscles do not work as intrinsic stabilizers but rather
as an external source for additional strength. However, it is difficult to explain the differences
between the two systems, as one is used for anatomical reference whereas the other explains
upright posture.
King
54
proposed that appropriate biomechanical alignment from the pelvis to the shoulder
girdle along with efficient coordinated neuromuscular recruitment of the trunk, constitutes a core
broken down into thirds. The lower third being the hips and pelvis, the middle as the muscular
abdomen and the upper third the rib cage and shoulder girdle.
54
The middle one-third of the core
36
is the soft tissue and neuromuscular center and guides positioning of the upper and lower
third’s.
48
Overall, the contribution of different muscle groups to lumbar spine stability depends
on the direction and magnitude of trunk loading, with optimal core function exhibiting normalcy
in trunk mobility and stability.
9,48
Table B1. Muscles of the Lumbar Spine
31
Global Muscles
Local Muscles
Rectus abdominis
Multifidi
External Oblique
Psoas Major
Internal Oblique
Transversus abdominis
Iliocostalis
Quadratus Lumborum
Diaphragm
Internal Oblique (posterior fibers)
Iliocostalis/Longissimus (lumbar portions)
Table B2. Norris Classification
44
Postural
Phasic
Quadratus Lumborum
Rectus abdominus
Erector Spinae
Internal/External Oblique
Iliospsoas
Gluteals
Tensor Fascia Latae
Quadriceps
Rectus Femoris
Tibialis Anterior
Piriformis
Peronei
Pectineus
Adductors
Hamstring
Gastrocnemius
Soleus
Tibialis posterior
More information is needed to discuss the mechanisms by which muscles provide
stability to the spine.
57
Studies
59,62
have looked at these individual muscles in order to quantify
their role in core dynamics, using biomechanical models or through electromyelographic (EMG)
analysis. McGill, et al.
59,62
has shown that EMG is a good diagnostic tool to use when checking
the activity of deep abdominal muscles and the best tool to investigate the spine as long as the
37
magnitude of error is recognized. It is also a useful tool when it comes to verifying the
involvement of muscles in various situations.
63
Contribution of muscles associated with movement of a limb, other than the prime
movers, have been shown to contribute to the maintenance of both the position of the center of
mass over the base of support and the stability of affected joints. This explains a “feedforward”
mechanism which is not initiated by feedback from the limb movement.
58
At onset of body
movement, activated muscles take on roles as force generators and as stabilizing springs to avoid
the need for active neuromuscular responses to small disturbances. The neuromuscular system
produces coactivation of muscle activity, which stabilizes limb segments making it easier to
control the trajectory of a body segment during targeted movements.
64
Hence, there are coupled
dynamics within lower extremity body segments.
65
It is postulated that stability of the spine
stems from antagonistic flexion and extension muscle coactivation forces, intra-abdominal
pressure and abdominal spring force.
34
It is important to note that the activity of specific lumbar
muscles is heavily dependent on the task to be performed, also taking into account the position of
the body segments.
63
Researchers have performed studies
9,34
evaluating various contributing factors to core
neuromuscular functioning. Arokoski
34
found that women are better able to activate
stabilization–trunk muscles versus men, but mentioned that men only need to activate a small
amount due to a larger muscle mass versus women.
Leetun
9
looked at core stabilization strength
measures between males and females.
Leetun
9
noted that females had less hip extension strength
and greater trunk extension endurance, while males had greater quadratus lumborum endurance
and isometric hip abduction as well as greater hip external rotation torque. It was concluded in
38
his study that females have a lower stable foundation upon which to develop or resist force in the
lower extremity.
Many studies
31,58,46,47
in the literature have evaluated specific muscles of the core to
examine their properties and contributing roles. Recent research
31,58,46,47
has emphasized the
importance of the TVA and the multifidus muscles, although all core muscles are needed for
optimal stabilization and performance. The deep core muscles are important for controlling trunk
stability, especially the TVA.
58
The TVA creates a rigid cylinder when contracted thus creating
lateral tension through the transverse processes of the lumbar spine, leading to decrease
translational and rotational motion of the spine, along with anterior pressure and increased
stabilization of the spine to withstand a variety of postures and movements.
47
Cresswell as cited
in Johnson
46
noted that the TVA was continually active in isometric and dynamic trunk
movements versus the phasic manner of the rectus abdominis and obliques, with the unique
function of creating intra-abdominal pressure (most closely linked) as well.
The TVA is the first muscle to be activated within human movement. Cresswell as cited
in Johnson
46
as well as other studies
58,47
have indicated that the TVA precedes acceptance of
external loads and the onset of other muscles prior to movement.
Hodges and Richardson
9
identified trunk muscle activity before the activity of the lower extremity, which helps the spine
to stiffen leading to a foundation for functional movements. They also found that the TVA is the
first muscle to become active prior to actual limb movement and this preprogrammed activation
of the TVA was a component of the strategy used by the central nervous system (CNS) to control
spinal stability. Richardson
45
proposed that a precise co-contraction of the transverse abdominis
and multifidus are independent of the global musculature, neutral spine posture, and low-level
continuous tonic contractions. The CNS stabilizes the spine by contraction of the abdominal and
39
multifidus muscles in anticipation of reactive forces produced by limb movement.
58
This
feedforward nature of activation increases muscle stiffness and segmental stabilization to provide
more efficient use of the primary muscles, as was noted by Johnson in glenohumeral range of
motion.
46
The TVA, with its horizontal fiber arrangement, functions independantly from the
other abdominal muscles, and along with the internal oblique it enhances the stiffness of the
spine in a general manner (not in specific direction).
58,60
Consequently, delayed onset of TVA
activation leads to inefficient muscular stabilization of the spine.
47
In scholarly as well as secular journals, the abdominal musculature are usually the
primary focus in discussions of the core, because the abdominals are an important component of
the core musculature.
31
This muscle group is important for the function of stabilizing the spine
and has been validated in numerous studies.
43
With such an importance it has been concluded
that the average athlete often trains the abdominal muscles inadequately versus other muscle
groups.
13
Norris
44
analyzed the abdominals during exercises and found that the internal oblique
and the transverse abdominus are continuously active during standing. The TVA, pelvic floor
muscles and the oblique muscles were found to increase intra-abdominal pressure with the
thoracolumbar fascia, creating lumbar functional stability.
31,66
Hodges, et al.
47
studied EMG
analysis of abdominal muscles with upper extremity movements and found that the TVA was the
first muscle to be activated, hence its role in spinal stiffness, while those with low back pain had
an offset timing of their TVA. Drysdale, et al.
67
looked at EMG activity of the rectus abdominus
and external obliques during pelvic tilt and abdominal hollowing exercises and found that the
pelvic tilt recruited the muscles better versus abdominal hallowing and the hallowing needed
little activation of the global musculature in order to perform. Cholewicki, et al.
68
observed a
constant level of internal oblique muscle activity regardless of trunk angle, along with minor
40
multifidus involvement. Leetun
9
found that the abdominal muscles control external forces that
may cause the spine to extend, laterally flex, and rotate, and will increase stability of the spine
through co-contraction with lumbar extension.
The deep posterior back muscles are important to the core as well. The erector spinae and
intrinsic muscles (rotators, intertransversi, multifidi) work as segmental stabilizers.
31
The erector
spinae also has a balancing and stabilizing role.
69
The multifidus has been shown to be similar to
the TVA, because it is tonically active, increases segmental stiffness, is considered to adjust
small movements of the vertebrae rather than act as a primary mover.
58
Although important,
these lumbar paraspinal muscles have been found to be weaker with excess fatigability,
providing evidence for their importance in core rehabilitation protocols.
34
Even though not
comparable in size to the abdominals and weaker, this muscle group has been used in low back
studies to explain their major part in daily trunk movement. Cholewicki and McGill reported in
O’Sullivan,
10
noted that low levels of maximal voluntary contraction of the segmental muscles
are required to ensure the stability of the spine ‘in vivo’ and that co-contraction of anterior and
posterior spinal musculature is important in providing stability during various types of motion.
70
Cholewicki and McGill
71
stated that EMG evidence indicates the importance of local
musculature in providing spinal segmental stabilization and that a small increase in local
musculature prevented spinal instability versus contraction of the global musculature alone.
46
Raschke and Chaffin
72
found that muscles of the deep local system were actively supporting the
spine during such shear loading versus the global muscles with EMG readings. However, another
study
46
observed that increase co-contraction of global muscles of the trunk was proportional
with increase compression and spinal loading.
41
Other core musculature and soft tissues of importance but not heavily researched consist
of the thoracolumbar fascia, quadratus lumborum (QL), diaphragm and muscles of the hip (i.e.
psoas, hamstrings, gluteus maximus). The thoracolumbar fascia has been considered the
“nature’s back belt”, with its posterior layer serving the most important role in supporting the
lumbar spine and abdominal muscles, it is usually associated with the TVA-intradominal
pressure system.
31
Contraction of the TVA and obliques, which attach to the fascia, create a
tension effect which increases intra-abdominal pressure of space and muscles, providing a more
sturdy environment around the lumbar spine.
