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LIBRARY
Michigan State
University

 

 

 

This is to certify that the

dissertation entitled

Acquisition of the Wheelchair Tennis Serve
By Wheelchair Users: Type of Model and
Frequency and Timining of Demonstrations

presented by

Kihong Kim

has been accepted towards fulfillment
of the requirements for

Ph .D. degree in Physical
Education and Exercise Science

 

 

fwd” ' @wWVA—U’L/

Major professor

Date December 15, 1994

 

MS U is an Affirmative Action/Equal Opportunity Institution 0-12771

 

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PLACE II RETURN BOX to remove this checkout“)!!! you! record.
TO AVOID FINES mum on at bdof. dd. duo.

 

 

 

 

 

 

 

 

 

ACQUISITION OF THE WHEELCHAIR TENNIS SERVE
BY WHEELCHAIR USERS: TYPE OF MODEL AND
FREQUENCY AND TIMING OF DEMONSTRATIONS

BY

Kihong Kim

A DISSERTATION

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

DOCTOR OF PHILOSOPHY

Department of Physical Education and Exercise Science

1994

ABSTRACT
ACQUISITION OF THE WHEELCHAIR TENNIS SERVE
BY WHEELCHAIR USERS: TYPE OF MODEL AND
FREQUENCY AND TIMING OF DEMONSTRATIONS
BY

KIHONG KIM

The primary purpose of this study was to determine the
effects of skill demonstrations by stand-up and wheelchair
models (type of model) on the acquisition of the wheelchair
tennis serve. The secondary purpose of this study was to
determine the effects of frequency and timing of
demonstrations on the acquisition of the wheelchair tennis
serve. Two studies were conducted. Study 1 was
conducted to determine the effects of model type on the
acquisition of the wheelchair tennis serve. The subjects
in Study 1 (E = 45) were randomly assigned to three
treatment conditions during 30-minute treatment period: (a)
wheelchair model condition; (b) stand~up model condition;
and (c) no model condition. In the results of Study 1,
demonstration by a similar model who used a wheelchair was
identified as the effective means for increasing form of the
wheelchair tennis serve. Wheelchair model and stand—up
model could influence motivational processes so that
positive incentive helped subjects maintain the ball
placement skill. The subjects who acquired high form

scores tended to show faster ball velocities compared to the

subjects who earned low form scores. Study 2 was
conducted to determine the effects of frequency and timing
of demonstrations on the acquisition of the wheelchair
tennis serve using the videotaped wheelchair model
demonstrations. The subjects in Study 2 (fl = 4) were
randomly assigned to four conditions designed by a multiple
baseline design during three 2—hour practice period. In
the results of Study 2, a higher frequency and an earlier
timing of demonstrations were the effective means for
increasing serve form in the wheelchair tennis. The
differences of physical conditions between subjects were
considered as the influence on the learning serve form in

the wheelchair tennis as well.

ii

DEDICATION

This dissertation is dedicated to
my father, Jungwhan Kim, who
always
helps me Open my eyes
toward the truth of life.
To my wife and daughter, Oekyung and Yerin Kim, too.

iii

ACKNOWLEDGMENTS

This dissertation was made possible through the efforts
and understanding of Dr. Gail M. Dummer who is my advisor.
I would like to express my sincerest gratitude to her.
Also, a deep debt of gratitude is extended to Mr. Jongoon
Kim for his great support and being there when I needed
help.

Further appreciation is extended to Dr. Deborah Feltz
for her expert guidance throughout method of this
dissertation. I would also appreciate Dr. John
Haubenstricker and Dr. David Stewart for their contributions
to this dissertation.

Special thanks is extended to Sangyeon Woo for
assisting me in the field of dissertation experiments and
sharing his much time during the final procedures of this
dissertation.

Finally, I take this Opportunity to express my love and
appreciation to my wife, Oekyung Kim, who always devotes
herself to support me and my daughter, Yerin Kim.

iv

TABLE OF CONTENTS

Pages
LIST OF TABLES O O O O O O I O O O O O O O O O O O O O I O O O O O O O O O I O O O O O O Viii
LIST OF FIGURES O O O O O O ........ O O O O O O O O O O O O O O O O O O O O O 0 ix
m;
I. INTRODUCTION ........ . ......................... 1
Statement of the Problem ...................... 4
Need for the Research . ........................ 4
Hypotheses
StUle ...0.0......OOOOOOOO......OOOOOOOOOO 8
Study 2 .. ........................... . ...... 9
Delimitations
Study 1 ............. ....... . .......... ..... 10
Study 2 ..... ........... .... ......... ....... 11
Limitations . ........ ............... ........ .....12
Definitions 0 O O O O O O O O O O O O O O O OOOOOOOOOOOOOOOOOO O 12
II. REVIEW OF RELATED LITERATURE ... ..... ... ....... 15

Methods of Teaching/Coaching
the Wheelchair Tennis Serve ......... ...... .... 16
Traditional Teaching/Coaching Methods ....... 16
Verbal Instruction ........................ 16
Visualization/Demonstration ............... 19
Kinesthesis ............................... 22
Importance of Model Characteristics ......... 24

Theoretical Perspectives ..... ...... ...... . 24
Effects of Model Characteristics .......... 28
Effects of Model Similarity ... ........ .... 36

Application of Modeling to Wheelchair Tennis. 39
Description of the Tennis Serve ............... 4O
Stand-up Tennis Serve Technique ............. 41
Grip ...................................... 42

Stance ..... ...... ......................... 42
Ball Toss ................... ......... ..... 43
Backswing .................... ............. 44
Forward Swing to Contact ... ..... . ..... .... 45
Follow-Through ............................ 45
Trunk Rotation .. .............. ....... ..... 46
Upper Limb Motion ......................... 46

III.

ElbOWACtion ...OO.......OOOOOOOOOOOOOOOOOO
Wheelchair Tennis Serve Technique ...........

Methods of Assessing the Tennis Serve Technique.

Assessment of Biomechanical Variables ........
Ball Velocity .............................
Racket Velocity . ................. .........
Angle of Projection .......................
Center of Gravity .........................
Ground Reaction Forces ....................

Field Tests for Tennis Serve Performance ....
Ball Velocity .......... . ..................
Placement .................................

Conclusion ....................................

STUDY 1 .......................................

Methods ....... . ...............................
Research Design ........ .....................
Independent Variables ............. ... .....
Dependent Variables ..... ..................
Experimental Design .......................
Rationale for Experimental Design .........
Subjects ....................................
Subject Selection Procedure ...............
Subject Characteristics ...................
Assignment of Subjects to Treatment Groups.
Instrumentation .............................
Data-Collection Procedures........... ....... .
Pretest and Posttest in the Wheelchair
Tennis Serve .............. . ...............
Equipment for Serve Test ..................
Test for Serve Form .......................
Test for Ball Velocity .... ............... .
Test for Serve Placement ..................
Intervention ................................
Typical Intervention Session ..............
Verbal Instruction ........................
Types of Models ..... ......................
Wheelchair model ........................
Stand-up model ..........................
No model ..... . ..........................
Statistical Analyses ........................
Results and Discussion for Study 1 ............
Results .....................................
Hypothesis 1 ..............................
Hypothesis 2 ..............................
Hypothesis 3 ..............................
Intercorrelations Among Three
Dependent Variables .. .....................
Discussion .... ..............................

vi

50

IV. STUDY 2

Methods ....................................... 102
Research Design ............................. 102
Independent Variables ..................... 102
Dependent Variables ....................... 103
Experimental Design ....................... 103
Subject #1 .............................. 103
Subject #2 .............................. 103
Subject #3 .............................. 105
Subject #4 ................ ... ........... 105
Rationale for Experimental Design ......... 106
Subjects .................................... 107
Subject Selection Criteria .... ............ 107
Identification of Potential Subjects ...... 107
Subject Selection Procedure ............... 108
Subject Characteristics ................... 109
Subject #1 .............................. 110
Subject #2 .......... . ................... 110
Subject #3 .............................. 110
Subject #4 .............................. 111
Assignment of Subjects to Groups .......... 111
Instrumentation ............................. 111
Data-Collection Procedures .................. 112
Warm-Up Session ... .............. ..... ..... 112
Test Blocks ....... .... ......... .... ....... 112
Intervention .............................. 113
Instruction Procedures ................... 113
Statistical Analyses ........................ 113
Results and Discussion for Study 2 ............ 115
Results ..................................... 115
Hypothesis 1 .............................. 117
Hypothesis 2 .............................. 123
Hypothesis 3 .............................. 128
Discussion .................................. 133
V. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS ..... 140
Summary ..................................... 140
Study 1 ................................... 141
Study 2 ................................... 142
Conclusions ................................. 144
Recommendations ............................. 145
LIST OF REFERENCES ................................. 147
APPENDICES
A. HUMAN SUBJECT APPROVAL AND
INFORMED CONSENT FORM ...................... 154
B. LETTERS OF SUPPORT ......................... 157
C. DATA COLLECTION FORMS ...................... 159
D. RAW DATA ................................... 163

vii

LIST OF TABLES

Table Pages

 

1. Number, Gender, and Age of Subjects Attending
The Interventions ......OOOOOOOOOOO......OOOOOOOOOO 66

2. Description of Model's Performance in Tennis Serve
Tested by Three Dependent Measures................. 74

3. Intervention by the Types of Models ..... .......... 77

4. Serve Form Scores (Percentage of Successful Steps)
by Treatment Condition ............................ 83

5. Average Ball Velocity (mph)
by Treatment Condition ....... .................. ... 87

6. Ball Placement Scores (Percentage of Successful
Serve) by Treatment Condition ..................... 90

7. Intercorrelations
among Three Dependent Variables ......... ..... ..... 94

8. Serve Form Scores
(Percentage of Successful Steps) .................. 118

9. Average Ball Velocities (mph) ..................... 124

10. Ball Placement Scores
(Percentage of Successful Serve) ................... 129

viii

LIST OF FIGURES

Figure Pages
1. A diagram of experimental design for Study 1 ....... 60
2. Tennis court diagram and dimensions ................ 68
3. Data collection setting on the serve court ......... 71
4. A diagram for statistical analyses in Study 1 ...... 81

5. Treatment condition by trials interaction for serve
form scores (percentage of successful serve) ........ 84

6. Treatment condition by trials interaction for ball
velOCity ............OOOOOOOOOOOOOOO......OIOOOOOOOO 88

7. Treatment condition by trials interaction for ball
placement scores (percentage of successful serve)... 91

8. A diagram of experimental design for Study 2 ...... .104
9. A diagram of statistical analyses for Study 2 ......116

10. Percentage of serve form scores over 30 blocks of
serve teSt I. ..... ......OOOOOOOOOOOO0.0.0.0000000000119

11. Data patterns (level and slope) for serve form
scores over 30 test blocks ......................... 120

12. Standard deviations for serve form scores
over 30 test blocks ....... ................ . ........ 121

13. Average ball velocities (mph) over 30 blocks of
serve test .........................................125

14. Data patterns (level and slope) for ball velocities
over 30 test blocks ............. ..... ..... ...... ...126

15. Standard deviations for ball velocities
over 30 test blocks ........ ........... . ............ 127

16. Percentage of ball placement scores over
30 blocks of serve test.............................130

17. Data patterns (level and slepe) for ball placement
scores over 30 test blocks ......................... 131

ix

CHAPTER I

INTRODUCTION

Sport competition for individuals with disabilities,
including wheelchair users, has seen enormous growth since
World War II (DePauw, 1984). The number of wheelchair
athletes has increased due to many organized wheelchair
Sport competitions in a wide variety of sport activities.
Now there are yearly competitions held at local, national,
and international levels (Hunt & Lykins, 1990).

The responsibility of professionals who take the role
of teaching sport skills to the individual with disabilities
must be to provide successful instruction which is
apprOpriate for the special needs of the learners with
disabilities. For this reason, those professionals need
effective means of teaching and coaching to ensure personal
success in learning sport skills and access to a healthy
lifestyle.

