The Effects of a Five-Week Core Stabilization-Training Programon Dynamic Balance in Tennis Athletes

Kimberly M. Samson, BS, ATC, PES

Thesis submitted to theSchool of Physical Educationat West Virginia University

in partial fulfillment of the requirementsfor the degree of

Master of Sciencein

Athletic Training

Michelle A. Sandrey, PhD, ATC, ChairRuth Kershner, RN, CHES, EdD

Allison Hetrick, MEd, ATC, CSCS

School of Physical Education

Morgantown, WV

2005

Key Words: Proprioception, Neuromuscular Control, Balance, Core

ABSTRACT

The Effects of a Five-Week Core Stabilization-Training Programon 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 anddynamic balance. Core stabilization and dynamic balance are important components to the sportof 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 experimentaland control group. This study included 13 healthy physically active collegiate level tennisathletes and 15 subjects in the control group of aged matched activity cohorts.The five-weekprotocol for the core stabilization-training program was conducted as follows: subjects followedthe program 3 times a week for an average of 30-minute sessions. There were 3 progressivelevels 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 dynamicbalance using the Star Excursion Balance Test (SEBT). The test was conducted one week priorto and following the five-week exercise protocol. No significant difference was found for pre-testresults for all excursions. A significant difference for time was found for pre-test and post-testwithin subjects for all eight excursions (anterior, anteromedial, medial, posteromedial, posterior,posterolateral, lateral, anterolateral). There were no significant main effects for Group orinteraction between Time and Group. In conclusion, Core stabilization-training may be used toenhance dynamic balance in tennis athletes.

iii

ACKNOWLEDGEMENTS

I would like to thank my family, especially Mom, Dad, Jimbo, and Marta, for theirunconditional love and support throughout my journey in higher education. No words or materialpossessions 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 aswell as graduate school. You have been there for me and are a huge part of who I am and where Iam today.

I would like to thank Ruth Kershner, RN, CHES, EdD and Allison Hetrick, MEd, ATC, CSCSfor being on my committee and for all of your help during this past year. I greatly enjoyedworking with you and learning from you. I greatly appreciate the time you had to sacrifice out ofyour schedules to guide me through this process.

I would like to thank all of the undergraduate students at Waynesburg College whoparticipated and completed this study. It is a wonderful feeling to know that you all took effortsto support this project in order to see me succeed. It has been a pleasure working with youthroughout 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 thisresearch topic possible. I cannot thank you enough for everything that you have been for thisstudy. You helped me to have faith in this topic, was all ‘open arms’ about participating, helpedwith 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 Iwould 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 agreat source of support and encouragement. Special thank you to Lee Floyd for taking all theexercise photographs and help with technical support.

A special thank you to Dr. Michelle A. Sandrey for giving me the opportunity to be a partof the graduate athletic training program at West Virginia University and a graduateassistant athletic trainer at Waynesburg College. You are an unsung hero of mentoring. Youhelped me in all aspects of this project from the initial steps of brainstorming, to conducting thestudy and then to putting it all on paper. You gave this project many elements that no one couldhave 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.

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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 Panjabi6 (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 known15,16,17 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 Hess18 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.

Piegaro19 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. Jeffreys21 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 Jeffreys21 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 Armstrong23 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 Earl26, 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 Armstrong23 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 (ICC2,1 = .67-.87) and (ICC2,1 = .81-.96),

respectively.

Gribble24 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. Raty30 and

Olmsted28 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 Armstrong23 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.

Olmsted28 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.

Gribble24 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

Hertel27 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 studies5,17,21,32,33,34,35,36,37, thus

the exercise protocol to be used in this study was derived from those sources, specifically

Jeffreys21 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 McGill38

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. Brandon32

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 times29 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 (F1,26= 9.840, P= .004, ES= .275), anteromedial excursion (F1,26= 12.935, P= .001,

ES= .332), medial excursion (F1,26= 18.904, P= .000, ES= .421), posteromedial excursion (F1,26=

41.440, P= .000, ES= .614), posterior excursion (F1,26= 25.020, P= .000, ES= .490),

posterolateral excursion (F1,26= 26.599, P= .000, ES= .506), lateral excursion (F1,26= 13.395, P=

.001, ES= .340), and anterolateral excursion (F1,26= 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 Hertel26 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 Hertel26 may provide answers to the importance of balance strategies in

tennis. Earl and Hertel26 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 study19 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 Hess18 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 Piegaro19 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 Hess18 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 Piegaro19 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 Hess18 did a nine-week program, and Lewrchick20 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, Piegaro19 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 Hess18 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

Bouisset9 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 Richardson9 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. Richardson45 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 Guskiewicz49 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). Mattacola50 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. Richardson35 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 study27.