It provides a link between the lower and upper
extremity and will act as a proprioceptor upon muscular contraction.
31
The QL muscles, usually
working isometrically are considered to be major stabilizers of the spine, and are emphasized to
be necessary in a core program.
31,73
Due to its architectural features and location the QL muscles
produce lateral trunk flexion and lumbar flexion and extension.
9
When the QL contracts it
produces a torque, which will affect movements and stability of the spine and pelvis in two
planes (sagittal and frontal).
63
Within the kinetic chain the hip muscles are important, especially
with transferring forces from the lower extremity to the spine during upright activities.
31,56
Neptune et al.
65
conducted a study where he established a database of kinematic and EMG data
during cutting movements. Findings indicate that lower extremity muscles functioned similarily
with side-shuffles and v-cut movements. Hip and knee extensor muscles also function to
decelerate the center of mass during landing and propulsion phases upon toe-off. He concluded
as well that the gluteus medius and adductor magnus isometrically stabilize the hip rather than
produce mechanical power. The diaphragm has been considered as the roof of the core,
suggesting that breathing techniques may be important in a core–strengthening program.
31
42
Importance of Muscle Co-Contraction
The core pelvic originating muscles (spanning the maximum number of joints) were
shown to be 90% more effective at laterally stabilizing the spine.
74
Previously it was thought that
the pelvic floor muscles work alone. Now it has been shown that the abdominals work together
(with different forces, etc) and along with the unique TVA properties so that the “core” of the
human body can be more readily explained and examined.
66
Researchers have taken advantage of
this concept as seen in the literature, however there is a need for further research in the area of
trunk muscle performance.
75
A study by Cholewicki, et al.
68
examined co-activation of trunk flexor and extensor
muscles in healthy individuals and found that antagonistic trunk muscle coactivation is necessary
to maintain the lumbar spine in a mechanically stable equilibrium.
68
Beimborn et al.
75
concluded
that trunk extensors should be 30% stronger versus the flexors in most conditions.
Chow et al.
16
found that both bilateral and co-activation of abdominals and low back lower trunk muscles are
unavoidable during trunk movement, because they function as units to maintain balance between
mobility and stability of the spinal column. Cholewicki et al.
68
observed that antagonistic trunk
flexion-extension muscle coactivation was present around neutral spinal posture in healthy
individuals. Using a biomechanical model, the co-activation was explained entirely on the basis
of the need for the neuromuscular system to provide the mechanical stability to the lumbar spine.
Norris
44
noted that imbalances of muscles leads to alteration of pelvic tilt and decrease range of
motion in spinal flexion.
Gracovetsky
5
stated that musculature of the lumbar spine is of primary importance in the
control of the efficiency of the spinal mechanism.
The lumbar region of the vertebral column
43
transmits a large proportion of the body weight to the pelvis plus additional forces due to muscle
action and external loads.
76
Hence, there is maximal activity of trunk muscles during different
postures.
16
Most important, lumbar fatigue impairs the ability to sense a change in lumbar
position and thus the perception of trunk position leading to unnecessary motion for correct
placement of the trunk.
77
Few ergonomic studies have looked at the ‘twisting’ phenomenon. There is limited
knowledge of the muscular response throughout the twisting range of motion, besides what is
known. Trunk muscles are inhibited during twisting efforts, they maintain equilibrium about all
axes, and that the axial trunk twisting and generation of axial torsion are the result of muscular
force.
69
Previous studies of twisting have revealed substantial cocontraction of agonist and
antagonist muscles within the torso when torsional movements are generated.
78
Biomechanical
relationships of supporting structures within the torso are altered by twisted postures.
78
There is
no trunk muscle specifically designed to produce axial rotation because of a combination of
planes, so the cocontraction of several core muscles is important.
69
Core Stabilization
Core stability is the motor control and muscular capacity of the lumbopelvic-hip
complex.
9
Normal function of the stabilizing system is to provide sufficient stability to the spine
to match the instantaneously varying stability demands due to changes in spinal posture, and
static and dynamic loads, within the three subsystems proposed by Panjabi (active, passive, and
neural)
6
. Panjabi proposes that spinal stabilization is dependant on interplay between passive,
active and neural control systems.
10
The passive musculoskeletal subsystem is composed of the
vertebrae, facet articulations, intervertebral discs, spinal ligaments, joint capsules and the passive
44
mechanical properties of muscles. The active musculoskeletal subsystem consists of the muscles
and tendons surrounding the spinal column. The neural and feedback subsystem encompasses the
various force and motion transducers, which are located in the ligaments, tendons, muscles, and
neural control centers. All three subsystems are functionally interdependent with the goal to
provide sufficient stability to a spine that faces challenges from spinal posture and static and
dynamic loads. In a sense, Panjabi
6
with his proposed model summarizes the already known
phenomenon of the human neurological reflex system used to maintain upright posture. The
passive subsystem is the first to detect changes in posture, which then signals the neural
subsystem to detect the variations and consequently provide input to the active subsystem, which
will provide efferent signals to the muscles in order to correct the initial imbalance. Hence,
spinal stabilization leads to individual muscle tensions dependant on dynamic posture (variation
of lever arms and inertial loads of different masses).
6
There are different opinions on the definition and assessment of core stabilization.
Panjabi, based on research studies, refers to the core as the control of intersegmental motion
around a neutral zone, which is the primary parameter of spinal stability. The neutral zone is the
range of physiological motion measured from the neutral position, within which the spinal
motion is produced with minimal internal resistance. Neutral position is the posture of the spine
in which the overall internal stresses in the spinal column and the muscular effort to hold the
posture are minimal. An increase in the neutral zone is a more significant indicator of spinal
instability, following trauma versus an increase in total physiologic range of motion.
46
Panjabi, et
al.
57
noted that the neutral zone is a better indicator of spinal stability versus range of motion.
The mentioned biomechanical model should not be confused with practical means. Clinical
instability describes a significant decrease in the capacity of the stabilizing system of the spine to
45
maintain the intervertebral neutral zones within physiologic limits, which results in pain and
disability and leads to insufficiency of the muscle system.
46
The stabilizing system of the body has to be functioning optimally to use effectively the
strength, power, neuromuscular control and muscular endurance that have been developed in
prime movers.
8
The primary role of dynamic stabilization and segmental control to the spine
comes from the deep abdominal muscles.
10
Thus, a strong stable core improves optimal
neuromuscular efficiency throughout the entire kinetic chain, improving dynamic postural
control, which is why it has been suggested that good trunk muscle strength enhances
performance.
8,21
The core functions to maintain postural alignment and dynamic postural equilibrium
during functional activities, which helps to avoid serial distortion patterns.
8
Asymmetries in
posture and movement does not allow the core to be stable.
48
Limitations in core strength and
stability leads to inefficient sports techniques and predisposes athletes to injury.
30
Instability is
the loss of motion segment stiffness.
79
Pope and Panjabi
79
advocate a biomechanical approach to
define instability.
In an efficient state, each structural component distributes weight, absorbs
force and transfers ground reaction forces.
8
There is a circling effect of passive (spinal column)
to control (neural) to active (muscular) systems in order to maintain this efficient state.
43
An
efficient core maintains normal length-tension relationship of functional agonist and antagonists,
leading to normal force-couple relationships. This in turn leads to optimal arthrokinematics in the
lumbopelvic-hip complex during functional kinetic chain movements, optimal neuromuscular
efficiency in the entire kinetic chain, optimal acceleration, deceleration, dynamic stabilization of
entire kinetic chain during functional movements, and provides proximal stability for efficient
lower extremity movements.
8
46
The Core as a Link to Kinetic Chain Movement
Bouisset
9
proposed that the stability of the pelvis and trunk is necessary for all
movements of the extremities. Pelvic positioning changes actively during muscular contractions
or passively through muscular tightness, affecting pelvofemoral biomechanics.
8,44
Going down
the kinetic chain, the knee has been considered the “victim of core instability”, because hip
muscles are important for lower extremity stability and alignment during athletic movements.
9
Therefore, a need for proximal stability in order for lower extremity injury prevention is
necessary.
9
Muscle stiffness is a significant factor in controlling spinal stability. A decrease in
muscle stiffness leads to instability and eventually injury, etc.
46
The muscle system may
compensate for instability by increasing the stiffness of the spine and decrease the size of the
neutral zone.
46
The core is a muscular corset that stabilizes the spine and body, with and without limb
movement and is the center of the functional kinetic chain.
31
The core operates as an integrated
functional unit, with the entire kinetic chain working synergistically to stabilize dynamically
against abnormal forces.
8
The kinetic chain operates as an integrated, interdependent, functional
unit, which strives for functional strength and neuromuscular efficiency.
8
Functional strength has
been described as the ability of the neuromuscular system to reduce force, produce force, and
stabilize dynamically the kinetic chain during functional movements on demand in a smooth
coordinated fashion.
24
An improved ability to control the trunk and pelvis under various static and dynamic
conditions may enhance sports performance and prevent various injuries.
80
The stabilization of
the core addresses static postural alignment which facilitates appropriate anticipatory postural
47
activity of the feed-forward system (weight bearing and functional movement patterns re-
organizes the feedback systems). Functional motions integrate the neuromuscular coordination
between the trunk and the upper extremities, which leaves the body as a linked system that can
now move without referring to static start position available range of motion or dynamic stability
(functional stability).