The technique of demonstration is one of the most
effective tools in teaching sport skills to the individual
with disabilities (Fait & Dunn, 1984). Differences
between the various disabilities should influence how an

activity is taught. Specifically, wheelchair users are

2
likely to receive a dissimilar demonstration in learning
sport skills because the teacher's demonstration usually is
performed in the standing position despite the learner's
sitting position. This dissimilar demonstration is
questionable as an effective teaching method for the
wheelchair user’s acquisition of the target skills in sport
activities.

According to research in sport psychology,
characteristics of the teaching model are emphasized as
important factors in producing effective instruction.
Modeling seems to be an accepted form of instruction for
teaching motor skills in physical education (Magill, 1989).
The status of the model is a factor that has been identified
as influential in the phenomenon of imitative behavior
(Landers & Landers, 1973). Wiese-Bjornstal and Weiss
(1992) noted that the process of modeling serves its most
important function in the demonstration and acquisition of
Sport skills within the realm of sport and physical
education. According to Bandura's (1969) social learning
theory, model characteristics are presumed to influence
attentional and retentional subprocesses as a means of
observational learning. Much research examining the
relationship between modeling and motor performance has been
based on Bandura's theory (1969), in which modeling is

conceptualized as an informational process whereby observers

3
are cognitively engaged as central information processors
(Bandura, 1986).

Model characteristics such as competency (Baron, 1970),
prestige (Mausner, 1953), status level (Landers & Landers,
1973), age (Bandura & Kupers, 1964), and similarity (George,
Feltz, & Chase, 1992; Gould & Weiss, 1981; McCullagh, 1987)
have been investigated as variables which may influence the
degree of observational learning. Model similarity, one
of those variables, is the main issue in this study. A
similar model is more effective for successful performance
than a dissimilar model, that may enhance the observer's
performance as well. The effects of model similarity can
be applied to wheelchair tennis, and skill demonstrations in
wheelchair tennis can be developed based on modeling theory.

While investigators have reported various conclusions
concerning the influence of model characteristics on motor
skill acquisition, no conclusion has been structured for the
acquisition of motor skills by wheelchair athletes through
modeling techniques. Since there is an obvious lack of
scientific evidence regarding the effects of modeling in
wheelchair tennis, this study attempted to investigate
effects of model type, as well as the frequency and timing
of demonstrations on the acquisition of the wheelchair
tennis serve by wheelchair users. There were two studies
for the purpose of this study. The first study was

designed to investigate performance differences dependent on

4
type of model. The wheelchair model as a similar model in
wheelchair tennis and the stand-up (nondisabled) model as a
dissimilar model were the main treatments in teaching the
wheelchair tennis serve to beginning players in Study 1.
The tennis serve performance was tested by serve form, ball
velocity, and ball placement. The second study was
designed to investigate performance differences dependent on
the frequency and timing of demonstrations. Frequency and
timing of demonstrations were the main treatments in the
multiple baseline design of Study 2. The effects of these
treatments on the acquisition of the wheelchair tennis serve
skills were tested by serve form, ball velocity, and ball
placement.
Statement of the Problem

The purpose of Study 1 was to determine the effects of
two types of skill demonstrations (stand-up model and
wheelchair model) on the acquisition of the wheelchair
tennis serve by wheelchair users. The purpose of Study 2
was to determine the effects of the frequency and timing of
demonstrations on the acquisition of the wheelchair tennis
serve by wheelchair users.

Need for the Research

There is an urgent need for empirical evidence to
verify the many claims and hypotheses concerning teaching
sports skills in wheelchair sports. Despite the increased

pOpularity of wheelchair sports nationally and

5
internationally, there are few research studies involving
wheelchair sports and recreation. Many important
questions about effective methods of teaching and coaching
sport skills have not been addressed either theoretically or
through empirical studies (Higgs, 1990). While many
physiological studies have been focused on wheelchair
athletes, little attention has been given to the acquisition
of sport skills by wheelchair users based upon psychological
perspectives.

Tennis is one of the most pOpular and fastest growing
wheelchair sports today. Its minimal adaptations, readily
available facilities, and low-cost equipment have made
tennis one of the most popular sports for individuals with
physical disabilities in the United States. Wheelchair
tennis provides not only an excellent option for competitive
integration of individuals with disabilities and those
without disabilities in Sport, but it also contains the
necessary characteristics for an effective activity of body
awareness (Tripp & Rogers, 1990).

The National Foundation of Wheelchair Tennis (NFWT) is
the governing body for wheelchair tennis in the United
States. Since its inception in 1976, NFWT evolved out of
efforts to promote awareness of the abilities of wheelchair
athletes and has done for wheelchair tennis players what
Wimbledon and the U.S. Open have done for able-bodied tennis

players (Paciorek & Jones, 1994). Known as the “Wimbledon

6
of wheelchair tennis," the United State Open Wheelchair
Tennis Championship is one of the most famous wheelchair
sport competitions and is attended by more than 300
wheelchair tennis players from around the world every year.
Also, NFWT provides for the development, promotion, and
exposure of wheelchair tennis through clinics and
exhibitions.

The benefits of participation in sport activities for
those with impairments or disabilities are extensive,
including enhanced levels of fitness, skill development, and
an improved sense of self-worth. The reasons that
wheelchair users enjoy participating in sport and recreation
are essentially the same as those commonly espoused by the
nondisabled (Hunt & Lykins, 1990). Henschen, Horvat, and
French (1984) noted that the development of self-control
and self-discipline, increase in social status, worthy use
of leisure time, increase in physical well being,
Opportunity for competition, and opportunity to develOp
teamwork and c00peration were considerable values of
wheelchair sports. Specifically, with improvement in
self—confidence for tennis tasks, adolescents who use
wheelchairs perceived that they had increased ability for
other physical tasks (Hedrick, 1985). In recent experiment
by Greenwood, Dzewaltowski, and French (1990), they
concluded that wheelchair tennis participants were more

confident about general wheelchair mobility tasks than were

7
nonparticipants. Those benefits should be available for
wheelchair users who are persistent in a sport activity.
When they are reasonably successful in a sport activity,
they may tend to persist longer. Therefore, better
teaching methods should be developed to increase success in
wheelchair sports.

The technique of demonstration to enhance performance
has been used in many investigations related to motor skill
acquisition settings but not studied in wheelchair tennis.
This practical approach to enhance teaching methods in
wheelchair tennis can be used as one modeling technique for
adapted physical educators, physical education teachers,
tennis coaches, or parents who teach wheelchair tennis.
Many wheelchair users play tennis, so effective teaching
methods would benefit those wheelchair users who participate
in wheelchair tennis. Also, effective teaching methods
developed for the wheelchair tennis serve may generalize to
other sport skills.

Seeing role models was considered to be an important
means for learning values, attitudes, and other social
behaviors (Bandura, 1977). There has been a recent
increase in interest in knowing more about the use of
modeling for teaching motor skills. When teaching someone
a novel skill or when attempting to modify one's existing
skill level through demonstrations, elements contained

within the demonstration may have an influence on a

8
performer’s subsequent responses. Three elements of the
demonstration were identified that have been shown to
influence performance levels: (a) augmented information may
be provided in addition to the visual information inherent
in the demonstration; (b) the cognitive elements of the task
may influence the extent of modeling effects; and (c) the
characteristics of the demonstrator or model may influence
performance (McCullagh, Weiss, & Ross, 1989). Bandura
(1986) emphasized the need for role models in observational
learning noting that higher status persons are imitated more
frequently than lower status persons.

Generally, the more similarity between demonstration
model and the observer, the more likely that the observed
performance outcome will have meaning for the observer
(Magill, 1989). Randy Snow, eight-time world—championship
wheelchair tennis player, is conducting Snow tennis camps,
where wheelchair tennis players of all ages and ranks from
several states come to learn from Snow's expertise. Is
there any more positive effect when Randy, as a similar
model (wheelchair model), is teaching tennis for the
wheelchair individuals? This question can be studied in
the view of modeling theory in skill instruction.

Hypotheses
Study 1
The following research hypotheses were examined in

Study 1:

9

1. Able—bodied students receiving a videotaped
demonstration by a model who uses a wheelchair will show the
greatest improvement in the wheelchair tennis serve skill
tested by a form checklist compared to able-bodied students
viewing a stand-up model or no model.

2. Able-bodied students receiving a videotaped
demonstration by a model who uses a wheelchair will show the
greatest improvement in the wheelchair tennis serve skill
tested by ball velocity compared to able-bodied students
viewing a stand-up model or no model.

3. Able-bodied students receiving a videotaped
demonstration by a model who uses a wheelchair will show the
greatest improvement in the wheelchair tennis serve skill
tested by ball placement compared to able-bodied students
viewing a stand-up model or no model.

Study 2

The following research hypotheses were examined in
Study 2:

1. A wheelchair user receiving a higher frequency of
demonstrations and an earlier introduction of demonstrations
of the wheelchair tennis serve during a series of learning
trials will show greater improvement in the wheelchair
tennis serve skill tested by a form checklist compared to
wheelchair users receiving a lower frequency and later

introduction of demonstrations.

10

2. A wheelchair user receiving a higher frequency of
demonstrations and an earlier introduction of demonstrations
of the wheelchair tennis serve during a series of learning
trials will show greater improvement in the wheelchair
tennis serve skill tested by ball velocity compared to
wheelchair users receiving a lower frequency and later
introduction of demonstrations.

3. A wheelchair user receiving a higher frequency of
demonstrations and an earlier introduction of demonstrations
of the wheelchair tennis serve during a series of learning
trials will show greater improvement in the wheelchair
tennis serve skill tested by ball placement compared to
wheelchair users receiving a lower frequency and later
introduction of demonstrations.

Delimitations
Study 1

The scope of Study 1 was delimited by the following
factors:

1. The demonstration model for both the wheelchair
serve and stand-up serve was the investigator himself.

2. The subjects in Study 1 were able-bodied students
who had not previously played tennis.

3. All subjects were able-bodied undergraduate or
graduate students attending Michigan State University.

4. All subjects used the same wheelchair while

performing the wheelchair tennis serve.

11

5. The number of subjects was 45, who were randomly
assigned to one of three different treatment groups.

6. The instructional period was 30 minutes.

7. An attempt was made to eliminate practice outside
the instructional period.

8. All subjects were tested using the same tennis
racket with same string tension.

9. The wheelchair tennis serve skill was assessed by
serve form, ball velocity, and ball placement.

Study 2

The scope of Study 2 was delimited by the following
factors:

1. The demonstration model for the wheelchair tennis
serve was the investigator himself who used a wheelchair to
perform the wheelchair tennis serve.

2. The subjects were wheelchair users who had no prior
experiences in tennis play.

3. All subjects were undergraduate students with
disabilities attending Michigan State University.

4. The number of subjects were four out of six
potential subjects, who were randomly assigned to one of
four conditions of multiple baseline design.

5. The instructional period was one week.

6. An attempt was made to eliminate additional practice

beyond the actual instructional period.

12

7. The wheelchair tennis serve skill was assessed by
serve form, ball velocity, and ball placement.

8. Physical disabilities of four subjects were
classified by two men with incomplete quadriplegia, one
woman with paraplegia, and one woman with an amputation of
the right leg.

Limitations

This study was limited by the following uncontrolled
factors:

1. The sampling method was not controlled by perfect
random sampling in Study 1 and Study 2.

2. An assumption was made that the subjects would be
performing to the best of their ability during the
wheelchair tennis serve test in Study 1 and Study 2.

3. No effort was made by the investigator to control
such factors as sleep and nutrition that may influence the
performance of each subject in Study 1 and Study 2.