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

REFERENCES

1. Clark M. Essentials of integrated training part 5: core stabilization training.www.ptonthenet.com. 1998.

2. Aaron G. The use of stabilization Training in the rehabilitation of the athlete. SportsPhysical Therapy Home Study Course. 1996.

3. Dominguez RH. Total body training. Moving Force Systems. East Dundee, IL.1982.

4. Gracovetsky S, Farfan H. The optimum spine. Spine. 1986;11:543-573.

5. Gracovetsky S, Farfan H, Hueller C. The abdominal mechanism. Spine.1985;10:317-324.

6. Panjabi MM. The stabilizing system of the spine. Part I: function, dysfunction,adaptation, and enhancement. J Spinal Disord. 1992;5:383-389.

7. Panjabi MM, Tech D. White AA. Basic biomechanics of the spine. Neurosurgery.1980;7:76-93.

8. Clark MA, Fater D, Reuteman P. Core (trunk) stabilization and its importance for closed kinetic chain rehabilitation. Orthop Phys Ther Clin North Am. 2000;9:119-135.

9. Leetun DT. Core stability measures as risk factors for lower extremity injury in athletes.Med Sci Sports Exerc. 2004;36:926-34.

10. O’Sullivan PB, Twomey LT, Allison GT. Evaluation of specific stabilizing exercise inthe treatment of chronic low back pain with radiologic diagnosis of spondylolysis or

spondylolisthesis. Spine. 1999;22:2959-2967.

11. Shaffer A. Hard core. Tennis. 2001;37:112-114.

12. Roetert EP. Balance point. Tennis. 2002;38:48-50.

13. Beim G, Giraldo JL, Pincivero DM, Borror MJ, FU FH. Abdominal strengtheningexercises: a comparative EMG study. J Sport Rehabil. 1997;6:11-20.

14. Roetert P, Ellenbecker TS. Complete Conditioning for Tennis. Human Kinetics.1998: 62-64.

15. Fleisig G, Nicholls R, Elliott B, Escamilla R. Kinematics used by world class tennisplayers to produce high-velocity serves. Sports Biomech. 2003;2:51-71.

25

16. Chow JW, Shim JH, Lim YT. Lower trunk muscle activity during the tennis serve. J SciMed Sport. 2003;6:512-8.

17. Liemohn W. Exercise Prescription and the back. New York: McGraw-Hill MedicalPublishing Division. 2001.

18. Swaney MR, Hess RA. The effects of core stabilization on balance and posture in femalecollegiate 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, MorgantownWV: West Virginia University. 2003.

20. Lewarchik TM, Bechtel ME, Bradley DM, Hughes CJ, Smith TD. The effects of a sevenweek core stabilization program on athletic performance in collegiate football players. JAthl 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 ofbalance 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.

24. Gribble P. The star excursion balance test as a measurement tool. Athl Ther Today. 2003;8:46-47.

25. Light KE, Purser JL, Rose DK. The functional reach test for balance: criterion-related validity of clinical observations. Issues Aging. 1995;18:5-9.

26. Earl JE, Hertel J. Lower-extremity muscle activation during the star excursion balance tests. J Sport Rehabil. 2001;10:93-104.

27. Gribble P, Hertel J. Considerations for the normalizing measures of the Star Excursion Balance Test. Measurements Phys Educ Exer Sci. 2003;7:89-101.

28. Olmstead LC, Carcia CR, Hertel J, Shultz SJ. Efficacy of the star excursion balance tests in detecting reach deficits in subjects with chronic ankle instability. J Athl Train. 2003;37:501-506.

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29. Hertel J, Miller SJ, Denegar CR. Intratester and intertester reliability during the starexcursion balance tests. J Sport Rehabil. 2000;9:104-116.

30. Raty HP, Impivaara O, Karppi SL. Dynamic Balance in former elite male athletes and incommunity control subjects. Scand J Med Sci Sports. 2002;12:111-117.