54
The closed and open kinetic chain is in direct relationship to balance.
52
The closed chain
nature of athletic activities, especially tennis, describes the distal end of a segment as relatively
fixed, with motion at one segment influencing that of all other segments in the chain.
9
Leg and
trunk muscles exert indirect forces on neighboring joints through forces among body segments.
52
Closed kinetic chain motion (ankle to hip) must be controlled by the lower extremity muscles in
order to execute the SEBT.
28
Core stability leads to a more biomechanically efficient position for the entire kinetic
chain.
8
A change in the position of the center of mass by limb movement leads to dynamic forces
transmitted to the body via inertial reactions between segments, thus a stable core is needed to
efficiently transmit these forces.
47
Cholewicki
9
says that kinematic responses of the trunk during
sudden events depends on both the mechanical stability level of the spine before loading, and the
reflex response of the trunk after loading.
9
Functional stability of the upper quarter is linked to
core stability.
54
Proprioception and Neuromuscular Control
Multiple definitions for proprioception exists, in which the afferent input of joint position
sense and kinesthesia is used, or as defined in the broader context of neuromuscular control.
36
Proprioception is one of the somatic senses (mechanoreceptive senses of tactile and position
48
sense) and is the recognition of kinesthesia sensation of joint movement and of joint position
sense, with the strength of the muscles around a joint contributing to proprioception.
36,49
Another
way to describe proprioception is the afferent information coming from the internal peripheral
areas of the body which contribute to posture and joint stability.
41
Proprioception encompasses
two aspects of position sense both static and dynamic”.
36
Dynamic sense (kinesthesia) provides
feedback to the neuromuscular system about information regarding movement.
36
It is a complex
neuromuscular process with afferent input and efferent movement, allowing the body proper
stability and orientation during static and dynamic activities.
36
Proprioception is a type of feedback system to obtain awareness of posture, movement
and equilibrium changes in relation to the body.
36
The CNS “processes incoming afferent
proprioceptive input by comparing actual with intended movements” and “this discrepancy can
trigger efferent output to correct the error”.
36
Proprioception is a distinct component of balance
and dynamic joint stability, with the cumulative neural input to the CNS from the
mechanoreceptors in joint capsules, ligaments, muscle tendons and skin, as well as the
integration of afferent neural input to the CNS contributing to the body’s ability to maintain
postural stability.
36,50
The human organism uses the redundancy within the sensorimotor system
to reduce this variability when realizing the solutions to a given task.
23
Dynamic joint stability is
the end point of the proprioceptive system”.
36
The process of feedforward are anticipatory
actions that occur before the sensory detection of a homeostatic disruption.
41
Until feedback
controls are initiated the afferent information is used intermittently.
41
Proprioceptive
neuromuscular facilitation is needed for the cocontraction of the core muscles.
31
Deficits in
proprioception are evaluated through balance tests.
50
49
Mechanoreceptors “initiate the afferent loop of proprioceptive feedback to the brain” and
are “specialized end organs that convert specific physical stimulus’s into neurological signals”
that are “acted upon by the CNS to modulate joint position and movement”.
36
There are skin
receptors such as the Pancinian Corpuscles and Ruffini Endings which take into account
superficial movement or touch outside the body and turn them into mechanical signals to the
brain, which is part of the overall proprioception of that particular body part. Mechanoreceptors
in supraspinal ligaments reflexively elicit upon mechanical deformation activity of paraspinal
muscles.
70
The muscle spindles and Golgi tendon organs are the muscle receptors.
36
The pertinent
mechanoreceptors of focus are found in the joint capsules, ligaments and muscles, comprising of
the golgi tendon organs that concentrate on active muscle tension and the muscle spindles, which
focus on muscle length changes.
36,41
Changes in spinal stability provide a physical stimulus to
the specific mechanoreceptor (detecting the mechanical deformation of the receptor itself or of
adjacent cells) which creates a change in its membrane potential, thus a neural signal of tension
(action potential) is sent off to the CNS.
36,41
This afferent input goes to the spinal cord level
connecting to neurons of higher CNS levels.
41
The brain stem and the cortex filter and modulate
the sensory input that will enter the ascending tracts, which are the specific neurons grouped for
the purpose of a one-way highway outlet for incoming signal processing to the brain.
41
For
example, mechanoreceptors in ligaments are found in the connective tissue running parallel to
the ligamentous fibers. When ligament tension occurs from changes in muscle length or velocity,
a compression of the connective tissue takes place which stimulates the mechanoreceptors.
36,41
Thus, tissue injury to the osseous and ligamentous structures can cause functional instability, if
the mechanoreceptors are unable to fire properly due to physical damage.
31
50
The ligaments are important for the passive stiffness of the lumbar spine and are thought
to provide afferent proprioception of the lumbar spine segments.
31
There are numerous ligaments
to account for that run along the zygoapophyseal (facet) joints, pedicle, lamina, and the pars
interarticularis. Toward the end ranges in spinal motion the ligaments develop reactive forces
that enable them to resist spinal motion, but do not cause motion.
6
Although part of the passive
subsystem, they are also part of the neural subsystem for they are dynamically active in
monitoring the transducer signals.
6
“The spinal ligaments provide little stability in the neutral
zone. Their more important role may be to provide afferent proprioception of the lumbar spine
segments” at the end range of motion.
31
Neuromuscular control is the nervous system control over muscle activation plus the
other factors leading to task performance.
41
Neuromuscular recruitment in the desired patterns for
successful performance is needed in increasing motor skills.
42
Neuromuscular efficiency is
postural alignment (static/dynamic) and stability strength, which allows the body to decelerate
gravity, ground reaction force, momentum at tight joints, in the right plane and at the right time.
8
It also has been described as the ability of the CNS to allow agonists, antagonists, synergists,
stabilizers, and neutralizers to work efficiently and interdependently during dynamic kinetic
chain acitivites.
8
Proprioception and muscular strength regulate balance and joint stability by
neuromuscular control.
49
Two studies supports Panjabi’s hypothesis that the stability of the
lumbar spine is dependant not only on the basic morphology of the spine but also on the correct
functioning of the neuromuscular system, including proprioceptive stimulation to retain muscle
and trunk stabilization.
10,43
51
Dynamic Balance and Posture
“Core strength is an integral component of the complex phenomena that comprise
balance” and is “important for functional activities”, thus balance is key to athletic
performance.
31,49
Gambetta and Gray as mentioned in Blackburn
49
refer to balance as “the single
most important component of athletic ability” and is involved in nearly all forms of movements.
Maintaining balance is the ability to maintain a position and to voluntarily move, which are
important for sport balance.
40
Balance is the state of bodily equilibrium or the ability to maintain
the center of body mass or center of gravity over the base of support without falling.
52,49,40
Interestingly, the human body is a tall structure balanced on a relatively small base with the
center of gravity positioned high (above the pelvis), creating a daily challenge to our
physiology.
52
Upright posture is a complex task and maintaining balance is an ever changing
skill.
81,82
Balance is a motor skill of clinical relevance, because deficits may inhibit lower
extremity function and it has everything to do with posture.
24,28
In order to maintain postural
control, the body is in a state of continuous movement in order to maintain balance, adjusting to
keep the center of gravity over the base of support.
28
Maintenance of postural control requires
preprogrammed reactions, nerve-conduction velocity, joint range of motion and muscle
strength.
28
Dynamic balance is required for activities of daily living and is necessary for complex
weight-shift activities in standing.
23,22
It may be described as maintaining a stable base of support
while completing a prescribed movement, while there is a changing base of support.
24,49
Dynamic
activities cause the center of gravity to move in response to muscle activity.
23
All systems that contribute to balance will affect sports performance.
40
Balance control is
multidimensional, with complex sensory, neuromuscular and central processing systems.
25
Balance and joint stability depend on sensory input from peripheral receptors with visual,
52
somatosensory, and vestibular systems all contributing to maintenance of balance.
23,49
Maintenance of the state of dynamic equilibrium needs systematic involvement with feedback
from the ocular, vestibular, kinesthetic and auditory systems.
83
Postural balance is evaluated to
determine the combination of peripheral, vestibular, and visual contributions to neuromuscular
control.
84
Dynamic postural impairment may be influenced by impaired proprioception and
neuromuscular control, strength, and range of motion, to name a few. Strength demands are most
likely greater when performing dynamic tasks versus static tasks.
28
Balance does not work in
isolation and poor balance leads to poor technical skill and skill development.
83
Balance is the
single most important component of athletic ability because it underlies all movement.
83
Dynamic balance is important for an athlete because falls will result if the athlete’s strategies are
unsuccessful and inefficient balance strategies will result in poor athletic performance.
40,83
For
example, during running the body is placed forward beyond the base of support and then the
balance is regained when the leg is brought forward to catch the body.
40
So during running and
cutting activities, balance is lost and regained.
40
There is also continual reaction to external
forces in athletics (i.e. court, opponents, ball, weather, gravity, limb movement) which constantly
imposes balance challenges.