4. Study 1 and Study 2 were concerned only with the
wheelchair tennis serve skill.

5. The model characteristics were concerned only with
the types of model demonstrations in Study 1.

6. One type of model (wheelchair model) was used in
Study 2.

Definitions
The following terms will be used throughout this study

and intervention:

13
gall velocity - Vector quantity expressing the average
change in linear displacement of a served tennis ball per

unit of time (Hay, 1978).

Modeling - A general process whereby an observer reproduces
the overt actions exhibited by a model. Such

demonstrations are considered to be an effective means of
teaching a variety of behaviors, attitudes, values, and
skills (Bandura, 1969).

Model type - The demonstration model used in this study was
the investigator, himself. Shown on a videotape, the two
types of model were (a) a wheelchair model who used a
wheelchair to demonstrate the wheelchair tennis serve, and
(b) a stand-up model who performed tennis serve in standing
position to demonstrate tennis serve skill for wheelchair
users.

Placement of serve — The location where a served tennis ball
lands in the Opponent's service court.

Stand-up model (nondisabled model) - A person without
disability who provides a demonstration of a skill from a
standing position.

Serve testyblock - One test session consisting of 10 tennis
serves.

Serve trial - An execution of one tennis serve.

Tennis serve skill - The ability to serve into the
opponent’s serve court with traits of Speed, depth, and

consistency.

14
Wheelchair model - A person with or without disabilities who
provides a demonstration of a Skill from a seated position
in a wheelchair.
Wheelchair Tennis - A game played according to the rules of
regulation tennis except for modifications necessitated by
wheelchair tennis players. The most obvious modification
is the "two bounce rule," where the ball must be returned

after bouncing not more than two times (Paciorek & Jones,

1994).

CHAPTER 11

REVIEW OF RELATED LITERATURE

The purposes of this study were to (a) examine the
effects of demonstrations by model types (stand-up model and
wheelchair model) and (b) determine the effects of different
frequencies and timing of demonstrations on the acquisition
of skill in the wheelchair tennis serve. Teaching or
coaching methods were identified via modeling theory.
Therefore, in the first section of this chapter, traditional
teaching or coaching methods are presented, including the
importance of model characteristics and the applications of
modeling to wheelchair tennis. In the second section of
this chapter, selected literature on the tennis serve,
including tennis serve techniques for non-disabled player as
well as wheelchair users, is reviewed. In reviewing
tennis serve techniques, the instructional cues for the
tennis serve are presented in a style easily comprehended by
beginners. Methods of assessing the tennis serve are
reviewed in the third section of this chapter. These
studies helped the investigator determine the most effective

method of assessment for the wheelchair tennis serve.

15

16
Methods of Teaching/Coaching
the Wheelchair Tennis Serve
W

The main purpose of this section is to identify the
methods of teaching or coaching sports skills that are most
effective for teaching the wheelchair tennis serve skill
based on modeling theory. Teaching sport skills
effectively requires advanced instructional planning and an
understanding of the skill learning process in relation to
the instructional process.

Christina and Corcos (1988) emphasized the coach's
responsibilities including choice of instructional method.
In instructional methods, introduction, explanation, and
demonstration were included. These methods are common to
physical education teachers in teaching Sport skills.
Physical education teachers employ Special teaching
techniques for managing instructional problems efficiently
and for responding effectively to the different students.
In teaching sports skills or motor skills, techniques of
teaching used by physical education teachers are of three
general types: verbalization, visualization, and kinesthesis
(Fait & Dunn, 1984).

Verbal Instruction

The spoken word used in the process of teaching is

referred to as verbalization. Describing a skill or

explaining the strategy of a tennis play are examples of the

17
use of the technique. The oral presentation of a motor
problem is included under verbalization. This technique
has advantages for certain pOpulations such as individuals
with visual impairment. Verbalization technique
frequently is employed to clarify a concept of a
demonstration (Fait & Dunn, 1984).

Christina and Corcos (1988) insisted that verbal
pretraining should be a part of the explanation of skills.
Although not effective for all athletes or for learning all
skills, this technique is very useful when athletes have to
learn a sequence of actions or procedures that are initially
difficult to remember. Verbal pretraining are provided by
simple word labels to help remind the athletes of what to do
next while executing a complex skill.

Luria (1958, 1961), a Soviet psychologist, introduced
the role of language as a critical factor in the control of
overt behavior. According to Luria's theory (1961)
children's behavior progress through four developmental
stages. In the first stage, from one and one-half to
three years, infants' actions are influenced not by their
own Speech but by adult verbal guidance because of their
inability to direct their actions through their own Speech.
In the second stage, between three to four and one-half
years, children start to demonstrate the ability to use
self-verbalization to initiate motor behavior. The third

stage, from four and one-half years on, is when children

18
Show the ability to initiate and inhibit actions. In the
final stage, the fourth stage, overt self-regulating speech
become inner or covert speech, which predominates over motor
behavior.

Flavell, Beach, and Chinsky (1966) were stimulated by
Luria's theory and used stage theory to determine the role
of Speech regulation in children's performance of selected
cognitive and motor tasks. Subjects (H = 60) were 10 boys
and 10 girls randomly drawn from the kindergarten, second
and fifth grades. Flavell et a1. (1966) indicated that
younger children did not spontaneously label objects nor use
verbal rehearsal strategies unless cued to do so. They
concluded that verbal production deficiency existed in young
children.

Keeney, Cannizzo, and Flavell (1967) examined
spontaneous and induced verbal rehearsal of first grade
children in a serial recall task and agreed with the
conclusion of Flavell et a1. (1966). In their study, the
children's unmediated behavior was explained as a production
deficiency rather than a mediational deficiency.

Meichenbaum and Goodman (1971) studied the use of
verbal rehearsal with two groups of children who were
impulsive and nonimpulsive. The kindergarten children
were taught to disregard a yellow light and to push a foot
pedal only when a blue light appeared. The verbal cues,

such as push or don't push, were said when a light came on.

19
Use of the self-talk strategy aided performance of the task
in both the impulsive and nonimpulsive groups.

Christina and Corcos (1988) noted the existing
limitations of verbalization. Understanding the concept
of a Skill with a verbal explanation alone is often
difficult, especially when the skill is complicated or the
learners are young or inexperienced. McCullagh, Weiss,
and Ross (1989) insisted that verbal rehearsal strategies,
when combined with demonstration, facilitated acquisition of
a motor skill.

VisualizationzDemonstration

Visualization refers to a technique that employs visual
attention by the students. Many techniques are included
under this general heading such as demonstrations, motion
pictures, videotape, film-strips, posters and pictures,
diagrams, and the printed word.

One of the most effective tools is a demonstration
where students attempt to execute the skill by duplicating
the demonstrated movements that they have observed (Fait &
Dunn, 1984). The teaching of most sport skills is greatly
enhanced if either the teacher or a student leader can
effectively demonstrate the skill being taught. Christina
and Corcos (1988) explained the demonstration of sport
skills. Although a clear, brief explanation lets the
athletes know exactly what the coach want them to do, the

best way to understand the skill is to supplement the

20
introduction and explanation with demonstrations designed to~
illustrate the specific points of the skill. Appropriate
demonstration in teaching motor Skills is referred to as
modeling. Modeling increases the student's repertoire of
desirable behaviors or apprOpriate motor skills.

Modeling, learning through observing and imitating others,
has been extensively utilized in physical education and also
successfully employed with individuals with disabilities
(Sherrill, 1981).

Modeling has been one of the most important
instructional strategies for broadening the physical skills
and sport skills of children and adolescents because visual
information is such a powerful means of conveying
information about sport skills (Weiss, Ebbeck, & Rose,
1992). The demonstration was the best means of modeling a
skill for students to get an idea of what they should be
doing (SiedentOp, 1983).

Anderson, Gebhart, Pease, and Ludwig (1982) examined
the effect of subjects' age and the temporal placement of a
modeled skill on the performance of a balance test.

Subjects aged 7 and 9 years old (3:60) were randomly
assigned to two temporal spacing conditions (before the task
or the middle of the task) and no model control group.
Time-on-balance and time-off-balance data on a stabilometer
were collected for subjects exposed to the different

modeling conditions. Tape-recorded instructions were

21
given to all groups before the task. Two modeling groups
viewed a videotape of their physical education instructor
showing how to balance on the stabilometer. Results
indicated that 7 year-old boys who received a demonstration
improved more in the balance task than students in the no
model group, but not for 9 year-old boys. No significant
differences were found based on temporal spacing (before or
the middle of the task). The results were not strong
enough to support the effect of modeling because all
subjects who were 7 year-old or 9 year-old boys did not
perform differently under the three conditions (before,
middle, no model) for time on balance.

Carroll and Bandura (1985) examined the role of the
timing of visual monitoring and motor rehearsal in
observational learning strategies. Subjects (fle60), 30
male and 30 female undergraduate students, were randomly
assigned to one of three treatment groups in which they
observed a videotape of a model performing a complex action
pattern. After observing 12 repetitions of a modeled
action, all subjects performed the task in one of three
treatments with either concurrent, delayed, or no visual
monitoring. Subjects receiving concurrent feedback could
see their actions on a television monitor as they performed.
Subjects receiving delayed feedback viewed their actions
after a 25 second delay. The treatment groups were each

divided into two levels (motor rehearsal vs. no motor

22

rehearsal). The modeled action was broken into
components, and the subject's movement was measured by its
similarity to the modeled components in form and sequence.
:[11 scoring the movement of the subject, point deductions and
Jucrwer reproduction scores resulted from the subject's errors
jrrx form and sequence. The investigator concluded that
nmanle and female undergraduate students performed better and
.ijznproved reproduction accuracy in observational learning by
<:<:rncurrent visual monitoring.
W

As beginning tennis players adjust their grip during
learning tennis skills, the involvement of muscular activity
:le. learning is referred to as the use of kinesthesis (Fait &
Dunn, 1984). The kinesthetic receptors in the joints are
1>€3ilieved most vital to the perception of space and movement.
rPile amount of information which is obtained from muscles and
‘tfialadons is limited. Specifically, muscle receptors
rtegister stretch and rate of stretch, and tendon receptors
riisgister strain. Kinesthetic perception and memory are
‘tllee basis of voluntary movement and motor learning. This
Parception and memory enables the students to initiate a
‘V11<Jle movement pattern or modify a part of it, such as the
Eflimination or addition of a joint action, or a change in

the timing or speed of an action (Luttgens & Wells, 1982).

23

Gallwey (1974) made some useful suggestions for
heightening kinesthetic awareness in tennis players that can
easily be generalized tO all Sports. He suggested that
tennis players might benefit from undergoing some
sensitivity training, which can be accomplished by focusing
their attention on their bodies during practice. Ideally,
a teammate or ball machine would throw balls tO the tennis
player that bounce in approximately the same Spot each time.
Then, paying relatively little attention tO the position of
ba 11, the players can experience what it feels like to hit
the ball. The player should concentrate on feeling the
exact path Of the racquet on the backswing. However,
attention Should be mainly focused on the feel Of the arm
and hand at the moment just before they swing forward tO
Itleet the ball.

Many coaches are aware Of the problems with this
kinesthetic approach. Beginners are unable tO identify
the feel Of a movement because they have nothing with which
to compare it. On the Opposite end Of the performance
Continuum, highly skilled players might suffer from what has
been termed "paralysis from analysis." Knowing when to
enlphasize the feel Of a skill, and with which athletes tO
try this approach, is a prime example Of why coaching is an
Eiltt as well as a science (Christina & Corcos, 1988).

In summary, research suggests that a most efficient

teaching method is visualization with verbal introduction.

24
The visualization could be represented by a model's
demonstration which has a positive influence on motor
performance. In addition, the kinesthetic method is
helpful for students who cannot identify the feeling Of
movement or form in tennis play.
Importance of Model Characteristics

_'1;1_1yeoretical Perspectives

According tO Bandura's (1969) theory, informational and
motivational processes both are important in imitative
behavior. Four subprocesses in informational and
motivational processes are attentional, retentional, motor
reproduction, and motivation subprocesses. These
subprocesses are presumed to govern Observational learning.