31. AkuthotaV, Nadler SF. Core strengthening. Arch Phys Med Rehabil. 2004;85S:S86-92.

32. Brandon R. Core stability training. Peak Perf. 2002;165:8-11.

33. Gambetta V. Following a functional path. Train Condit. 1995;5:25-30.

34. Arokoski JP, Valta T, Airaksinen O, Kanakaanpaa M. Back and abdominal muscle function during stabilization exercises. Arch Phys Med Rehabil. 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. Bergmark10,46 and Konin60 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 Norris44 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). Bergmark61, Konin60 and Norris44 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.

King54 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 Spine31

Global Muscles Local MusclesRectus abdominis MultifidiExternal Oblique Psoas MajorInternal Oblique Transversus abdominisIliocostalis Quadratus Lumborum

DiaphragmInternal Oblique (posterior fibers)Iliocostalis/Longissimus (lumbar portions)

Table B2. Norris Classification44

Postural PhasicQuadratus Lumborum Rectus abdominusErector Spinae Internal/External ObliqueIliospsoas GlutealsTensor Fascia Latae QuadricepsRectus Femoris Tibialis AnteriorPiriformis PeroneiPectineusAdductorsHamstringGastrocnemiusSoleusTibialis posterior

More information is needed to discuss the mechanisms by which muscles provide

stability to the spine.57 Studies59,62 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 studies9,34 evaluating various contributing factors to core

neuromuscular functioning. Arokoski34 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. Leetun9 looked at core stabilization strength

measures between males and females. Leetun9 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 studies31,58,46,47 in the literature have evaluated specific muscles of the core to

examine their properties and contributing roles. Recent research31,58,46,47 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 Johnson46 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 Johnson46 as well as other studies58,47 have indicated that the TVA precedes acceptance of

external loads and the onset of other muscles prior to movement. Hodges and Richardson9

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. Richardson45 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 Norris44 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. Leetun9 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 Chaffin72 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

study46 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.

Norris44 noted that imbalances of muscles leads to alteration of pelvic tilt and decrease range of

motion in spinal flexion.

Gracovetsky5 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, Panjabi6 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 Panjabi79 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

Bouisset9 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 Cholewicki9 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 Blackburn49 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 Irrgang40 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 Liemohn17 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 studies65,87 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 Strengthening31

Lumbar stabilization Dynamic stabilizationMotor control (neuromuscular) training Neutral spine controlMuscular 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 Lloyd50 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. Blackburn49 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 Richardson35 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 studies13,34,45,43,66,67,89,92,93 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 Norris43 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. Richardson45

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 Hess18 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 studies34,56,58,46,60,70,88,92 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 al34 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. Arokoski34 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. Johnson46 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 Skill46

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 Robinson90 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 Sall95 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 King48 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.

Jeffreys21 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 Jeffreys21 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 Balancein Tennis Athletes

IntroductionI, ____________________, have been asked to participate in this research study which has beenexplained to me by Kimberly M. Samson, BS, ATC. This research is being conducted byKimberly M. Samson, BS, ATC under the supervision of Michelle A. Sandrey, PhD, ATC tofulfill the requirements for a master’s thesis in Athletic Training in the School of PhysicalEducation at West Virginia University.

Purpose of the StudyI 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, rubbercoated and handheld, while Swiss Balls are air filled and rubber coated.

Description of ProceduresThis study will be conducted at the Athletic Training Clinic Laboratory and Old Gym atWaynesburg College, Waynesburg, PA 15370.

This informed consent form explains my rights as a research subject. I will be shown andvoluntarily 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 dynamicbalance using the Star Excursion Balance Test (SEBT). The test will be conducted one weekprior to and following the six-week exercise protocol. The SEBT involves a taped star patternwith 8 projections (excursions) each at 45 degrees from each other, on an even floor surface. Iwill place my non-dominant foot on the middle of the star pattern, while my dominant foot willbe reaching as far as possible in each of the 8 excursions. A practice session of 6 times in eachexcursion followed by a one minute rest and then the measured average in inches of three trialswill be included in the research data. Trials only count if I am able to maintain balancethroughout each excursion. Trials will be discarded and repeated if the reach foot is used toprovide considerable support when touching the ground, the stance foot is lifted from the centerof 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 onDynamic Balance in Tennis Athletes

The six- week protocol for the core stabilization-training program will be conducted as follows. Iwill follow the program 3 times a week for an average of 15-30 minute sessions. There will be 3progressive levels of exercises focusing on strengthening the abdominal, low back and pelvicmuscles while maintaining neuromuscular control. The exercises involve bending at the trunk ina sit-up like manner as well as bending backwards, at the sides, and rotating. I will start at levelone and progress through each level according to the protocol for that particular day.