83
Horak as cited in Irrgang
40
defined postural control as the ability to maintain equilibrium
and orientation in the presence of gravity. It is necessary to have this postural control in order to
have balance and that the body makes many adjustments to maintain balance.
It is said that the
assessment of postural control testing became popular after Freeman developed tests of dynamic
balance that test the athletic population.
24,85
Outcome measures in static positions was the
standard in assessing performance criteria and now production measures (dynamic balance i.e.
SEBT), are found to be better indicators of core stabilization and biomechanics.
42
Assessing
53
dynamic postural stability aids in assessing joint instability more effectively versus static
testing.
86
Testing dynamic postural control often involves completing a functional task without
compromising the base of support, with proprioception, range of motion, and strength, as extra
components needed.
24
The greater time spent in former athletic participation and in current
activity level have been found to increase performance on dynamic balance tests and a decrease
in score with increasing age.
30
Balance training tasks must be specific to the type of balance strategies required by the
sport, for example the Star Excursion Balance Test (SEBT) mimics excursions used in tennis to
prep for certain shots (i.e backhand and forehand pivot around one leg at times).
40
Maintenance
of balance during dynamic movements (such as with the SEBT) involves the ability to keep the
center of gravity over the stable base of support without losing one’s balance.
28
Biomechanics of Tennis
There is limited research regarding the biomechanics of tennis with the majority focusing
on the tennis serve and shoulder mechanics. However, there are many implications to the trunk,
which cannot be ignored when analyzing the tennis serve. For example, one’s arm angle is due to
lateral trunk tilt, whereas shoulder internal rotation and trunk rotation occur prior to impact on
the serve, with the trunk angular velocity being important.
15
Interestingly, fifty-four percent of
forces during the tennis serve come from the trunk and lower quarter.
54
Liemohn
17
stated that
muscle endurance for the lower extremities is necessary to decrease the incidence of excessive
lumbar flexion and extension, hence lowering the risk of low back injuries due to poor
mechanics and excessive shearing forces. He also noted how racquet sport athletes tend to
asymmetrically load the trunk and shoulders and forces generated from the ball to the racquet
54
and from the court to the feet are transmitted through the core musculature and the spine. He
advocates core strength and stabilization programs will enhance awareness and control of the
trunk and spine that will in turn lower harmful static and dynamic loads.
Although, studies have previously focused on the arm and shoulder muscles during the
tennis serve, Chow, et al.
16
conducted a study focusing on the EMG analysis of the trunk muscles
(rectus abdominus, external oblique, internal oblique and lumbar erector spinae) during three
types of serves. One limitation to this study was its use of highly skilled tennis players, which
they assumed would not be generalizable. Results showed no major differences in muscle
activation pattern across all three serves. However, the abdominals were more active during the
topspin serve and bilateral differences were greater between the rectus abdominis and external
oblique as compared to the internal oblique and erector spinae muscles, hence more importance
was given to the inner core. An important finding was the consistency of co-activation of the
trunk musculature. During certain phases of serving in general, there was abdominal and low
back bilateral co-activation, which was hypothesized to help stabilize the lumbar spine during the
arch back and forward swing phases of the serve. The study concluded that abdominal and low
back exercises are important in strength and rehabilitation programs designed for tennis players,
with emphasis on eccentric training for the low back muscles.
Other studies evaluated the tennis serve in a more global perspective, specifically within
the picture of the kinetic chain. The main finding is the identification of a “feedforward” effect
of the automatic posturing that occurs prior to the serve.
31,41
The stability from the kinetic chain
acts as a torque-countertorque of diagonally related muscles in overhead athletes.
31
The body
activates the lower extremity before initiation of movement, such as with the activity of the
rectus abdominus and erector spinae before activity of the shoulder girdle.
47
Fleisig, et al.
15
55
noted the same activation patterns as they calculated kinematics of the elbow, shoulder, trunk
and knee. The activation patterns are similar to baseball pitchers and football quarterbacks,
showing that tennis athletes use principles of the reverse kinetic chain (proximal to distal) to
undergo a tennis serve, because the trunk motions proceed the upper extremity of the elbow,
wrist, and shoulder. The tennis athlete extends the knees, to move the body upward and rotates
the trunk which allows for a rotated racquet and arm.
15
Forward trunk tilt and pelvis rotation
occurs before the upper torso rotates right before ball impact.
15
This kinematic chain was found
to increase maximal linear velocity of segments from proximal (knee) to distal (racquet).
15
This
kinetic chain is different from the biomechanics of baseball pitchers, baseball batters and golfers,
who work on trunk strengthening, flexibility and coordination for rotating their upper torso
before the pelvis.
15
There are other studies
65,87
that have focused on the footwork aspect of sports in regards
to muscle activation, with attention to cutting movements, which is a staple in the game of
tennis. Stacoff, et al.
87
did a study to show the kinematic effects of different shoe sole designs
and properties on lateral stability at the ankle during sideward cutting movements. They found
that 42% (under pressure) and 30% (routine) of the time during tennis one is under a higher risk
of injuries, due to risk factors such as cutting, stopping, landing and rotating. Neptune, et al.
65
conducted a study in order to establish a database of kinematics and EMG data during cutting
movements, describe normal muscle function and coordination of selected muscles during the
cutting movements, and to identify potential muscle coordination deficiencies that may lead to
lateral ankle sprains. The study concluded that lower extremity muscles functioned similarly in
both side-shuffles and v-cut movements, the hip and knee extensor muscles functioned to
56
decelerate the center of mass during landing and propulsion during toe-off, and that there are
coupled dynamics within the lower extremity body segments.
Core Stabilization Training Programs
There is a growing popularity of stabilization exercises proposed to enhance athletic
performance and to develop muscles of the trunk.
21,31,88
Core strengthening is becoming a major
trend as well (Table B3).
31
Since “sports activity involves movement in three cardinal planes…
core musculature must be assessed and trained in these planes”.
31
However, clinical outcomes of
core strengthening programs are lacking in the research, even though core stabilization programs
are increasing.
31
Most studies are prospective, uncontrolled, case studies, with no known
randomized controlled trials.
31
There is a lack of research and evidence for the effects on
musculature and to enhance core stability.
46
However, research has determined a few variables
that are important to increasing neuromuscular control such as, joint stability exercises (joint
contraction), balance training, perturbation training (proprioceptive), plyometric exercises and
sports-specific skill training, all of which are necessary for dynamic stabilization.
31
Dynamic
stabilization exercises should improve muscular responsiveness needed to stabilize the spine
against perturbations associated with movement activity of daily living, emphasizing proper
sequencing of muscle activation, coactivating synergistic muscles, and restoring muscle strength
and endurance to key trunk stabilizers.
89
Table B3. Synonyms for Core Strengthening
31
Lumbar stabilization
Dynamic stabilization
Motor control (neuromuscular) training
Neutral spine control
Muscular fusion
Trunk Stabilization
Evidence indicates that specific patterns of muscle activation are utilized to achieve
segmental or core stabilization of the spine.
46
Commonly used exercise routines may be targeting
57
the global musculature and eliminating the local muscular system (both will increase core
stability).
46
One must be careful that there is no over activity of some muscles and underlying
activity in others.
45
Programs should entail not only trunk strengthening but also motor learning,
and muscle endurance.
31
Stabilization training has been introduced as a multifaceted program of
education, flexibility, strength, coordination, and endurance training to prevent the repetitive
micro-trauma to the spinal structures.
90
Traditional rehabilitation focuses on isolated absolute strength gains, isolated muscles,
and single planes of motion. Clark, et al.
8
proposes that all functional activities are triplanar and
require acceleration, deceleration, and dynamic stability. One plane being used leads to other
planes requiring dynamic stabilization to allow for optimal neuromuscular efficiency. One needs
to train dynamic stability to occur efficiently during all kinetic chain activities, since there is a
wide variety of movements associated with athletics, athletes need to strengthen hip and trunk
muscles that provide stability in all three planes of motion.
8,9
The biomechanical aspects of the
core are also important. Pelvic positioning, rib cage positioning, neuromuscular recruitment must
all be in a core stabilization program.
48
Core stability programs have been studied and hypothesized to improve dynamic postural
control, ensure appropriate muscular balance and joint arthrokinematics around the lumbopelvic-
hip complex, allow for the expression of dynamic functional strength, and improve
neuromuscular efficiency throughout the entire kinetic chain.
8
Mattacola and Lloyd
50
conducted
a strength and proprioception program three times a week for six weeks and found that lower
extremity exercises improved balance ability as assessed dynamically. Blackburn
49
found
strength training increased dynamic balance capabilities. A study by Blackburn, et al.
49
found
that increase proprioception and muscular strength are equally effective in promoting joint
58
stability and balance maintenance. The literature shows the need for balance research correlated
to functional athletic performance.
Most individuals inadequately train their core stabilization muscles as compared with
other muscle groups.
Many have developed muscle strength for functional activities, while few
individuals have developed muscles required for spinal stabilization.
The core, an integrated,
interdependent system, needs to be trained appropriately for efficient function during dynamic
kinetic chain activites.