The attentional subprocess regulates the perception Of
1n<><zle1ed activities. In the retentional subprocess,
experiences are converted into symbolic representations for
111elttory. The motor reproduction subprocess controls the
Organization Of subskills into new response patterns, and
the motivational subprocess determines if Observationally
a<=<1uired skills will be used (Bandura, 1986). Attentional
and retentional subprocesses are hypothesized to control
acquisition while motor reproduction and motivation
SIllaprocesses are hypothesized tO control performance
(McCullagh, 1986).

According tO Bandura (1969), selective attention is one

Of the crucial subfunctions in Observational learning.

25
Attention is the ability tO notice significant features of a’
modeled behavior, so that the features are accurately coded
into memory. Christina and Corcos (1988) emphasized that
coaches must first get their athletes' attention by
effectively introducing the skill and directing the
learner's attention to the key points Of each phase of the
movement. They also insisted that unless the Observer is
paying attention to the key points, the demonstration will
be ineffective. If the Observer fails tO attend to,
recognize, and differentiate the Significant features in a
demonstration, then he/she is not able to acquire matching
behavior at the sensory integration level. In Bandura's
discussion Of the factors that influence an individual's
attention in Observational learning, model characteristics
are included among those factors. Model characteristics
such as age, competence, prestige, status level, social
power, and Similarity are presumed tO influence the
attentional subprocess (McCullagh, 1986).

Another factor which influences the attentional
subprocess is the social and symbolic environment. The
maintenance Of attention in ongoing activity is directly
affected by the consequences Of the behavior being Observed.
Anticipated benefits Of modeled performance provide
incentive for paying attention (Bandura, 1986).

The retentional subprocess in Observational learning

involves the active process Of transforming and

26
restructuring information about modeled actions into
symbolic form. Bandura (1986) explained that what the
learner Observed might be transformed into concise symbols
which represented the essential features and structures Of
the activity. In Bandura's description Of retention, two
representational systems are encompassed. Imaginary and
verbal representational systems are those two components.
The imaginary system for visual memory plays a primary role
in Observational learning during early develOpment and
continues to function as a significant retention aid after
linguistic skills are acquired. Verbal symbols in the
verbal representational system permit the coding Of modeled
events in verbal-conceptual form. In the Coaches Guide tO
Teaching Sport Skills, Christina and Corcos (1988) mentioned
that repetitions of the same cues with each successive
demonstration would be the most effective for Optimal
retention Of an athletic Skill. Attention and retention
Of the demonstration are essential for learning sport
skills. It is through these first two steps that learners
acquire a basic understanding Of the target skill.

In order tO understand the reproductive subprocess,
Bandura (1986) suggested that conceptual-motor mechanisms Of
performance must be analyzed. This motoric reproductive
subprocess involves converting symbolic representation Of a
modeled behavior tO motor output. Cognitive selection and

organization Of response elements, centrally guided

27
initiation, monitoring response enactments, and matching
action to conception are processed within conceptual-motor
mechanisms.

Conception Of the action to be modeled is derived at
the cognitive level through the selection and organization
Of action models. Accurate conceptual representation
helps learners acquire the adequate performance Of modeled
action. Initiation and production Of the modeled action is
guided by the conceptual representation. The rate and
level Of Observational learning as well as the smoothness Of
reproduction are affected by motor proficiency.

Mismatched or poorly learned motor skills cause errors in
modeling performance even when the conceptual
prepresentation is accurate. Therefore, the poorly
learned subskills Of complex behaviors must first be
independently refined through modeling and guided practice.

Motivational subprocess pertains mainly tO
reinforcement. Bandura (1986) emphasized the distinction
between skill acquisition and performance due to a positive
incentive. Although individuals may possess the ability
to perform modeled activities, they may not do SO until
positive incentive is provided. Reinforcements are
divided into three types in Bandura's explanation. Direct
reinforcement occurs when an Observer watches a behavior
being modeled and imitates the modeled action. Positive

or negative reinforcement from the model can occur.

28
Vicarious reinforcement occurs when an Observer watches
other individuals being reinforced for a particular
behavior. Self-reinforcement is the last type Of
reinforcement and is behavior that is enacted in order tO
meet personal standards rather than for the approval Of
others such as teachers or peers.

In this study, it was Of interest tO investigate
whether using a similar model in wheelchair tennis would
affect learning Of the tennis serve for beginning wheelchair
tennis players. Therefore, the literature reviewed in the
next two sections was about the effects Of model
characteristics and model similarity.

Effects Of Model Characteristics

Many studies have investigated the effects Of model
characteristics on motor behavior (Feltz, 1982; Feltz &
Landers, 1977; Feltz, Landers, & Raeder, 1979; George,
Feltz, & Chase, 1992; Landers, 1975; Landers & Landers,
1973; Lirgg & Feltz, 1991; Martens, Burwitz, & Zuckerman,
1976; weiss, Ebbeck, & Rose, 1992; Wiese-Bjornstal, & Weiss,
1992). Landers and Landers (1973) investigated the
influence Of model status and ability level on children's
motor performance. Subjects (3:100), 10— to 12—year-Olds,
were randomly selected. Several factors were examined:
model type (teacher vs. peers), the model's ability (skilled
vs. unskilled), and the model's presence (present vs.

absent). Subjects receiving these eight conditions (g= 10

29

in each group) were additionally compared tO a control group
(g?20) which did not receive any model demonstration. The
motor task used was a free-standing balance ladder designed
by Bachman (1961). Each subject was given 30 trials with
a 10 second rest after trials 10 and 20. The score
recorded was the last prOper consecutive rung Obtained on
the ladder. Subjects listened tO tape-recorded instructions
before a live model demonstrated the task. NO
demonstration was provided for the control group after the
tape-recorded instructions. Results Of the repeated
measures ANOVA indicated that modeling facilitated skill
acquisition better than no model. In post hoc analysis Of
the model type x model's ability interaction, subjects
viewing a skillful teacher model performed significantly
better than subjects viewing an unskillful teacher model or
subjects viewing a skillful peer model. Subjects who
viewed an unskillful peer model performed significantly
better than subjects who viewed an unskillful teacher. In
the conclusion Of Landers and Landers' study, effects Of the
model were significant by model's type, ability, and
presence.

Landers (1975) investigated whether temporal Spacing of
a demonstration and audience presence affect learning on the
Bachman ladder task. Subjects (y;180), 11- to lZ-year-Old
girls, were randomly assigned tO one Of six experimental

conditions. Model presentation consisted Of three types

30
Of temporal spacing including before performance,
interspaced before and midway, and midway only. Audience
types were experimenter only, model audience, or stranger
audience. Successful performance on the free-standing
Bachman ladder was measured by the number Of rungs
successfully attained in a trial. Each subject was
provided 30 trials with a 1-minute rest after 15 trials.
Results indicated that subjects' performances improved in
the before and interspaced conditions as compared to the
midway condition. The experimental group with treatments
Of model presentation showed better performance than the
control group. The audience effect was not found in
Landers' study. Landers concluded that a model
demonstration provided before and interspaced through
learning trials was the best temporal Spacing for
Observational learning.

A new pattern Of behavior is acquired through
Observational learning including attention and retention
mechanisms (Feltz, Landers, & Raeder, 1979). Jeffery
(1976) reported that re-enactment Of modeled behaviors was
involved in the attention and retention mechanisms to
execute successful acquisition Of Observed behaviors.
Martens et a1. (1976) conducted a series Of four experiments
tO examine the effectiveness Of Observing (a) a correct
model, (b) a model progressively improving on the task

(learning sequence model), and (c) an incorrect model in

31
the initial acquisition Of two motor skills. Two
different age groups, second and third grade boys, and
seventh and eighth grade boys, performed two motor skills to
investigate the influence Of Observing the three different
model types. The results indicated that the Older boys
performed better than younger boys. The correctly modeled
group and learning sequence modeled group performed better
than the incorrect modeled and control groups in the first
10 trials Of a motor task that required rolling a small
black ball up an inclined board. Those two groups
conveyed the best information about the force tO be applied
on the ball. Also, they found that there were nO
differences in motor performance between the live model
group and the filmed model group.

The importance Of a model's presence was reported by
Landers and Landers (1973). The model's presence was a
influential force and a great incentive for Observers'
achievement on motor behavior. Similar to the conclusion
Of Landers and Landers (1973), Feltz and Landers (1977)
indicated the importance Of viewing a demonstration. In
their findings, Students receiving a model demonstration had
higher performance scores than students not given a model
demonstration. Feltz and Landers (1977) investigated the
effects Of the informational and motivational components Of
a model's demonstration on motor performance Of a Bachman

ladder task. The effects Of gender on Observational

32
learning was noted as a secondary inquiry. Subjects
(3:80), 40 males and 40 females from 12 fifth- and sixth-
grade physical education classes, were randomly assigned to
treatment groups. Students were compared under the
following four conditions: (a) informational/motivational
cues where a model demonstrated the task and gave verbal
knowledge Of results Of the model's performance on the task;
(b) motivational cues only where no demonstration was
provided; (c) informational cues only where a model
demonstrated the task but gave nO verbal knowledge Of
results Of the model's performance on the task; and (d) nO
cue where no demonstration and no verbal knowledge Of
results were provided. In these conditions, informational
cues came from viewing a demonstration, and motivational
cues derived from knowledge Of results. After initial
instructions, subjects, except the control group, viewed a
videotaped demonstration of their regular physical education
teacher. Subjects were allowed three practice trials
before data were collected. The test consisted Of 30
additional trials. Results related tO the demonstration
effects indicated that the informational component is the
primary factor affecting students' motor performance on the
Bachman Ladder. Students who received a model
demonstration showed higher scores than students not

receiving model demonstration.

33

Feltz (1982) examined the effects Of age and number Of
demonstrations on Bachman ladder performance and form.
Subjects (se120), 60 females in fourth and fifth grade and
60 females in college, were randomly assigned tO four
modeling conditions that consisted Of no, four, eight, and
twelve videotaped demonstrations. Each subject was given
10 trials Of the Bachman ladder task, which was evaluated by
the number Of rungs Obtained and the accuracy Of imitation.
The results indicated that subjects in both age groups whO
received 12 demonstrations showed better performance than
subjects who received fewer demonstrations. In Feltz's
conclusion, the Optimal number Of demonstrations was
emphasized tO create modeling effects. Effects Of model
demonstrations were revealed from the analysis with form
(strategy Of performance). She concluded that form was a
better determinant Of modeling than were performance scores
on Bachman ladder performance and form.

Lirgg and Feltz (1991) replicated the study Of Landers
and Landers (1973), examining the influence Of model status
and ability level on children's motor performance. Female
subjects in sixth grade from a middle school (ESIOO) were
randomly assigned tO one Of five modeling conditions that
included teacher or peer model, Skilled or unskilled model,
and control group. Each subject was given 30 trials Of
Bachman ladder performance after tape recorded instructions.

A self-efficacy questionnaire was completed by each

34
subject. A design of 2 x 2 (Model Type x Model Skill) was
analyzed by MANOVA. The control group (no model) was
compared tO all experimental groups by MANOVA with repeated
measures Of 2 x 6 (Group x Trial Block). The results
regarding model's Skill level supported the results Of
Landers and Landers (1973) that the skilled model group
showed better performance than the unskilled model group.
Otherwise, different effects by model type, teacher model,
or peer model, were not identified in their study. In the
results Of the self-efficacy test, subjects who watched the
Skilled model's demonstration showed higher self-efficacy
than subjects who watched the unskilled model's
demonstration or nO demonstration.