Risk and DiscomfortsI understand that there are no known or expected risks from participating in this study. Mildmuscle soreness and the possibility of losing my balance are the only known or expecteddiscomforts with performing the Star Excursion Balance Test (SEBT) and core stabilizationexercises. While performing the SEBT, it is likely that I will not lose my balance because I willbe 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 thatKimberly M. Samson, BS, ATC will provide first aid and make any necessary medical referral.

AlternativeI understand that I do not have to participate in this study.

BenefitsI understand that this study may not be of direct benefit to me, but the knowledge gained may beof benefit to others.

Contact PersonsFor more information about this research, I can contact Kimberly M. Samson, BS, ATC at (724)852-3446 or at ksamson@waynesburg.edu or her faculty advisor, Michelle A.Sandrey, PhD, ATC at (304) 293-3295 Ext. 5220 or at msandrey@mix.wvu.edu. For informationregarding my rights as a research subject, I may contact the Professional DevelopmentCommittee Chair at Waynesburg College through Mr. AJ Anglin at (724) 852-3253.

68

The Effects of a Six-Week Core Stabilization-Training Program onDynamic Balance in Tennis Athletes

ConfidentialityI understand that any information about me as a result of my participation in this research will bekept confidential as legally possible. Identifying information on the informed consent form anddemographic/injury history questionnaire will be kept confidential by an assigned code numberto each informed consent form and demographic/injury historyquestionnaire. 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 orpresentations that result from this research, neither my name nor any information from which Imight be identified will be used without my consent.

Voluntary ParticipationParticipation in this study is voluntary. I understand that I am free to refuse or withdraw myconsent to participate at any point in this study and this will involve no penalty or loss of benefitsto which I am entitled to as a student athlete at Waynesburg College, that grades and classstanding will not be affected, and that status on the tennis team will not be affected. Treatmentand evaluation of injuries will also not be affected. I have been given the opportunity to askquestions about the research, and I have received answers concerning areas that I did notunderstand. In the event new information becomes available that may affect my willingness tocontinue to participate in this study, this information will be given to me so I may make aninformed 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 Balancein Tennis Athletes

IntroductionI, ____________________, have been asked to participate in this research study which has beenexplained to me by Kimberly M. Samson, BS, ATC. This research is being conducted byKimberly M. Samson, BS, ATC under the supervision of Michelle A. Sandrey, PhD, ATC tofulfill the requirements for a master’s thesis in Athletic Training in the School of PhysicalEducation at West Virginia University.

Purpose of the StudyI 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, rubbercoated and handheld, while Swiss Balls are air filled and rubber coated.

Description of ProceduresThis study will be conducted at the Athletic Training Clinic Laboratory and Old Gym atWaynesburg College, Waynesburg, PA 15370.

This informed consent form explains my rights as a research subject. I will be shown andvoluntarily 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 dynamicbalance using the Star Excursion Balance Test (SEBT). The test will be conducted one weekprior to and following the six-week exercise protocol. The SEBT involves a taped star patternwith 8 projections (excursions) each at 45 degrees from each other, on an even floor surface. Iwill place my non-dominant foot on the middle of the star pattern, while my dominant foot willbe reaching as far as possible in each of the 8 excursions. A practice session of 6 times in eachexcursion followed by a one minute rest and then the measured average in inches of three trialswill be included in the research data. Trials only count if I am able to maintain balancethroughout each excursion. Trials will be discarded and repeated if the reach foot is used toprovide considerable support when touching the ground, the stance foot is lifted from the centerof 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 onDynamic Balance in Tennis Athletes

If I am chosen for the control group I will not perform any of the core stabilization trainingexercises. I will be explained the guidelines of this group, and will be contacted on a weeklybasis and will be asked to answer all questions accurately and honestly.

Risk and DiscomfortsI understand that there are no known or expected risks from participating in this study. Mildmuscle soreness and the possibility of losing my balance are the only known or expecteddiscomforts with performing the Star Excursion Balance Test (SEBT) and core stabilizationexercises. While performing the SEBT, it is likely that I will not lose my balance because I willbe 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 thatKimberly M. Samson, BS, ATC will provide first aid and make any necessary medical referral.