If extremity muscles are strong and the core is weak, there will not be
enough force created to produce efficient movements and a weak core is a fundamental problem
of inefficient movements that leads to injury.
8
A stabilization training program is an exercise-
based approach, method for limiting and controlling movement, with muscular control as the
goal to facilitate proper movement patterns.
90
Richardson
35
has come up with the physical signs
of unwanted global muscle activity in order to aid in facilitating proper neuromuscular control.
He suggests through either observation, palpation or EMG analysis to look at aberrant movement
(i.e. posterior pelvic tilt), contours of the abdominal wall (i.e. patient unable to voluntarily relax
the abdominal wall), aberrant breathing patterns (i.e. patient unable to perform diaphragmatic
breathing pattern), and unwanted activity of the back extensors (i.e. co-activation of the thoracic
portions of the erector spinae).
There is a need to develop optimal levels of functional strength,
dynamic stability and neural adaptations, which is more important versus absolute strength
gains.
8
Reintegrating postural feed-forward and somatosensory feedback systems is important
for athletes, as will be mentioned in the next few sections.
48
Contraction of abdominals before
initiation of limb movements, which is the feedforward posture reaction, shows that voluntary
movement of the upper extremity is preceded by postural movements occurring in the lower
59
extremity (pelvis, hips and trunk) that contribute to general dynamic organization of balance and
inhibits postural disturbances.
43
Central motor program leads to sequencing of anticipatory
activity and then reduces early perturbations of the center of gravity, which is a benefit for the
athlete who needs to remain in constant postural control.
91
A dynamic core stability training
program is important in all comprehensive functional closed kinetic chain rehabilitation
programs.
8
It is important to train movements and not muscles, so that everything works
together.
33,37
Training movements integrates and improves the function of the kinetic chain,
which emphasizes the neuromuscular system which is more important versus isolated strength
gains with functional stability.
33,37
Functional training leads to the kinetic chain deceleration at
one joint and acceleration at the next joint in the chain.
33,37
Many studies
13,34,45,43,66,67,89,92,93
explored the effects of specific exercises on different
core muscles, with recent focus on exercises to restore dynamic stability to the trunk with the
findings explained here.
Callaghan et al.
92
used loading of the lumbar spine with trunk muscle
activity levels during low back extension exercises. Drysdale, et al.
67
noted that the pelvic tilt
recruits core muscles better as compared with abdominal hollowing exercises. Abdominal
hollowing and bracing were found to be greater in stabilization in abdominal and back muscles
versus posterior pelvic tilt.
45
One study by Sapsford, et al. showed that abdominal activity is a
normal response to pelvic floor muscle exercises.
66
The curl up had greater activity of the upper
rectus abdominus, while the posterior pelvic tilt had the same effect but with the lower section,
as found by Sarti, et al.
93
Norris
43
observed that lower resistance and slow movements recruits
the TVA and internal oblique better by eliminating the domination of the rectus abdominis.
Beim
et al.
13
found that the crunch produce greater muscle activation compared with sit ups and was
proportional to other modes of abdominal exercise equipment.
66
Arokoski, et al.
34
noted that
60
simple therapeutic exercises are effective in activating both abdominals and paraspinal muscles,
as limb movements and trunk positioning will increase trunk muscle activities. Richardson
45
developed a testing and exercise protocol designed to assess and improve actions of the
transverse abdominis and multifidus. This protocol consisted of relearning motor skills in ways
different from strength or endurance training because attentional focus was on correct technique
of core muscle contraction.
Swaney and Hess
18
conducted a study in order to determine effects of core stability
training in balance and posture of female collegiate swimmers versus a control group. They
followed a nine-week core stabilization-training program and used the Biodex Stability System
to measure pre- and posttest balance. Results showed that the program did effect postures but not
balance, hence a core stabilization program may improve isometric postures without effecting
dynamic stability. Lewarchik et al.
20
did a study to see if a physioball-based core stabilization
program could enhance athletic performance as measured by 4 performance tests (abdominal
endurance, velocity v-sit, vertical jump, pro agility run). The progressive physioball core strength
program included 6 exercises each with 3 levels of continuing difficulty, which was conducted 4
times a week for 7 weeks. Results showed an enhancement in performance on the tests, but there
was no significant difference versus the control. The authors concluded that this trend cannot be
contributed to the core program.
Other studies
34,56,58,46,60,70,88,92
defined affective exercises to provide a framework for
program implementation guidelines. Hyperextension of the back in the prone, standing, sitting or
while performing variations of bridging are good exercises for the lumbar paraspinal muscles as
shown by Arokoski et al
34
if performed correctly.
The side bridge was found to be the safest and
best exercise for the quadratus lumborum and the abdominal wall, with minimal spinal loading.
88
61
Konin et al.
60
suggested that ideal lumbar stabilization can occur during an exercise when there is
voluntary activation of the transverse abdominnis with proper breathing. Sherry et al.
94
in his
study found that a hamstring rehabilitation program incorporating core stabilization was
beneficial in subjects with chronic hip adductor pain. McGill, et al.
88
conducted a study with an
objective to collect isometric endurance times for low back stabilization and found that there
were differences in endurance times between males and females and that endurance times are a
good indicator for clinical rehabilitation protocols. Responses from the lumbar multifidus and
abdominal muscles during leg movement was evaluated by Hodges, et al. who concluded that the
CNS activates the abdominal muscles and the multifidus for stabilization purposes before limb
movements take place, with the TVA and the obliques firing in no relation to the force direction
or magnitude.
58
Arokoski, et al.
34
did a study whose objective was to assess paraspinal and
abdominal muscle activities during different therapeutic exercises and to study how limb
movements and trunk positions affect this. Arokoski
34
found that simple traditional therapeutic
exercises for low back pain (i.e. bridging and extension in prone) were effective in recruiting
these muscles, along with variations in body positioning and balance and that women were able
to activate these muscles easier and more effectively as compared with men. Johnson
46
did a
research study involving both normal and low back pain patients using EMG and biomechanical
analysis, showing that an exercise program emphasizing local muscle function (constant
isometric contraction of the transverse abdominus and multifidus during trunk exercises) may be
beneficial for controlling the trunk and providing core stabilization. Muscle strengthening
therapy increases spinal stabilization.
70
Studies have shown pelvic stabilization for training
lumbar extensor muscles are important and that strengthening of the back, legs, and abdominals
62
leads to increase muscle stabilization.
56
Core training programs have been used in the
rehabilitation of hip musculature as well.
94
Some studies have shown either a lack of evidence or poor results for certain exercises,
such as with the prone superman, sit ups with bent knees, the pelvic tilt and issues of flexibility
affecting the core.
73,92
Universally, there was found to be no single exercise to challenge all the
flexor or extensor muscles at the same time, indicating the need for several exercises.
73
Exercises
posing a motor learning challenge to some subjects, should be an important consideration as
well, for there is a progression of motor learning that should be followed (Figure B1).
89
Retraining core stability requires cognitive input encompassing slow and deliberate patterns until
new patterns are learned.
54
Optimal movement patterns for extremity mobility with the core
remaining stable is a process requiring motor relearning for reorganization of recruitment
patterns from the CNS.
54
With minor discrepancies within exercises as previously mentioned (i.e. abdominal
exercises), the majority of the findings seem to suggest a similar pattern. Overall, the exercises
for all parts of the core need to concentrate on motor control, emphasizing the neutral spine
posture, and contraction of the pelvic floor muscles and the TVA with the multifidus. The
exercises should be conducted under low level tonic contractions and progress to co-contraction
of the whole core with functional tasks gradually incorporated.
63
Figure B1. The Elements of Relearning a Motor Skill
46
Relearning the motor skill of deep muscle co-contraction
Increase activation of the Decrease unwanted overactivity of the
Local musculature global muscles
Improve the perception of the skill
Improve precision of the skill
Repeated practice of the skill
Progression to functional upright tasks
Since there is no universally accepted standard program for core stabilization, it is not
known what type, frequency or duration of exercises should be prescribed.
34
There are proposed
guidelines such as with Robinson
90
saying that muscular control of the core muscles should be
the goal of the stabilization training program. There are suggestions in the literature stressing the
importance of concepts such as, functional training, skills transferring more effectively when
practicing complex skills in entirety rather than in isolation, and exercises should be systematic,
progressive, functional, include concentric, eccentric, and isometric contractions.
8,33,37,40,
Panjabi
provided a model of how stabilization is achieved. He says there are three interdependent
subsystems, passive (osseous and articular strucuters, spinal ligaments), active (force generating
capacity of the muscles), and the neural control subsystem (control of these muscles to provide
spinal support), which should be the focus.
6,46
Sall
95
has even emphasized that abdominal
64
strengthening is the cornerstone of the stabilization program.
95
Gambetta has suggested that the
more functional the environments are in the training, the more versatile the athlete will be in
handling the forces and stresses incurred by the actual sport activity.
33,37
Thus, there is a need to
train, test, and rehabilitate balance in motion not in stillness.
83
King
48
recommends a 4 step
approach (static postural reeducation for motor learning, lower core dynamic stability, upper core
dynamic stability, and posterior core stability-trunk extensors). For example one may go through
abdominal hollowing exercises to a progression of upper or lower extremity movement during
abdominal hollowing, and once those levels are mastered extension exercises are incorporated.