Modeling effects on children's form kinematics,
performance outcome, and cognitive recognition were examined
by Wiese-Bjornstal and Weiss (1992). Female subjects
(ye36), 7-0 tO 8-11 years, were randomly assigned tO one Of
three experimental conditions: (a) a visual model only on
the first three blocks, and a visual model plus verbal cues
on the last block; (b) two blocks Of visual model followed
by two blocks Of visual model plus verbal cues; (c) visual
model on the first block followed by three blocks Of visual
model plus verbal cues. The task was a modified softball
fast pitch. All subjects were tested and tape-recorded
with four blocks Of five pitching trials to be evaluated.

The results indicated that, with repeated Observations Of a

35
model and practice Of a complex sport skill, young girls
Showed improvements in the recognition Of correct form and
matching Of correct form to the model.

Model characteristics that influence the attentional
process include perceived competence and status (Rosenthal &
Bandura, 1978). The more competent a model is perceived
to be, the more likely children will imitate the modeled
action. Higher status persons are imitated more frequently
than lower status persons. In addition, the physical
attractiveness Of a model influences attention. Models
who are interesting and attractive are more Often attended
tO than models who lack attractive qualities (Bandura,
1986).

Useful information tO execute apprOpriate behavior can
be conveyed by Observing a model who can efficiently provide
an exact image that the task demands. In teaching
physical activities, language has some limitations in
describing complex movements. Therefore, a model's
demonstration is essential in teaching motor skills
(Martens, Burwitz, & Zuckerman, 1976). Weiss, Ebbeck, and
Rose (1992) emphasized the importance Of visual information.

In their conclusion, modeling was one Of the most
important instructional strategies for extending the variety

Of physical activity skills for children and adults.

36

Effects of Model Similarity

The effects of Similar models were found by several
researchers (George, Feltz, & Chase, 1992; Gould & Weiss,
1981; McCullagh, 1987). The model similarity between the
Observers and the model can be influential in conveying
cOpying the model's demonstration. Gould and Weiss (1981)
noted the effects Of model similarity in which subjects in a
Similar model group (a model Of same gender and similar
athletic ability) showed better performance on a muscular
leg endurance task than subjects in a dissimilar model group
and subjects in a control group. Subjects (ss150) were
female college students enrolled in a physical education
class, excluding all physical education majors and
intercollegiate athletes. Subjects were randomly assigned
to one Of eight experimental groups, with 15 subjects in
each group and 30 subjects in the control group. The
model's demonstration was provided by two different models.
One is a similar model, a 24-year Old female described as a
nonathlete, the other is a dissimilar model, a 27-year Old
male varsity track athlete. The task was a modified
muscular endurance task in which the subject was required to
hold one leg in a horizontal position for as long as
possible. Sitting on a bench, the subjects held their leg
over a cord Of the same height, attached tO a microswitch
which triggered a timer. Subjects were given three trials

after completing self-efficacy questionnaire which assessed

 

37
their level and strength Of efficacy expectations. At the
end Of the third trial, subjects were given a post
questionnaire which assessed causal attributions and
cognitive strategies used during their performance. The
results showed that subjects in the similar model group
extended their legs Significantly longer than subjects in
the dissimilar model group and control group.

Levels Of self-efficacy also were analyzed in Gould and
Weiss's (1981) investigation. There were significant main
effects with levels Of self-efficacy. Subjects who viewed
a similar model's demonstration scored significantly higher
on the level Of self-efficacy questionnaire than subjects
who viewed a dissimilar model's demonstration. With
strength Of self-efficacy, subjects who were assigned to a
Similar model group were more confident than subjects who
were assigned tO a dissimilar model group. Gould and
Weiss concluded that performance difference between similar
and dissimilar models provided an evidence for a
motivational process. It was argued that modeling is not
only an important technique for conveying task-related motor
performance information but may also play an important rOle
in an Observer's motivation.

In the study Of McCullagh (1987), the rOle Of model
characteristics was examined in an Observational learning
setting. the investigator concluded that the similar

model condition provided a more effective setting for better

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de

an

9X

tl‘u

mot

and

Per:

38
performance after watching a model than the dissimilar model
condition. Undergraduate female students (ys75) were
randomly assigned tO four modeling conditions and one
control group. The scores Of Bachman ladder performance
were analyzed by 2 x 2 x 4 (Model type x Cuing x Trials
Blocks) factorial design. The results indicated that
subjects who viewed a similar model performed better than
subjects who viewed a dissimilar model.

George, Feltz, and Chase (1992) replicated the previous
study Of Gould and Weiss (1981). Female students (E =
100) who were enrolled in introductory psychology classes
were randomly assigned tO one Of four modeling conditions:
(a) an athletic male model; (b) an athletic female model;
(c) a nonathletic male model; and (d) a nonathletic female
model. The model similarity or dissimilarity was
manipulated by the athletic experience. Subjects viewed a
60-second videotaped demonstration Of one Of four models and
performed the same task (leg-extension task) shown by a
demonstration. Results supported the conclusion Of Gould
and weiss (1981) that subjects in the similar model group
extended their legs Significantly longer than subjects in
the dissimilar model group.

Findings of studies related to the importance Of a
model indicate that use Of a model is better than nO model,
and that model similarity has a positive effects on motor

performance. Observers viewing a skilled model showed

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39
better performance than those viewing an unskilled model.
There were age effects in which Older children performed
better than younger children after viewing a model perform
the target task. Regarding the number and timing Of
demonstrations, there were positive effects on temporal
Spacing for modeling when model demonstrations were provided
before and interspaced throughout the learning trials.
The form scores were reflective Of strategy and more
sensitive to modeling effects than the typically used
performance outcome scores. Therefore, form was
identified as a better indicator of modeling effects
compared to the performance outcome scores in motor
performance.
Application of Modeling tO Wheelchair Tennis

What is the best model for instruction in wheelchair
tennis? This is the main question addressed in this
study. As Bandura (1977) mentioned, concerning the role
Of modeling in sport skill acquisition, people learn new
patterns Of movement by Observation. When we imitate a
new movement in sport skills, the encoded coordinates do not
match any that are associated with previously stored
representations Of movements (Christina & Corcos, 1988).
The beginning wheelchair tennis players, the subjects Of
this study, will learn tennis serve which is a new movement
for them. Thus, the encoded body-centered coordinates

themselves will be sent to the instructions generation

40
subsystem. The identity and order Of the individual
movements are stored in associated memory, which then can be
used by the instructions generation subsystem tO produce the
movements in that order (Kosslyn & Koenig, 1992).

The pioneering Russian physiologist Bernstein (1967)
suggested that when learning a new action, one Often encodes
several subgoals that only approximate the action. Hence,
when one later produces the movement, one may lock joints
together which simplifies the problem Of generating movement
instructions on the basis Of what has been encoded.

As more individual movements are composed into an
action, the action will necessarily be increasingly
imprecise; one has never combined the movements in this way
before, and SO the sequence has not been tuned for the
prOperties Of the limbs used to perform it (Christina,
1987). Thus, the wheelchair tennis serve for beginners
requires a critical use Of the movement monitoring subsystem
to imitate the modeled tennis serve motion.

In conclusion, the modeled acts in wheelchair tennis
are the important cues for wheelchair tennis learners'
attentional subprocess to mimic the tennis skills. There
should be differential effects between the stand—up model
and the wheelchair model on the acquisition Of the

wheelchair tennis skill by wheelchair users.

41
Description Of the Tennis Serve

The tennis serve is the stroke that puts the tennis
ball in play and Often is referred to as the most important
stroke in the game of tennis. It has become a primary
weapon Of attack and is used to place the Opponent on the
defensive by forcing a return from the weak Side or by
moving the receiver out Of position. Gensemer (1975)
Observed several professional tennis players for whom more
than 50 percent Of the points in a match were scored as a
direct or indirect result Of the serve, and estimated it was
therefore reasonable tO expect tO win at least 75 percent Of
the games that such a player serves. Gonzalez (1985)
suggested that there were several key techniques one should
utilize to ensure a gOOd serve. In his conclusion,
extending the arm fully would help create more force. A
continuous, loose motion, hitting up, into, and through the
ball are necessary for an effective serve.

The serve provides the one Opportunity for the
performer tO be in absolute control Of the body, the ball,
and the Opponent. A gOOd serve can be described as a ball
hit forcibly and placed strategically in the Opponent's
serve court (Driver, 1970). Further descriptions Of the
serve include the strategies Of varying ball speed,
placement, and spin. These strategies, however, usually
are found in the performance Of more advanced tennis

players. In reviewing the tennis serve techniques in this

42
study, the instructional cues for tennis serve were

described to help beginners perform the tennis serve.

Stand-up Tennis Serve Technigue

The stand-up tennis serve was defined as a serve
performed by a player whO is in a standing position. The
technique of the stand-up serve, the typical serve in a
tennis game, is described by the parts in detail such as
grip, stance, ball toss, backswing, forward swing tO
contact, follow-through, and the motion Of the body.
spip

The grip most Often recommended tO beginners is the
forehand grip. With this forehand grip, the face Of the
racket becomes an extension Of the palm Of the player's
hand, wrist, and forearm (Yandell, 1990). In the serve
grip, the bottom Of the base knuckle Of the index finger
lies on the tOp back bevel Of the racket. The fingers are
spread and the thumb is wrapped around the handle. The
grip is relaxed, not tight (Johnson & Xanthos, 1988).
Stance

The feet are kept separated about shoulder-width apart
during the serve. When serving to the right serve court,
a sideways-position is taken to the net, three or four feet
to the right Of the center mark behind the baseline. The
front foot is two to three inches behind the line, the toes
pointing toward the right net post. The back foot is

parallel to the baseline (Johnson & Xanthos, 1988). The

43
weight is equally distributed on both feet, and the knees
are slightly flexed (Yandell, 1990).

The toes Of the front foot are kept in contact with the
ground throughout the serve, moving the foot only after
contact has been made. The momentum Of the racket pulls
the performer into the court. Keeping the foot on the
ground will give the beginner a firm base from.which to hit,
and at the same time, will eliminate possible foot faults
(Johnson & Xanthos, 1988).

Ball Toss

The ball toss is the key tO a well-executed serve.
Without a gOOd toss, it is impossible tO hit the serve
correctly; therefore, the toss is the most important and
difficult Obstacle for beginners in tennis play (Yandell,
1990). When the arm and racket are fully extended, the
released ball should reach a peak higher than the tip end Of
the racket. A gOOd release consistently places the ball
in the prOper hitting position. Tossing and lifting the
ball for the serve also involves technique as well as
placement. The ball is held in the fingers Of the hand,
palm up; the ball tO be tossed is held by the thumb, index
and middle fingers. The ball is placed in the air by an
extension Of the arm and hand, ending in full extension
forward Of the shoulder. The ball should be tossed with
little or nO spin. Keeping the fingers extended will

prevent hooking the toss, which leads tO loss Of control

44
(Johnson & Xanthos, 1988). The shoulder should remain
perpendicular to the net while tossing the ball. The
tossing arm is straight and dropped straight down tO the
front Of the front leg on the hinge Of the shoulder
(Yandell, 1990).
B_ac_=lt_8£i_ng

The backswing begins with the racket out in front Of
the body, pointing toward the target, about chest high, and
with the non-racket hand holding the ball against the racket
strings. As ball toss begins, the arm and racket begin
the downward swing with the edge Of the racket head leading.
If the timing is not right, it is better to stop the swing
and start again (Brown, 1989).

The racket arm moves down, then into the "back-
scratching position" while the other arm begins tO move up
to lift the ball for the toss. There should be rhythmic
feel to the serving motion. When the elbow reaches a
position slightly higher than the shoulder, the elbow bends
and the racket head drOps down behind the back into what is
called the "back-scratching position," the racket head
pointing straight down to the ground. It is important tO
practice the down-together-up-together coordination Of the
ball toss and racket arms until it is smooth and consistent

(Johnson & Xanthos, 1988).