AlternativeI understand that I do not have to participate in this study.

BenefitsI understand that this study may not be of direct benefit to me, but the knowledge gained may beof benefit to others.

Contact PersonsFor more information about this research, I can contact Kimberly M. Samson, BS, ATC at (724)852-3446 or at ksamson@waynesburg.edu or her faculty advisor, Michelle A. Sandrey, PhD,ATC at (304) 293-3295 Ext. 5220 or at msandrey@mix.wvu.edu. For information regarding myrights as a research subject, I may contact the Professional Development Committee Chair atWaynesburg College through Mr. AJ Anglin at (724) 852-3253.

71

The Effects of a Six-Week Core Stabilization-Training Program onDynamic Balance in Tennis Athletes

ConfidentialityI understand that any information about me as a result of my participation in this research will bekept confidential as legally possible. Identifying information on the informed consent form anddemographic/injury history questionnaire will be kept confidential by an assigned code numberto each informed consent form and demographic/injury historyquestionnaire. 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 orpresentations that result from this research, neither my name nor any information from which Imight be identified will be used without my consent.

Voluntary ParticipationParticipation in this study is voluntary. I understand that I am free to refuse or withdraw myconsent to participate at any point in this study and this will involve no penalty or loss of benefitsto which I am entitled to as a student or student athlete at Waynesburg College or West VirginiaUniversity, that grades and class standing will not be affected, and that academic status will notbe affected. Treatment and evaluation of injuries will also not be affected. I have been given theopportunity to ask questions about the research, and I have received answers concerning areasthat I did not understand. In the event new information becomes available that may affect mywillingness to continue to participate in this study, this information will be given to me so I maymake 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 StudentSeason with Waynesburg College tennis team: 1st/2nd/3rd/4th/5th/6th/Medical Red Shirt

Injury History

1. Have you had a lower extremity injury within the past six months that required theintervention of a medical or allied health care professional? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________2. Have you had an upper extremity injury within the past six months that required theintervention of a medical or allied health care professional? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________3. Have you had a head injury within the past six months that required the intervention of amedical or allied health care professional? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________4. Have you had any neurological disorders within the past six months that required theintervention of a medical or allied health care professional? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________5. Have you had any vestibular disorders within the past six months that required the interventionof a medical or allied health care professional? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________

73

6. Have you had any visual disorders within the past six months that required the intervention ofa medical or allied health care professional? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________

7. Are you currently taking any medications that might affect your ability to balance? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________

8. Have you completed or currently following a rehabilitation program for core stability withinthe past six months? Yes/NoIf yes, please explain:____________________________________________________________________________________________________________________________________________________________

9. Are you currently participating on the Waynesburg College men’s or women’s tennisteams? Yes/No

10. Are you currently involved in any other physical activity (i.e. weight lifting, aerobics,another sport) besides tennis? Yes/NoIf yes, please explain what other physical activities you are involved in and how often youparticipate in each activity:__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

74

Figure C1. Star Excursion Balance Test for a Right Limb Stance19

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 Stance19

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 tocontract their abdominals, drawing in their navel toward the floor without rotating thepelvis backwards. 3x20

Abdominal Muscle Contraction. Athlete will get in a quadruped position (on hands andknees) and will be instructed to contract their abdominals, drawing in their bellybuttontoward the ceiling without rotating their pelvis backwards. 2x15

77

Abdominal Muscle Contraction. Athlete will support themselves in a sideways posturewith their right forearm and right foot on the floor. Athlete will be instructed to maintaina straight alignment while contracting the right oblique muscle. The same will berepeated for the left side. 1x6/each side (10sec holds)

Level 1:Week 2

Day 4-6: Abdominal Muscle Contraction 1x20Dying Bug. Athlete will lie in a supine position with upper and lower extremitiesfacing straight toward the ceiling. Athlete will be instructed to maintain an abdominalcontraction while simultaneously moving their extremities toward the torso in slowcontrolled movements. 3x20

78

Bridging. Athlete will get in a quadruped position and be instructed to contract theirabdominals while simultaneously extending one leg back as straight as possible ina 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 upto 45 degrees. The athlete will have a medicine ball held with both hands and will beinstructed to rotate their upper torso with the arms extended while holding the medicineball 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 1x20Seated on Swiss Ball. Athlete will sit on a proper size Swiss Ball in an upright postureand will be instructed to contract their abdominals without rotating their pelvis backwardsand staying balanced on the Swiss Ball. 3x20