Jeffreys
21
has encompassed the majority of the research findings as he created a
progressive core stability program of five levels. The purpose is to start by working on mastery
of the core contraction in order to facilitate neuromuscular re-programming, then for muscular
adaptation the static holds can be joined by slow movements in a stable environment. As the
athlete adapts to being able to control their core musculature in an appropriate manner under
these minimal stress conditions, the next three levels (static holds in unstable environment and
dynamic movement in a stable environment, dynamic movements in an unstable environment,
and resisted dynamic movement in an unstable environment) will add an increasing level of
difficulty which will lead the athlete to be able to use their core efficiently in sport specific skills,
which is always the main expected goal with functional sport rehabilitation programs.
Summary
The muscular system of the core can be organized into a global and inner compartment.
Although there is a meager amount of information on standardized programs, optimum function
of the core muscles has been found to be dependent on proper proprioceptive neuromuscular
65
facilitation, which may be enhanced through core stabilization training, focusing on correct
biomechanical postural alignment and muscle coactivation. The literature suggests a pattern for
training programs (exercises for all parts of the core need to concentrate on motor control,
emphasizing the neutral spine posture, and contraction of the pelvic floor muscles and the TVA
with the multifidus) and Jeffreys
21
has proposed a five-step approach. The sport of tennis
necessitates athlete movement in a multiplanar manner with dynamic balance and transfers force
through the kinetic chain during tennis racquet swings. Dynamic balance is one positive outcome
from enhancing core stabilization and can be measured indirectly through the SEBT.
66
APPENDIX C
ADDITIONAL METHODS
Table C1. Informed Consent Form
The Effects of a Six-Week Core Stabilization-
Training Program on Dynamic Balance
in Tennis Athletes
Introduction
I, ____________________, have been asked to participate in this research study which has been
explained to me by Kimberly M. Samson, BS, ATC. This research is being conducted by
Kimberly M. Samson, BS, ATC under the supervision of Michelle A. Sandrey, PhD, ATC to
fulfill the requirements for a master’s thesis in Athletic Training in the School of Physical
Education at West Virginia University.
Purpose of the Study
I understand that the purpose of this study is to assess the outcome of a core (trunk of the body)
stabilization-training program (exercises for abdomen, low back and pelvis using body weight,
medicine balls, and Swiss Balls) on dynamic balance. Medicine balls are weighted, rubber
coated and handheld, while Swiss Balls are air filled and rubber coated.
Description of Procedures
This study will be conducted at the Athletic Training Clinic Laboratory and Old Gym at
Waynesburg College, Waynesburg, PA 15370.
This informed consent form explains my rights as a research subject. I will be shown and
voluntarily fill out an injury history and demographic questionnaire after my consent is obtained,
which will be kept confidential. I do not have to answer all questions.
If I am chosen for this study I will undergo a pre and post test measurement of my dynamic
balance using the Star Excursion Balance Test (SEBT). The test will be conducted one week
prior to and following the six-week exercise protocol. The SEBT involves a taped star pattern
with 8 projections (excursions) each at 45 degrees from each other, on an even floor surface. I
will place my non-dominant foot on the middle of the star pattern, while my dominant foot will
be reaching as far as possible in each of the 8 excursions. A practice session of 6 times in each
excursion followed by a one minute rest and then the measured average in inches of three trials
will be included in the research data. Trials only count if I am able to maintain balance
throughout each excursion. Trials will be discarded and repeated if the reach foot is used to
provide considerable support when touching the ground, the stance foot is lifted from the center
of the star grid or if the subject is unable to maintain balance throughout each excursion.
67
The Effects of a Six-Week Core Stabilization-Training Program on
Dynamic Balance in Tennis Athletes
The six- week protocol for the core stabilization-training program will be conducted as follows. I
will follow the program 3 times a week for an average of 15-30 minute sessions. There will be 3
progressive levels of exercises focusing on strengthening the abdominal, low back and pelvic
muscles while maintaining neuromuscular control. The exercises involve bending at the trunk in
a sit-up like manner as well as bending backwards, at the sides, and rotating. I will start at level
one and progress through each level according to the protocol for that particular day.
Risk and Discomforts
I understand that there are no known or expected risks from participating in this study. Mild
muscle soreness and the possibility of losing my balance are the only known or expected
discomforts with performing the Star Excursion Balance Test (SEBT) and core stabilization
exercises. While performing the SEBT, it is likely that I will not lose my balance because I will
be performing the test with my eyes open and the principle examiner will be standing next to me.
I understand that every precaution has been taken to prevent me from being injured in this study.
If an adverse physical or psychological reaction were to occur during any point of the study,
appropriate care or referral will be made available. Should any injury occur, I understand that
Kimberly M. Samson, BS, ATC will provide first aid and make any necessary medical referral.
Alternative
I understand that I do not have to participate in this study.
Benefits
I understand that this study may not be of direct benefit to me, but the knowledge gained may be
of benefit to others.
Contact Persons
For more information about this research, I can contact Kimberly M. Samson, BS, ATC at (724)
852-3446 or at [email protected] or her faculty advisor, Michelle A.
Sandrey, PhD, ATC at (304) 293-3295 Ext. 5220 or at [email protected]. For information
regarding my rights as a research subject, I may contact the Professional Development
Committee Chair at Waynesburg College through Mr. AJ Anglin at (724) 852-3253.
68
The Effects of a Six-Week Core Stabilization-Training Program on
Dynamic Balance in Tennis Athletes
Confidentiality
I understand that any information about me as a result of my participation in this research will be
kept confidential as legally possible. Identifying information on the informed consent form and
demographic/injury history questionnaire will be kept confidential by an assigned code number
to each informed consent form and demographic/injury history
questionnaire. I understand that my research records and test results, just like hospital records,
may be subpoenaed by court order without my additional consent. In any publications or
presentations that result from this research, neither my name nor any information from which I
might be identified will be used without my consent.
Voluntary Participation
Participation in this study is voluntary. I understand that I am free to refuse or withdraw my
consent to participate at any point in this study and this will involve no penalty or loss of benefits
to which I am entitled to as a student athlete at Waynesburg College, that grades and class
standing will not be affected, and that status on the tennis team will not be affected. Treatment
and evaluation of injuries will also not be affected. I have been given the opportunity to ask
questions about the research, and I have received answers concerning areas that I did not
understand. In the event new information becomes available that may affect my willingness to
continue to participate in this study, this information will be given to me so I may make an
informed decision about my participation.
Upon signing this form, I will receive a copy.
I willingly consent to participate in this research.
___________________________________ __________ __________
Signature of Subject or Legal Representative Date Time
___________________________________ __________ __________
Signature of Principle Investigator
69
Table C2. Informed Consent Form for Control
The Effects of a Six-Week Core Stabilization-
Training Program on Dynamic Balance
in Tennis Athletes
Introduction
I, ____________________, have been asked to participate in this research study which has been
explained to me by Kimberly M. Samson, BS, ATC. This research is being conducted by
Kimberly M. Samson, BS, ATC under the supervision of Michelle A. Sandrey, PhD, ATC to
fulfill the requirements for a master’s thesis in Athletic Training in the School of Physical
Education at West Virginia University.
Purpose of the Study
I understand that the purpose of this study is to assess the outcome of a core (trunk of the body)
stabilization-training program (exercises for abdomen, low back and pelvis using body weight,
medicine balls, and Swiss Balls) on dynamic balance. Medicine balls are weighted, rubber
coated and handheld, while Swiss Balls are air filled and rubber coated.
Description of Procedures
This study will be conducted at the Athletic Training Clinic Laboratory and Old Gym at
Waynesburg College, Waynesburg, PA 15370.
This informed consent form explains my rights as a research subject. I will be shown and
voluntarily fill out an injury history and demographic questionnaire after my consent is obtained,
which will be kept confidential. I do not have to answer all questions.
If I am chosen for this study I will undergo a pre and post test measurement of my dynamic
balance using the Star Excursion Balance Test (SEBT). The test will be conducted one week
prior to and following the six-week exercise protocol. The SEBT involves a taped star pattern
with 8 projections (excursions) each at 45 degrees from each other, on an even floor surface. I
will place my non-dominant foot on the middle of the star pattern, while my dominant foot will
be reaching as far as possible in each of the 8 excursions. A practice session of 6 times in each
excursion followed by a one minute rest and then the measured average in inches of three trials
will be included in the research data. Trials only count if I am able to maintain balance
throughout each excursion. Trials will be discarded and repeated if the reach foot is used to
provide considerable support when touching the ground, the stance foot is lifted from the center
of the star grid or if the subject is unable to maintain balance throughout each excursion.
70
The Effects of a Six-Week Core Stabilization-Training Program on
Dynamic Balance in Tennis Athletes
If I am chosen for the control group I will not perform any of the core stabilization training
exercises. I will be explained the guidelines of this group, and will be contacted on a weekly
basis and will be asked to answer all questions accurately and honestly.