45
Forwsrd Swing tO Contact

The wrist and elbow snap the racket head upward and
forward with full extension Of the body to contact the
tossed ball. The shoulders and trunk rotate forward to
make the weight shift. TO make the most Of the weight
transfer, the feet change position during the motion. As
the body leans forward, the foot closer to the line stays in
the same place, but the other foot goes forward. The back
foot is moving forward to a point just behind the front foot
prior tO ball contact (Brown, 1989).

High contact is crucial tO the serve motion. It
ensures maximum net clearance and imparts the correct
trajectory so that the ball lands consistently within the
Opponent's serve box. High contact also maximizes body
leverage, and is a major factor in shot velocity. The
great serves are extended at the contact from the tip Of the
toes to the tip Of the racket (Yandell, 1990).
Follow-Through

The follow-through is not down but up and out; the
racket moves up and forward. After contact, the racket
continues forward (toward the net) as far as it can go.

It continues with the head Of the racket swinging freely
past the other side Of the body. The back foot swings
across the baseline and continues forward, taking a step in

the direction Of the serve to help maintain balance and

46
continue the player's momentum. Later it will become the
first step in player's approach to the net.
Trunk Rotation

A lOt Of angular momentum is created by trunk rotation
in the tennis serve. However, it is difficult to employ
this excessive trunk rotation efficiently and still be able
to sequence the rest Of the motion prOperly. If players
are not used tO this motion, they might hurt their backs
(GrOppel, 1992).

Yandell (1990) indicated a common error on the serve
motion; namely, that beginners tend tO bend at the waist
during follow-through. This is a result Of trying to
overhit the ball by throwing the shoulders forward in the
course Of the hitting motion. Instead Of additional
power, the bend results in a lower contact point and less
net clearance. TO correct and prevent bending at the
waist, one needs to adjust the upper body until standing
straight up and down from the waist after trunk rotation.
Upper Limb Motion

By the time the trunk reaches its peak rotational
velocity, the swinging arm should have gone through all Of
its preliminary actions and should be ready for the forward
swing. When the arm is in its backswing position, it is
rotated at the shoulder. As the forward swing takes place,

the upper arm internally rotates at a high rate of speed

(GrOppel, 1992).

47

Elbow Action

Elbow action takes place next as the player accelerates
the racket head toward the point Of impact. GrOppel
(1992) noted that the elbow action is necessary for a good
serve. Two types Of motion were explained in the elbow
action, extension from the flexed position attained in the
backswing, and pronation Of the hand and forearm. Because
the velocities for these two movements are extremely high
and combined with its fragile joint structure, the elbow
joint is quite vulnerable tO injury.

Wheelchair Tennis Serve Technigue

The wheelchair tennis serve is characterized by using
the upper body only. The technique Of the wheelchair
tennis serve is derived from the regular tennis serve form
and technique which is related tO upper body parts. The
techniques Of ball toss, upper limb motion, and elbow action
are exactly like the technique Of stand-up serve, but other
components Of the serve are slightly modified for the
adaptation to the wheelchair tennis serve technique.

As tO grip techniques, quadriplegics Often lack ability
to grip a tennis racket effectively. There are several

ways to aid a student with limited or no hand function in

holding a racket. The most common way is by wrapping the
hand with a ace bandage. The tape is used tO secure the
player's grip. For the serious player, polyethylene

devices molded to fit the hand, and which fasten to the

48
racket handle are available (AAHPERD, 1991; Paciorek &
Jones, 1994). TO move after the tennis ball is served,
the wheelchair user must learn to grip the racket and push
the rim of the wheelchair with the same hand. A
wheelchair user can take hold Of his/her racket using
his/her fingers which overlap the grip to hold the push rim.
This allows a wheelchair user tO maneuver the chair and
prepare for the next step to hit the returned tennis ball
more quickly (Parks, 1980).

For correct wheel position technique, the two wheels
are in a position sideways to the net about 45 degrees, with
the upper body facing one Of the net posts. In the case
Of a right-handed player, the left wheel is forward closer
to the net. If left-handed, the right wheel is forward
closer tO the net. When serving to the right court, the
wheelchair is set three or four feet to the right Of the
center mark behind the baseline. When serving tO the left
court, the wheelchair is set three or four feet tO the left
Of the center mark behind the baseline (Parks, 1981).

The ball toss in wheelchair tennis is the same as the
technique Of ball toss in stand-up serve. The only
difference from stand-up serve is that the tossing hand
grabs the wheel for balance after tossing the ball (Parks,
1981).

Usually, the arm and racket begin the downward swing

with the edge Of the racket head leading as the ball toss

49
begins. But, the downward swing is hampered by the
sitting position in a wheelchair; therefore, Brown's (1989)
punch serve technique is apprOpriate for the wheelchair
tennis serve. The punch serve is started by the prepared
backswing. Before the toss, "scratch your back" with the
racket is performed by touching the middle Of your back with
edge Of the racket. Wheelchair users with higher levels
Of spinal cord injuries who have poor balance may also have
a better chance to perform tennis serve with the racket
behind the back, rather than taking a full swing (AAHPERD,
1991).

It is important that the serving motion goes up at

first rather than forward after the toss. The arm and
racket Should be fully extended when contact is made.
The hitting height in the wheelchair tennis serve is lower
than in the standing serve; therefore, full extension Of the
arm and racket is more important to a successful serve in
wheelchair tennis than in the stand-up serve. Because the
racket should not hit down on the ball, the racket moves
upward and outward. This motion requires the body weight
transfer with one step forward for stand—up serve, but
wheelchair tennis players may lean the upper body back and
forward instead Of stepping tO shift body weight (Parks,
1981).

The initial action Of the follow—through is the same as

the technique for the Stand-up serve, but the rest Of the

50
follow-through should be across the front Of the upper body,
ending above the Opposite wheel from which the motion began.
The solid hit and straight follow-through is much better for
wheelchair users to perform wheelchair tennis serve at
beginner's level (8. DrObac, personal communication, April
8, 1994).
Methods Of Assessing the Tennis Serve Technique
Assessment Of Biomechanical Variables

Tennis has develOped through years Of trial and error.
Few groups Of scientists, engineers, and players have ever
attempted to determine the underlying scientific principles
Of the game and then to construct strokes and strategies
based on their analyses.

The techniques Of human movements are the major concern
Of biomechanics. Therefore, one might expect a great deal
Of biomechanics research activity tO be concerned with the
effects of technique on teaching tennis performance.
However, few scientific studies have been reported in which
biomechanical analyses Of tennis performance related tO
teaching methods were conducted. The study by Holcomb
(1963), which was regarded as an early scientific trial, was
concerned with the application Of biomechanical principles
in analyzing tennis strokes.
Ball Velocity

Ball velocity is one of the important components Of an

effective tennis serve. Although several sources are

51
cited, results are not necessarily comparable because Of the
different methods used in the determination Of the velocity.
Male tennis players (§:13) were tested tO measure ball
velocity by Plagenhoef (1970). Their serve ranged from a
low Of approximately 71 miles per hour tO a high Of just
over 100 miles per hour. Determination of these
velocities was based upon film measurements in which camera
speed was set at 64 frames per second and a 1/4 shutter
factor provided an exposure time Of 1/512 second.

Using a special radar device develOped by the
Massachusetts Institute Of Technology, the serve velocity Of
both men and women professional players was determined by
Cubbedge (1977). Ball velocity Of 133 miles per hour was
the fastest serve for a man and 102 miles per hour was the
fastest serve for a woman.

SebOlt (1969) investigated the ball velocity Of college
men. The mean serve velocity for the 40 subjects was
87.91 feet per second with a standard deviation Of 14.33.
While studying a group Of college men whO were beginners in
tennis, he found a positive relationship between maximum
serve velocity and playing ability.

The ball velocity Of college women was investigated by
Schrader (1972). She used a 10-pOint velocity rating
scale in which the size Of the scale intervals was based
upon the serve velocity scores Of 576 subjects who were

beginners in tennis. These velocity scores had been

52
computed by the time-distance method. The highest score
interval included those serves with a velocity Of 63 feet
per second or greater and the lowest score interval
contained those serves with a velocity Of 39 feet per second
or less.
Racket Velocity

The velocity Of the racket head at ball/string impact
point was determined by Plagenhoef (1970). The velocity
Of the racket head ranged from 56.5 tO 85.5 miles per hour.
From his investigation, as racket velocity increased, the
server faced greater difficulty in holding the racket
firmly, and therefore ball velocity would decrease.

Angle Of Projection

Effectiveness Of the serve is also dependent upon the
angle at which the ball is projected from the racket
strings. If the height Of racket/ball contact remains
constant and Optimum racket velocity is achieved, the angle
Of projection is viewed as the critical factor in
determining the successful serve.

Owens and Lee (1969) used various combinations Of
variables tO determine successful serves. They reported
the minimum and maximum angles Of projection Of a served
ball based upon heights Of racket/ball contact, ball
velocities, and net clearance. Angles Of projection
varied from -5 degrees tO +15 degrees from the horizontal.

Beginning tennis players Should be instructed tO contact the

53

ball at an angle Of zero degrees to the horizontal for a
more successful serve (Broer, 1973). I
Center Of Gravity

Determination Of total body center Of gravity indicate
where the body weight Of the server is located and how the
transfer Of weight is occurring during the serve motion.
Although there was disagreement concerning the server's
weight distribution in the starting position, the player’s
weight is primarily on the rear foot at some point during
the serve. Also, there was a consensus that the weight
must transfer or shift to the front foot before the time Of
racket/ball contact (Smith, 1979).
Ground Reaction Forces

Payne (1974) studied the kinetic ground reaction
forces, which were produced by the tennis player during the
execution Of the serve motion. In this study, two Square
force platforms were positioned under the subject's feet,
but the result Of the study gave no indication about the
match Of the force data and film data. Payne (1974)
explained that the complex shifts Of body weight in the
tennis serve seemed to limit the use Of the force platform
results tO that of force-trace comparisons.

Field Tests for Tennis,Serve Performance

What is a gOOd serve and how can the serve be evaluated

for the wheelchair tennis player? Even though there was

little literature relating to the methods Of assessing

54

wheelchair tennis skill, the tennis literature contains
numerous tests Of tennis ability with varying degrees Of
validity and reliability. A good serve in the game Of
tennis is described in the terms Of three components which
are ball velocity, ball placement, and spin of the ball
(Driver, 1970). Although the spin is regarded as an
important component of the serve, nO accurate and practical
method for assessing Spin has been developed. In the
tennis literature, the spin was mentioned least Often in
describing a gOOd serve for the beginners. It is also
questionable that introduction to the component Of spin
before mastery Of ball placement and ball velocity is prOper
(Ballard, 1973). Therefore, ball velocity and ball
placement were selected by the investigator tO assess the
beginners' serve technique in a wheelchair tennis.
lel Vslocitv

The velocity Of the serve in CObane's (1962) test was
measured by the zone Of the second bounce. This method
was based upon the theory that the higher the velocity Of
the ball, the greater the distance Of the bounce. The
zones were divided beyond the base line. When 24 serves
were used, the test had a recorded reliability Of .87.
Cotton and Nixon (1968) used this same concept to measure
velocity in their serve test. Hewitt (1966) divided the
area of the court beyond the service line by four zones.

The first zone was back court area to the baseline. The

55
second zone was 10 feet beyond the baseline. The third
zone was 10 tO 20 feet beyond the baseline. The fourth
zone was the area 20 feet beyond the baseline or the fence
in most instances. The second bounce into the area
indicates the velocity Of serve. Avery, Richardson, and
Jackson (1979) also used the zone Of the second bounce in
their service test.
Placement

The method Of assessing placement Of the tennis serve
was indicated by hitting the target area in the serve box.
The subjects were required to serve tO a target on the
court. The targets were varied with reSpect tO size,
shape, and placement on the court. In Hewitt's (1966)
test, points are assigned to target areas, and serves
landing in these designated areas receive the points
assigned tO that area. The validity coefficient Of
Spearman Rho was .72 in Hewitt's serve test and the
reliability Of serve placement test was .94. O'Donell
(1956) also divided the service box into zones Of different
values in the serve test. The reliability Of the test Of
O'Donell was .65.