Squat with Swiss Ball. Athlete will be in a squat position with a Swiss Ball between themiddle of their back and a wall. Athlete will be instructed to maintain a proper squattingposture while contracting their abdominals during a squat. 3x15

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Superman. Athlete will lie on their stomach with the upper and lower extremitiespositioned straight out and fully extended. Athlete will be instructed to raise bothextremities at the same time not to exceed the onset of extreme low back arching. Bothextremities will return to their original starting positions in a controlled manner. 3x15

Level 2:Week 4

Day 4-6: Abdominal Muscle Contraction 1x20Multidirectional Lunge. Athlete will stand in upright posture with both hands on theirhip. Athlete will then do a lunge with their right knee and hip flexed to 90 degrees andtheir left knee flexed to 90 degrees, with their left hip at 180 degrees. The lunge will bedirected straight ahead and after going back to the original starting position, the lungewill be repeated with similar posture 45 degrees to the right. The same movement will beconducted for the left leg. 3x15

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Oblique Pulley with Side Shuffles. Athlete will partner up with another athlete. Oneathlete will be instructed to maintain the hold of a therapeutic resistance band and remainstationary, while the other athlete holds the other end with both hands in an extendedposition. The non-stationary athlete will do side shuffles to the point of minimalresistance and will then pull horizontally toward the non-stationary side, afterwards theathlete will side shuffle back to the original starting position. The athlete will do the sameactions 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 offeet away while holding a medicine ball with both hands at waist level. The athlete willturn their shoulders to the left and then toss the ball at the wall in a right diagonaldirection and immediately turn to the right and catch the ball while maintaining acontracted torso. The actions will take place in the opposite direction. 3x20

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Figure C5. Core Stabilization-Training Program Exercises: Level 3

Level 3:Week 5

Day 1-3: Abdominal Muscle Contraction 1x20Diagonal Curls on Swiss Ball. Athlete will have both feet planted on the floor whiletheir 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 turntoward an opposite knee, afterwards the upper body is returned to the original startingposition in a controlled manner. The same action will be repeated toward the oppositeknee. 3x10

Twists on Swiss Ball. Athlete will have both feet planted on the floor while theirupper back is supported on a Swiss Ball and their arms are extended toward the ceilingover their chest, holding a medicine ball. The athlete will then maintain stabilization oftheir lower body while moving their extended arms at the same time to one side of thebody, and then back to the original starting position, where they will do the same actionbut to the opposite side. 3x15

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Standing with Tennis Racquet on an Unstable Surface. Athlete will hold a tennisracquet in their dominant hand while standing on one leg. The athlete will then beinstructed to do forehand and backhand swings while maintaining balance. The sameactions will be conducted on the opposite leg. 4x10

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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 theexercise protocol for that day.

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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 asingle-leg stance while reaching with the opposite leg to touch as far as possiblealong a chosen excursion.

2. Subjects will be instructed to touch the farthest point possible as light as possiblealong a chosen excursion with the most distal part of their reach foot.

3. Subjects were instructed to return to a bilateral stance while maintaining theirbalance.

4. Subjects were instructed to perform six practice trials in each of the eightexcursions 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 restbetween each excursion.

7. Trials were discarded and repeated if the reach foot was used to provideconsiderable support when touching the ground, if the subjects’ stance foot waslifted from the center of the star grid, or if the subjects were not able to maintaintheir balance at any point in the trial.

8. The average scores for each excursion were recorded as the subjects’ dynamicbalance score.

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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

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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

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Table C8. Jeffreys Progressive Core Stability Program21

Classification Characteristic ExampleMastery of core contraction Static Isometric contraction Side bridge

Static holds and slow Static isometric contraction with controlled Dead bugmovements in stable simultaneous limb movementenvironment

Static holds in unstable Static isometric contraction on Abdominal isometricenvironment and dynamic a unbalanced surface/body movement contraction onmovement in a stable on a static surface Swissballenvironment

Dynamic movements in Body movement on an unbalanced Trunk twists onan unstable environment surface Swissball

Resisted dynamic Resisted body movement on an Trunk twists withmovement in unstable unbalanced surface Theraband onenvironment Swissball

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Table C9. Tests of Balance19