Risk and Discomforts
I understand that there are no known or expected risks from participating in this study. Mild
muscle soreness and the possibility of losing my balance are the only known or expected
discomforts with performing the Star Excursion Balance Test (SEBT) and core stabilization
exercises. While performing the SEBT, it is likely that I will not lose my balance because I will
be performing the test with my eyes open and the principle examiner will be standing next to me.
I understand that every precaution has been taken to prevent me from being injured in this study.
If an adverse physical or psychological reaction were to occur during any point of the study,
appropriate care or referral will be made available. Should any injury occur, I understand that
Kimberly M. Samson, BS, ATC will provide first aid and make any necessary medical referral.
Alternative
I understand that I do not have to participate in this study.
Benefits
I understand that this study may not be of direct benefit to me, but the knowledge gained may be
of benefit to others.
Contact Persons
For more information about this research, I can contact Kimberly M. Samson, BS, ATC at (724)
852-3446 or at [email protected] or her faculty advisor, Michelle A. Sandrey, PhD,
ATC at (304) 293-3295 Ext. 5220 or at [email protected]. For information regarding my
rights as a research subject, I may contact the Professional Development Committee Chair at
Waynesburg College through Mr. AJ Anglin at (724) 852-3253.
71
The Effects of a Six-Week Core Stabilization-Training Program on
Dynamic Balance in Tennis Athletes
Confidentiality
I understand that any information about me as a result of my participation in this research will be
kept confidential as legally possible. Identifying information on the informed consent form and
demographic/injury history questionnaire will be kept confidential by an assigned code number
to each informed consent form and demographic/injury history
questionnaire. I understand that my research records and test results, just like hospital records,
may be subpoenaed by court order without my additional consent. In any publications or
presentations that result from this research, neither my name nor any information from which I
might be identified will be used without my consent.
Voluntary Participation
Participation in this study is voluntary. I understand that I am free to refuse or withdraw my
consent to participate at any point in this study and this will involve no penalty or loss of benefits
to which I am entitled to as a student or student athlete at Waynesburg College or West Virginia
University, that grades and class standing will not be affected, and that academic status will not
be affected. Treatment and evaluation of injuries will also not be affected. I have been given the
opportunity to ask questions about the research, and I have received answers concerning areas
that I did not understand. In the event new information becomes available that may affect my
willingness to continue to participate in this study, this information will be given to me so I may
make an informed decision about my participation.
Upon signing this form, I will receive a copy.
I willingly consent to participate in this research.
___________________________________ __________ __________
Signature of Subject or Legal Representative Date Time
___________________________________ __________ __________
Signature of Principle Investigator
72
Table C3. Demographic/Injury History Questionnaire
Demographic/Injury History Questionnaire
Demographics
Name:
Age:
Gender:
Height:
Weight:
Year in School: Freshman/Sophomore/Junior/Senior/Graduate Student
Season with Waynesburg College tennis team: 1
st
/2
nd
/3
rd
/4
th
/5
th
/6
th
/Medical Red Shirt
Injury History
1. Have you had a lower extremity injury within the past six months that required the
intervention of a medical or allied health care professional? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
2. Have you had an upper extremity injury within the past six months that required the
intervention of a medical or allied health care professional? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
3. Have you had a head injury within the past six months that required the intervention of a
medical or allied health care professional? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
4. Have you had any neurological disorders within the past six months that required the
intervention of a medical or allied health care professional? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
5. Have you had any vestibular disorders within the past six months that required the intervention
of a medical or allied health care professional? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
73
6. Have you had any visual disorders within the past six months that required the intervention of
a medical or allied health care professional? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
7. Are you currently taking any medications that might affect your ability to balance? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
8. Have you completed or currently following a rehabilitation program for core stability within
the past six months? Yes/No
If yes, please explain:
______________________________________________________________________________
______________________________________________________________________________
9. Are you currently participating on the Waynesburg College men’s or women’s tennis
teams? Yes/No
10. Are you currently involved in any other physical activity (i.e. weight lifting, aerobics,
another sport) besides tennis? Yes/No
If yes, please explain what other physical activities you are involved in and how often you
participate in each activity:
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
74
Figure C1. Star Excursion Balance Test for a Right Limb Stance
19
Abbreviations: A: anterior excursion; AM: anteromedial excursion; M: medial excursion;
PM: posteromedial excursion; P: posterior excursion; PL: posterolateral excursion; L:
lateral excursion; AL: anterolateral excursion.
75
Figure C2. Star Excursion Balance Test for a Left Limb Stance
19
Abbreviations: A: anterior excursion; AM: anteromedial excursion; M: medial excursion;
PM: posteromedial excursion; P: posterior excursion; PL: posterolateral excursion; L:
lateral excursion; AL: anterolateral excursion.
76
Figure C3. Core Stabilization-Training Program Exercises: Level 1
Level 1:Week 1
Day 1-3:Abdominal Muscle Contraction. Athlete will lie in a supine position (on their back)
with knees bent to a range where their feet lie on the floor. They will then be instructed to
contract their abdominals, drawing in their navel toward the floor without rotating the
pelvis backwards. 3x20
Abdominal Muscle Contraction. Athlete will get in a quadruped position (on hands and
knees) and will be instructed to contract their abdominals, drawing in their bellybutton
toward the ceiling without rotating their pelvis backwards. 2x15
77
Abdominal Muscle Contraction. Athlete will support themselves in a sideways posture
with their right forearm and right foot on the floor. Athlete will be instructed to maintain
a straight alignment while contracting the right oblique muscle. The same will be
repeated for the left side. 1x6/each side (10sec holds)
Level 1:Week 2
Day 4-6: Abdominal Muscle Contraction 1x20
Dying Bug. Athlete will lie in a supine position with upper and lower extremities
facing straight toward the ceiling. Athlete will be instructed to maintain an abdominal
contraction while simultaneously moving their extremities toward the torso in slow
controlled movements. 3x20
78
Bridging. Athlete will get in a quadruped position and be instructed to contract their
abdominals while simultaneously extending one leg back as straight as possible in
a slow controlled manner, and then bringing that leg back to original starting position.
The movement will continue for the opposite leg. 3x15
Seated Medicine Ball Rotation. Athlete will sit upright on the floor with knees bent up
to 45 degrees. The athlete will have a medicine ball held with both hands and will be
instructed to rotate their upper torso with the arms extended while holding the medicine
ball and maintaining abdominal contraction. 3x15
79
Figure C4. Core Stabilization-Training Program Exercises: Level 2
Level 2:Week 3
Day 1-3: Abdominal Muscle Contraction 1x20
Seated on Swiss Ball. Athlete will sit on a proper size Swiss Ball in an upright posture
and will be instructed to contract their abdominals without rotating their pelvis backwards
and staying balanced on the Swiss Ball. 3x20
Squat with Swiss Ball. Athlete will be in a squat position with a Swiss Ball between the
middle of their back and a wall. Athlete will be instructed to maintain a proper squatting
posture while contracting their abdominals during a squat. 3x15
80
Superman. Athlete will lie on their stomach with the upper and lower extremities
positioned straight out and fully extended. Athlete will be instructed to raise both
extremities at the same time not to exceed the onset of extreme low back arching. Both
extremities will return to their original starting positions in a controlled manner. 3x15
Level 2:Week 4
Day 4-6: Abdominal Muscle Contraction 1x20
Multidirectional Lunge. Athlete will stand in upright posture with both hands on their
hip. Athlete will then do a lunge with their right knee and hip flexed to 90 degrees and
their left knee flexed to 90 degrees, with their left hip at 180 degrees. The lunge will be
directed straight ahead and after going back to the original starting position, the lunge
will be repeated with similar posture 45 degrees to the right. The same movement will be
conducted for the left leg. 3x15
81
Oblique Pulley with Side Shuffles. Athlete will partner up with another athlete. One
athlete will be instructed to maintain the hold of a therapeutic resistance band and remain
stationary, while the other athlete holds the other end with both hands in an extended
position. The non-stationary athlete will do side shuffles to the point of minimal
resistance and will then pull horizontally toward the non-stationary side, afterwards the
athlete will side shuffle back to the original starting position. The athlete will do the same
actions but face the other direction and both athletes will switch roles. 3x15
Standing Wall Cross Toss. The athlete will stand upright facing a solid wall a couple of
feet away while holding a medicine ball with both hands at waist level. The athlete will
turn their shoulders to the left and then toss the ball at the wall in a right diagonal
direction and immediately turn to the right and catch the ball while maintaining a
contracted torso. The actions will take place in the opposite direction. 3x20
82
Figure C5. Core Stabilization-Training Program Exercises: Level 3
Level 3:Week 5
Day 1-3: Abdominal Muscle Contraction 1x20
Diagonal Curls on Swiss Ball. Athlete will have both feet planted on the floor while
their upper back is supported on a Swiss Ball and their arms are crossed over their chest.