In summary, biomechanical variables such as racket
velocity, angle Of projection, center Of gravity and ground
reaction force have been used tO describe motion
characteristics. The achievement test in tennis

performance was measured through various field tests

56
including ball velocity, ball placement and spin. Ball
velocity is one variable which is related to the
biomechanical factor; therefore, the ball velocity can be
measured by using biomechanical equipment in the field test.
Ball placement can be measured by means Of the ball
placement component Of Hewitt's serve test.
Conclusion

With instructional emphasis in individual skill
development, the primary method which physical educators use
to teach new sport skills is visual demonstration or
modeling. Modeling is a general process in which
Observers attempt tO reproduce the actions demonstrated by
another person. The importance Of the serving tennis ball
is regarded as an important role in wheelchair tennis game.
In teaching tennis Skill, modeling is essential for a novice
tO acquire tennis serve skill. Therefore, modeling
effects could be produced by teaching wheelchair tennis
serve skill using demonstrations by different models.

Experts in measurement agree that skill testing is used
mainly for grading, classifying, guiding, and motivating
students, as well as for furthering research. A skill
test also provides a procedure for measuring the
effectiveness Of the program, the methods Of instruction,
and the instructor. Criteria for selecting and developing
tests Of skill include technical as well as practical

standards, and technical criteria such as validity,

57
reliability, and Objectivity should be determined. A test
which is technically correct but is impractical in that it
requires expensive equipment, is time consuming to
administer, or scores are difficult to compute usually must
be rejected or revised. Therefore, a field test is
preferred to measure the performance level in wheelchair
tennis serve Skill rather than a biomechanical evaluation.
The Hewitt Tennis Achievement Test showed the highest
validity and reliability among the field-based tennis
performance tests that were reviewed. Regarding the
measurement Of ball velocity in the Hewitt Tennis
Achievement Test, a radar device is recommended tO improve

the accuracy Of the test.

CHAPTER I I I

STUDY 1

Methods
Research Design

Independent Variables

The purpose Of Study 1 was tO determine whether test
performance in the wheelchair tennis serve was influenced by
type Of model; namely, demonstration by a model seated in a
wheelchair versus demonstration by a model standing erect.
Therefore, the type Of model (wheelchair, stand-up, and nO
model) was the independent variable in this study. All
demonstrations were performed by the investigator and
videotaped for presentation tO the subjects.
Dependent Variables

There were three dependent variables in this study: (a)
the form score Of the wheelchair tennis serve; (b) the ball
velocity Of the wheelchair tennis serve; and (c) the
placement score Of the wheelchair tennis serve. The form
score Of the wheelchair tennis serve was the percentage Of
correctly performed steps out Of a possible 16 steps for the
form evaluation across 10 serves. The form evaluation was

based on a checklist Of the wheelchair tennis serve

58

59
(Appendix C). The velocity Of the served ball was
measured by a Speed gun. The placement score Of the
wheelchair tennis serve was the percentage Of points earned
by the number Of successful serve placements across each
block Of 10 serves.
Experimental Design

The design was a pretest-posttest randomized groups
design (pretest, then learning trials, then posttest).

Each subject was randomly assigned tO one Of three treatment
conditions: (a) a wheelchair model who performed the tennis
serve while in sitting a wheelchair; (b) a stand-up model
who performed the tennis serve while in standing position;
(c) nO model. Each subject was tested by (a) serve form,
(b) ball velocity, and (c) ball placement as dependent
measures. A diagram Of the experimental design is
illustrated in Figure 1.

The selected model was the investigator who is a
skilled tennis instructor. Landers and Landers (1973)
indicated that the skilled model group showed better
performance than the unskilled model group. Thus, the
model's performance was evaluated by an expert coach Of
wheelchair tennis, Mr. Stan Drobac, to determine whether the
Skill level Of the model was acceptable for teaching
wheelchair tennis serve. The letter Of support from Mr.

Stan Drobac is presented in Appendix B.

60

 

 

 

 

 

 

 

 

Pretest Intervention Posttest
Wheelchair 10 serves . 6 demonstrations 10 serves
model . 10 serves
demonstra- . 6 demonstrations
tion . 10 serves
. 6 demonstrations
Stand-up 10 serves . 6 demonstrations 10 serves
model . 10 serves
demonstra— . 6 demonstrations
tion . 10 serves
. 6 demonstrations
NO model 10 serves . instruction 10 serves
. 10 serves
. instruction
. 10 serves
. instruction

 

Figure l. A diagram Of experimental design for Study 1

 

61

The able-bodied investigator was selected as a
wheelchair model rather than a person with disability so
that the same model could provide demonstrations in both the
wheelchair and stand-up experimental groups.

Rationale for Experimental Design

The pretest and posttest were conducted tO investigate
the effects Of model type in learning the wheelchair tennis
serve Skill. Random assignment was used to distribute the
idiosyncratic characteristics Of the subjects over the three
treatment levels so that they would not selectively bias the
outcome Of the experiment. The number Of subjects (N =
45) was determined to ensure the statistical power Of the F
test over three treatment groups. The number Of subjects
satisfied the minimum sample Size (power = .95, significance
level = .05) determined from the table Of sample Size for
analysis Of variance (Kirk, 1982).

Feltz (1982) indicated that subjects who received 12
demonstrations showed better performance on the Bachman
ladder task than subjects who received fewer demonstrations.
Regarding the timing Of demonstrations, the best temporal
spacing for Observational learning occured when model
demonstrations were provided before and interspaced through
learning trials on the Bachman ladder task (Landers, 1975).
Therefore, six videotaped demonstrations were interspaced

before, midway, and after serve practice for the subjects in

62
Study 1, which satisfied the Optimal number Of
demonstrations and the temporal Spacing for modeling.

The major purpose Of this type Of design was tO
determine amount Of change produced by the treatment.

This design has the threat tO internal validity Of testing
serve performance; however, this threat tO testing was
controlled by the pretest tO posttest comparison in the
experimental group as well as in the control group (Thomas &
Nelson, 1985).

The maturation threat tO internal validity was
controlled by the time period Of experiment for Study 1.
The wheelchair tennis instruction was delimited by a 30
minute time period that helped tO control this threat.
Instrumentation threat was minimized by calibrating
measurement instrumentations, including the Speed gun.

The threat tO internal validity Of subject selection was
controlled by ANOVA test for the pretest scores Of the
wheelchair tennis serve performance tested by form, ball
velocity, and ball placement (Kirk, 1982). Therefore, the
difference betweeen groups prior tO the treatment was
detemmined by a comparison in the pretest scores. In the
results Of ANOVA test for the pretest scores, there was nO
significant difference between groups in form scores, ball
velocities, and ball placement scores. Mortality was not
a problem given that nO lOSS Of experimental subjects

occured while testing serve performance for Study 1.

63

This design is exposed tO the threats tO external
validity which were identified by Campbell and Stanley
(1963). Most Of these threats except experimental
arrangements can be controlled by random selection Of
subjects (Thomas & Nelson, 1985). TO control experimental
treatment, videotaped demonstrations instead Of live
demonstrations were used tO assure consistent and equal
treatment. Also, an able-bodied individual rather than a
person with disability was selected as a demonstration model
for Study 1. The able-bodied investigator was videotaped
in both the stand-up and wheelchair tennis serves in order
to maximize the consistency in demonstrating the tennis
serve form. Reactive effects Of experimental arrangements
were controlled by the investigator, who used one Of the
outdoor tennis courts at Michigan State University SO that
the experimental setting would be generalizable tO real
world settings for the wheelchair tennis play.

We

Subject Selection Procedure

A minimum Of 45 subjects were needed tO ensure adequate
statistical power. TO protect the integrity of the study,
persons with nO prior tennis experience were selected as
subjects. Because gender is a possible nuisance variable
on dependent measures such as ball velocity (Kirk, 1982),

equal numbers Of males and females were selected.

64

The investigator selected all subjects based on phone
calls or personal contact with students at Michigan State
University. Names and phone numbers were located in the
student directory Of Michigan State University. In the
phone conversation, the names were randomly selected using
the random generation method. The investigator gave his
name, present status as a graduate student, the purpose Of
dissertation, and need Of subjects. Information about
previous tennis playing experience and consent Of
participation was collected from the phone call. If the
student had previous tennis playing experience, the
investigator excused the student from participating in the
Study.

A sufficient number Of subjects was not secured as a
result Of phone inquiries; therefore, the investigator
contacted undergraduate students during university
orientation. The same information was given tO the
students, and the consent Of their participation was ensured
by Signing the written consent form.

Subject Characteristigs

The sample consisted Of 45 able-bodied undergraduate
and graduate students (24 men and 21 women, mean age = 23.4
years) from Michigan State University. Written consent
for participation in the study was Obtained from all
subjects prior tO the experiment (Appendix A). All

subjects were beginners in tennis play without prior tennis

65
experience. Table 1 illustrates the number, gender, and
age Of the subjects.
Assignment Of Subject tO Treatment Groups

A total Of 45 students from Michigan State University
were randomly assigned within gender groups tO one Of three
treatment groups using the random number generator program.
Thus, 8 men and 7 women were assigned tO each treatment
group.

Instrumentation

A checklist instrument tO evaluate form for the
beginning wheelchair tennis serve was developed by the
investigator (Appendix C). Randy Snow (personal
communication, August, 1994), former wheelchair tennis world
champion, demonstrated the wheelchair tennis serve and
described key points for develOping the checklist for the
beginning wheelchair tennis serve. His demonstrations and
instructions were videotaped by the investigator using a
Sharp 8mm camcorder (Model VL-E30U).

The investigator studied the video taped demonstrations
performed by Randy Snow and grouped items Of the wheelchair
tennis serve into catagories. The content Of form
checklist was consisted Of 4 phases: (a) 3 Steps in the
preparation phase; (b) 5 steps in the ball toss phase; (c) 5
steps in the execution phase; and (d) 3 steps in the follow-

through phase.

66
Table 1

Number. Gender. and Age Of Subjects Attending the

 

 

 

Interventions

Age in years
Group p (Gender) M SQ
Wheelchair Model Treatment 15 (8M, 7F) 24.60 8.53
Stand-up Model Treatment 15 (8M, 7F) 24.07 7.20

NO model Control 15 (8M, 7F) 21.47 3.64

 

67

The investigator practiced the wheelchair tennis serve
based on the checklist and video taped his own performance
in the wheelchair tennis serve. The form checklist and a
videotaped demonstration Of the wheelchair tennis serve
performed by the investigator were reviewed by Jongoon Kim
(personal communication, August 23, 1994), a member Of the
dissertation committee who has expertise in racket sports.
Jongoon Kim determined the video taped performance and the
checklist tO be adequate for teaching the beginning tennis
players.

Ball velocity was measured in miles per hour (mph)
using a speed gun. The equipment Of a speed gun (Super
Gun manufactured by CMI Inc., Minturn, Colorado) was
provided by Dr. Gene Brown. The letter Of support from
Dr. Gene Brown is included in Appendix B.

Ball placement was measured by a modified component Of
Hewitt’s Tennis Achievement Test. The ball placement
component was modified for use with the subjects in this
study. The test was modified in the target area Of the

serve court SO that there was nO division Of the serve

court. Therefore, the serve was considered successful if
the ball landed anywhere on the serve court. The serve
court area was 6.4 meters by 4.11 meters. The diagram Of

tennis court was illustrated in Figure 2.