Static Tests Dynamic TestsStraight leg stance Functional reachRomberg Figure 8Tandem Romberg Gait (via video)Standing force plate measures Jumping from one surface to another

Vertical jumpBalance board

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APPENDIX D

ADDITIONAL RESULTS

Table D1. Descriptive Statistics for the Subjects (n=28)

Mean +

Age 20.18 1.02Height (cm) 171.31 9.57Mass (kg) 69.92 15.32

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Table D2. Descriptive Statistics for the Experimental Group and Control Group (n=28)

Core Stabilization-TrainingGroup

Control Group

Males 6 5Females 7 10

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Table D3. Descriptive Statistics for the Pre-Test Data for the Star Excursion Balance Test (n=28)

Group Mean + NPRE-TESTEXCURSIONAnterior Core 94.16 8.34 13

Control 88.71 7.00 15Anteromedial Core 95.88 8.64 13

Control 91.28 7.72 15Medial Core 97.99 7.57 13

Control 94.37 7.45 15Posteromedial Core 100.03 7.74 13

Control 98.7 8.35 15Posterior Core 100.62 7.46 13

Control 99.16 9.74 15Posterolateral Core 93.25 9.08 13

Control 91.66 8.85 15Lateral Core 85.31 11.15 13

Control 78.33 13.61 15Anterolateral Core 82.99 10.52 13

Control 78.90 6.00 15

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Table D4. Descriptive Statistics for the Post-Test Data for the Star Excursion Balance Test(n=28)

Group Mean + NPOST-TESTEXCURSIONAnterior Core 99.08 11.50 13

Control 90.62 7.38 15Anteromedial Core 102.18 10.47 13

Control 93.88 7.25 15Medial Core 106.70 10.15 13

Control 97.56 9.21 15Posteromedial Core 110.99 9.81 13

Control 103.17 9.77 15Posterior Core 110.77 8.59 13

Control 102.02 10.47 15Posterolateral Core 102.38 9.49 13

Control 94.26 9.94 15Lateral Core 91.42 10.06 13

Control 84.20 8.24 15Anterolateral Core 86.86 9.53 13

Control 82.19 6.91 15

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Table D5. One-Way ANOVA for the Pre-Test Data for the Star Excursion Balance Test (n=28)

df F P Value ESPRE-TESTEXCURSIONAnterior 1,26 3.527 .072 .275Anteromedial 1,26 2.216 .149 .332Medial 1,26 1.623 .214 .421Posteromedial 1,26 .189 .667 .614Posterior 1,26 .192 .665 .490Posterolateral 1,26 .219 .643 .506Lateral 1,26 2.162 .153 .340Anterolateral 1,26 1.652 .210 .421

* Significance at the .05 level (P<.05)

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Table D6. Main Effects and Interactions for Time, Group, and Time X Group for the StarExcursion Balance Test (n=28)

Excursion df F P Value ESTIME

Anterior 1,26 9.840 .004 .275Anteromedial 1,26 12.935 .001 .332Medial 1,26 18.904 .000 .421Posteromedial 1,26 41.440 .000 .614Posterior 1,26 25.020 .000 .490Posterolateral 1,26 26.599 .000 .506Lateral 1,26 13.395 .001 .340Anterolateral 1,26 18.872 .000 .421

GROUPAnterior 1,26 5.084 .033 .164Anteromedial 1,26 4.672 .040 .152Medial 1,26 4.591 .042 .150Posteromedial 1,26 2.064 .163 .074Posterior 1,26 2.477 .128 .087Posterolateral 1,26 2.094 .160 .075Lateral 1,26 3.461 .074 .117Anterolateral 1,26 2.077 .161 .074

TIME XGROUP

Anterior 1,26 1.920 .178 .069Anteromedial 1,26 2.234 .147 .079Medial 1,26 4.057 .054 .135Posteromedial 1,26 7.310 .012 .219Posterior 1,26 7.854 .009 .232Posterolateral 1,26 8.260 .008 .241Lateral 1,26 .005 .942 .000Anterolateral 1,26 .125 .726 .005

* Significance at the .00625 level (P<.00625)

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APPENDIX E

RECOMMENDATIONS FOR FUTURE RESEARCH

1. Since there is no set protocol for the duration of a core stabilization training program, usea variable workout schedule by evaluating training programs of 6 weeks, 9 weeks and 12weeks 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 programsrelated 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 bodyfatigue pre and post core stabilization-training program.

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