The athlete will be instructed to raise their upper body using their trunk muscles and turn
toward an opposite knee, afterwards the upper body is returned to the original starting
position in a controlled manner. The same action will be repeated toward the opposite
knee. 3x10
Twists on Swiss Ball. Athlete will have both feet planted on the floor while their
upper back is supported on a Swiss Ball and their arms are extended toward the ceiling
over their chest, holding a medicine ball. The athlete will then maintain stabilization of
their lower body while moving their extended arms at the same time to one side of the
body, and then back to the original starting position, where they will do the same action
but to the opposite side. 3x15
83
Standing with Tennis Racquet on an Unstable Surface. Athlete will hold a tennis
racquet in their dominant hand while standing on one leg. The athlete will then be
instructed to do forehand and backhand swings while maintaining balance. The same
actions will be conducted on the opposite leg. 4x10
84
Table C4. Core Stabilization-Training Program Protocol
Week 1 to Week 5
Specific prescribed sets and repetitions will be performed for each particular exercise with a one-
minute rest between sets.
Subjects will progress to the next level of the core stabilization-training program according to the
exercise protocol for that day.
85
Table C5. Dynamic Balance Test using the Star Excursion Balance Test (Pre-Test &
Post-Test)
1. Subjects will be instructed to stand in the center of the star grid and maintain a
single-leg stance while reaching with the opposite leg to touch as far as possible
along a chosen excursion.
2. Subjects will be instructed to touch the farthest point possible as light as possible
along a chosen excursion with the most distal part of their reach foot.
3. Subjects were instructed to return to a bilateral stance while maintaining their
balance.
4. Subjects were instructed to perform six practice trials in each of the eight
excursions with a 10-second rest between each excursion.
5. After a one-minute rest following the last practice trial, testing began.
6. Three trials were performed in each of the eight excursions with a 10-second rest
between each excursion.
7. Trials were discarded and repeated if the reach foot was used to provide
considerable support when touching the ground, if the subjects’ stance foot was
lifted from the center of the star grid, or if the subjects were not able to maintain
their balance at any point in the trial.
8. The average scores for each excursion were recorded as the subjects’ dynamic
balance score.
86
Table C6. Pre-Test Data Collection Sheet for the Star Excursion Balance test
Pre-Test Data Collection Sheet for the Star Excursion Balance test
Code: ___________________________________
Age: _____________________________________
Gender: __________________________________
Height: ___________________________________
Weight: ___________________________________
Right Leg Length: ___________________________
Left Leg Length:_____________________________
Dominant Lower Extremity: Right/Left
Excursion Trial 1 Trial 2 Trial 3 Average
Anterior
Anteromedial
Medial
Posteromedial
Posterior
Posterolateral
Lateral
Anterolateral
87
Table C7. Post-Test Data Collection Sheet for the Star Excursion Balance test
Post-Test Data Collection Sheet for the Star Excursion Balance test
Code: ___________________________________
Age: _____________________________________
Gender: __________________________________
Height: ___________________________________
Weight: ___________________________________
Right Leg Length: ___________________________
Left Leg Length:_____________________________
Dominant Lower Extremity: Right/Left
Excursion Trial 1 Trial 2 Trial 3 Average
Anterior
Anteromedial
Medial
Posteromedial
Posterior
Posterolateral
Lateral
Anterolateral
88
Table C8. Jeffreys Progressive Core Stability Program
21
Classification Characteristic Example
Mastery of core contraction Static Isometric contraction Side bridge
Static holds and slow Static isometric contraction with controlled Dead bug
movements in stable simultaneous limb movement
environment
Static holds in unstable Static isometric contraction on Abdominal isometric
environment and dynamic a unbalanced surface/body movement contraction on
movement in a stable on a static surface Swissball
environment
Dynamic movements in Body movement on an unbalanced Trunk twists on
an unstable environment surface Swissball
Resisted dynamic Resisted body movement on an Trunk twists with
movement in unstable unbalanced surface Theraband on
environment Swissball
89
Table C9. Tests of Balance
19
Static Tests
Dynamic Tests
Straight leg stance
Functional reach
Romberg
Figure 8
Tandem Romberg
Gait (via video)
Standing force plate measures
Jumping from one surface to another
Vertical jump
Balance board
90
APPENDIX D
ADDITIONAL RESULTS
Table D1. Descriptive Statistics for the Subjects (n=28)
Mean
+
Age
20.18
1.02
Height (cm)
171.31
9.57
Mass (kg)
69.92
15.32
91
Table D2. Descriptive Statistics for the Experimental Group and Control Group (n=28)
Core Stabilization-Training
Group
Control Group
Males
6
5
Females
7
10
92
Table D3. Descriptive Statistics for the Pre-Test Data for the Star Excursion Balance Test (n=28)
Group
Mean
+
N
PRE-TEST
EXCURSION
Anterior
Core
94.16
8.34
13
Control
88.71
7.00
15
Anteromedial
Core
95.88
8.64
13
Control
91.28
7.72
15
Medial
Core
97.99
7.57
13
Control
94.37
7.45
15
Posteromedial
Core
100.03
7.74
13
Control
98.7
8.35
15
Posterior
Core
100.62
7.46
13
Control
99.16
9.74
15
Posterolateral
Core
93.25
9.08
13
Control
91.66
8.85
15
Lateral
Core
85.31
11.15
13
Control
78.33
13.61
15
Anterolateral
Core
82.99
10.52
13
Control
78.90
6.00
15
93
Table D4. Descriptive Statistics for the Post-Test Data for the Star Excursion Balance Test
(n=28)
Group
Mean
+
N
POST-TEST
EXCURSION
Anterior
Core
99.08
11.50
13
Control
90.62
7.38
15
Anteromedial
Core
102.18
10.47
13
Control
93.88
7.25
15
Medial
Core
106.70
10.15
13
Control
97.56
9.21
15
Posteromedial
Core
110.99
9.81
13
Control
103.17
9.77
15
Posterior
Core
110.77
8.59
13
Control
102.02
10.47
15
Posterolateral
Core
102.38
9.49
13
Control
94.26
9.94
15
Lateral
Core
91.42
10.06
13
Control
84.20
8.24
15
Anterolateral
Core
86.86
9.53
13
Control
82.19
6.91
15
94
Table D5. One-Way ANOVA for the Pre-Test Data for the Star Excursion Balance Test (n=28)
df
F
P Value
ES
PRE-TEST
EXCURSION
Anterior
1,26
3.527
.072
.275
Anteromedial
1,26
2.216
.149
.332
Medial
1,26
1.623
.214
.421
Posteromedial
1,26
.189
.667
.614
Posterior
1,26
.192
.665
.490
Posterolateral
1,26
.219
.643
.506
Lateral
1,26
2.162
.153
.340
Anterolateral
1,26
1.652
.210
.421
* Significance at the .05 level (P<.05)
95
Table D6. Main Effects and Interactions for Time, Group, and Time X Group for the Star
Excursion Balance Test (n=28)
Excursion
df
F
P Value
ES
TIME
Anterior
1,26
9.840
.004
.275
Anteromedial
1,26
12.935
.001
.332
Medial
1,26
18.904
.000
.421
Posteromedial
1,26
41.440
.000
.614
Posterior
1,26
25.020
.000
.490
Posterolateral
1,26
26.599
.000
.506
Lateral
1,26
13.395
.001
.340
Anterolateral
1,26
18.872
.000
.421
GROUP
Anterior
1,26
5.084
.033
.164
Anteromedial
1,26
4.672
.040
.152
Medial
1,26
4.591
.042
.150
Posteromedial
1,26
2.064
.163
.074
Posterior
1,26
2.477
.128
.087
Posterolateral
1,26
2.094
.160
.075
Lateral
1,26
3.461
.074
.117
Anterolateral
1,26
2.077
.161
.074
TIME X
GROUP
Anterior
1,26
1.920
.178
.069
Anteromedial
1,26
2.234
.147
.079
Medial
1,26
4.057
.054
.135
Posteromedial
1,26
7.310
.012
.219
Posterior
1,26
7.854
.009
.232
Posterolateral
1,26
8.260
.008
.241
Lateral
1,26
.005
.942
.000
Anterolateral
1,26
.125
.726
.005
* Significance at the .00625 level (P<.00625)
96
APPENDIX E
RECOMMENDATIONS FOR FUTURE RESEARCH
1. Since there is no set protocol for the duration of a core stabilization training program, use
a variable workout schedule by evaluating training programs of 6 weeks, 9 weeks and 12
weeks or longer in duration.
2. Increase the number of subjects from 13-15 per group to at least 20 per group.
3. Conduct the study with subjects that are not involved in physical activity.
4. Conduct the study with injured subjects or subjects that have a history of vestibular or
neurological disorders with an athletic and non-athletic population.
5. Decrease the number of subjects per core stabilization –training sessions to 5 or less.
6. Conduct a study that examines the effects of various core stabilization-training programs
(anterior core, posterior core, and combined anterior/posterior core) on dynamic balance.
7. Conduct the study with a control group consisting of tennis athletes.
8. Conduct the study with other means to assess the effectiveness of a core stabilization-
training program (i.e. EMG analysis, agility tests, static balance, etc).
9. Conduct the study with more sport specific populations with functional core programs
related to their sport.
10. Conduct the study to assess injury rates pre and post core stabilization-training program.
11. Conduct the study to assess endurance of the core musculature and of overall whole body
fatigue pre and post core stabilization-training program.
97
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