68

 

 

Net post
Double sideline 1')
_§i_n_gl_e sideline
Rightserve court

Center service line

 

10.91311 83.22rn

 

 

 

 

Left serve court

fiWVeVs'IHSfim ‘l'o 'u’o ‘o‘s‘u‘o 'u‘u 's'o 's's's‘."

   

Base ' e

Center
mark

4.11m

 

 

 

Alley

 

 

Figure 2. Tennis court diagram and dimensions.

69
Data-Collection Procedures
Pretest and Posttest in the Wheelchair Tennis Serve
The test protocol was the same for the pretest and the
posttest in the wheelchair tennis serve. The format for
the test was as follows:
(a) Warm-up period
. 3 trials Of ball tosses by the subject.
. 3 trials Of the racket swing.
(b) Test period
. 10 consecutive serve trials by the subject.
Equipment for Serve Test
A wheelchair (Model NO: ACTIONPRT, made by Action
Technology, N. Ridgerville, Ohio) was prepared by the
investigator for use by subjects. Two tennis rackets with
same tension Of string but different grip size, were
provided tO the subjects. The subject could choose one Of
two tennis rackets. Usually, the grip Size Of four and
one half was chosen by the men, and the grip size Of four
and one eighth was chosen by the women in this study. A
basket with thirty new tennis balls was provided for the
serve practice, as well as for the serve placement test.
A clipboard, data collection sheets, and pen were provided
tO the assistant who recorded the results Of the performance
on the test. A camcorder, Sharp 8mm Viewcam (Model NO:
VL-E30U), was set by the post Of the net on the tennis court

to record the subject's form during the serve. The speed

70
gun (Super Gun, manufactured by CMI Inc., Minturn, Colorado)
was Operated by an assistant who recorded the velocity as
well as the score on the test for serve placement. The
data collection setting on the serve test court is
illustrated in Figure 3.
Tsst for Serve Form

All subjects were filmed using a Sharp 8mm camcorder
(model VL-E3OU) and 8mm Scotch videotape (model P6-120)
during all tests Of serve form at one Of the outdoor tennis
courts at Michigan State University. Each subject's serve
performance was analyzed using a Sony video cassette
recorder (model SLV575—UC). The investigator played the
recorded tape for serve form in the slow motion function
while evaluating the subject’s form.

The investigator marked each case where the subject
correctly performed the step as the checklist required. A
percentage was calculated as a function Of correctly
performed steps out Of a possible 16 steps. The form
score was the averaged percentage across 10 serves in each
block Of trials.

Isst for Ball Velocitv

A data-collection assistant measured ball velocity
during the ball flight after each serve using a speed gun,
and recorded the result Of ball velocity Of each serve.

The assistant pointed the speed gun toward oncoming ball.

The position Of a speed gun is illustrated in Figure 3.

Double sideline

71

Net post

 

Sin . le sideline
1

 

 

Right serve court

 

 

 

 

 

 

 

 

........ B use . e
, .1; Center service line """"""

' eelcheir ..2=% '15,.

¢ Lett serve court?" Speed nun

Alley "ft
6
Serve position [
Camcorder

Figure 3. Data collection setting on the serve court.

72
Ball velocities were averaged across the 10 serves in each
block of trials.
Isst for Serve Placement
The score Of serve placement was either 1 or 0
depending on the placement Of the served ball: gOOd serve or
fault serve. The successful serve was recorded as 1 and
the fault serve scored as N (below the net), W (wide from
the serve court), and L (long from the serve court). N,
L, or W were equal tO 0 point as the fault serve. A
sample data collection form is located in Appendix C.
Subjects were given 10 consecutive trials Of the wheelchair
tennis serve by the center mark and behind the baseline.
The score ranged from 0 tO 10 depending on the number Of
successful serves out Of each block Of 10 trials. The
score was transformed into the percentile ratio in the raw
data. Therefore, the percentage was determined by the
number Of successful serves (score = 1) out Of 10 serves.
Intervention
Typical Intervention Session
A total time Of 30 minutes was provided for the
wheelchair tennis serve intervention. The intervention
session was classified by demonstration and practice phases:
(a) 6 Observations Of a videotaped demonstration; (b) 10
trials Of serve practices; (c) 6 Observations Of a
videotaped demonstration; (d) 10 trials Of serve practices;

and (e) 6 Observations Of videotaped demonstration. The

73
videotaped demonstrations were divided by three frontal
views and three side views Of a model's serve performances.
During the subject's practices, the investigator provided
verbal feedback tO the subjects based on the model's
performance.

The intervention was conducted between the pretest and
posttest Of the wheelchair tennis serve. Two experimental
groups (a wheelchair model condition and a stand-up model
condition) received the videotaped demonstrations, and one
control group received nO demonstration. The model in the
videotaped demonstrations was the investigator, himself.
The demonstrations in both types Of tennis serve, stand-up
serve and wheelchair tennis serve, were filmed. A
quantitative description Of the model's performance is
provided in Table 2.

Verbal Instruction

Verbal instruction emphasized criteria from the form
checklist for the wheelchair tennis serve. Verbal
instruction preceded every 10 serve trials Of practice and
testing. Verbal instruction was used to describe the
pattern Of the wheelchair serve motion. The investigator
read written instructions about the tennis serve tO each
subject, SO as tO eliminate inconsistencies in verbal
instruction across the subjects. The written verbal

instruction was as follows:

74
Table 2

Description Of Model'ssPerformance in Tennis Serve Tested by

Three Dependent Measures

 

 

Velocity Placement Form
Serve (AVG mph) (%) (%)
Wheelchair Tennis Serve 61.6 50 100

Stand-up Tennis Serve 73.9 70 100

 

75

"Now are you ready for listening tO my instruction

on how tO perform your wheelchair tennis serve?

(ensure subject's attention by an answer).

First, set your wheelchair at about a 45 degree

angle to the net. Hold your racket, and now

scratch your back with the racket, with your
elbowup. Toss the ball straight-higher than you
can reach with your racket. Extend your arm in

the direction you want tO hit. The ball should

gO up without much Spin. AS you hit, your

racket moves up and forward. Extend your arm

when contact is made. Keep your eyes on the

ball. After hitting the ball, continue your

swing and finish on the Opposite Side from where

the swing started. That is all. Now, can you

try out?"

Additionally, verbal feedback was provided following
every block Of 10 serve trials for both the practice and
test sessions. The importance Of ball placement and ball
velocity was emphasized by verbal feedback. The
investigator said, "Your served ball should successfully be
placed on the serve court because a point cannot begin
without a successful serve. And, ball velocity is very
important because the fast serve give you more chance to

have a point than the slow serve." Also, the part Of

76

verbal instruction that the subject could not perform
correctly was presented via verbal feedback.
Types Of Models
Intervention by the types Of models is illustrated in Table
3. TwO types Of models (wheelchair model and stand—up
model) were provided for experimental treatments and nO
model was provided for the control group.

Wheelchair model. Each subject was Offered a total
Of 18 videotaped demonstrations Of the wheelchair model’s
performance Of the wheelchair tennis serve. The
videotaped demonstrations consisted Of six consecutive serve
forms, three each from the frontal and side views. Each
subject received verbal instruction and viewed the six
videotaped demonstrations prior to 10 consecutive practice
serves. Verbal feedback was provided subsequent tO the 10
practice trials. Instruction and Six videotaped
demonstrations were provided after verbal feedback, followed
by another 10 tennis serves. Finally, instruction and six
videotaped demonstrations were provided after the second 10
practice trials, then the subject was tested for the
posttest. Therefore, each subject received a total Of 18
demonstrations and 20 trials Of serve practice.

The 3-inch screen Of the Sharp Viewcam (Model NO: VL—
E30U) was used tO Show the videotape Of a model's
performance. The number Of demonstrations by the

videotaped model and the number Of practice trials by a

Table 3

77

Intervention by the Typessof Models

 

Type Of model

Intervention (30 min.)

 

Wheelchair model
and

Stand-up model

Verbal instruction
Videotaped demonstrations
10 serve practice

Verbal feedback

Verbal instruction
Videotaped demonstrations
10 serve practice

Verbal feedback

Verbal instruction

Videotaped demonstrations

 

NO model

Verbal instruction
10 serve practice
Verbal feedback
Verbal instruction
10 serve practice
Verbal feedback

Verbal instruction

 

78

subject were the same for each subject tO ensure standard
intervention conditions for all subjects. The
investigator ensured each subject's attention before a
demonstration by a question such as, "Are you ready?"

Stand-up model. The videotaped demonstrations by a
stand-up model were shown to the subjects who were assigned
tO the stand-up model condition. Each subject was Offered
a total Of 18 demonstrations by the videotaped model and
verbal feedback by the investigator. Intervention
procedures were identical tO the wheelchair model condition
(Table 3). The videotaped demonstrations consisted Of six
consecutive serve motions which were divided into three
frontal views and three side views. Each subject was
allowed to practice a total Of 20 trials Of the wheelchair
tennis serve during the intervention session. A total Of
18 videotaped demonstrations was presented tO each subject.

NO model. NO demonstration was provided for the
subjects who were assigned to the nO model condition.
Verbal instruction without videotaped demonstrations was
given prior tO each 10 consecutive serve trials for the
practice and posttest. The motion Of the wheelchair
tennis serve was explained by the investigator's verbal
description (see page 73-75). Attention Of the subject
was ensured before verbal explanation was given. Verbal
feedback was provided by the investigator following each

practice session (10 consecutive serve trials). The total

79
number Of serve trials was exactly same in all treatment
conditions.
Statistical Analvsss

ANOVA was used to test the assumption Of equality Of
variance across the experimental groups for the scores on
the pretest. If there were nO Significant differences on
the pretest, ANOVA would be used to test the hypotheses.

If there were Significant differences on the pretest, ANCOVA
should be used to test the hypotheses, with the pretest
score as the covariate.

ANOVA with repeated measures was used to determine the
significant main effects for improvement from pretest tO
posttest and the significant interaction between the types
Of model and test trials. In the case Of significant
differences for the group contrasts on the posttest, Newman-
Keuls multiple post hoc comparisons were performed.
Although there were three dependent variables, ANOVA was
employed for statistical analyses to test the hypothesis
rather than MANOVA, because one dependent variable was
tested by each hypothesis. Also, the investigator was
interested in determining the effects Of model similarity
rather than the relationship between dependent variables.

Since a small subject number was utilized for each
experimental group, the effect sizes (Glass & Hopkins, 1984)
were calculated tO compare the difference Of two means in

posttests between the experimental groups (wheelchair

80
modeled condition and stand-up model condition) and no model
group. Since there was more than one dependent variable,
possible correlations could interfere with ANOVA results.
Therefore, intercorrelations and discriminant analysis were
employed tO determine correlation coefficient and the
discriminant weight in three dependent variables. This
multiple discriminant analysis was used tO compensate for
possible correlations among three dependent variables.
The diagram for statistical analyses is illustrated on
Figure 4.
Results and Discussion for Study 1
Results

The results Of Study 1 have been organized according tO
the hypothesis tested. The statistical analysis supported
the first hypothesis that there would be the greatest
treatment effects for serve form in the wheelchair model
groups compared tO the stand-up model and no model groups.
The statistical analysis did not support the second
hypothesis that there would be the greatest treatment
effects for ball velocity in the wheelchair model group
compared tO the stand-up model and no model groups.
Similarly, the statistical analysis did not support the
third hypothesis that there would be the greatest treatment
effects for ball placement in the wheelchair model group

compared tO the stand-up model and nO model groups.

81

 

Hypotheses

Able-bodied students receiving a videotaped
demonstration by a model who uses a
wheelchair will Show the greatest
improvement in the wheelchair
tennis serve Skill tested by
each dependent measure.

 

 

 

 

 

ANOVA

IS there any difference between groups
on the pretest scores?

 

 

 

 

 

 

NO Yes
1 1
ANOVAS ANCOVA
with repeated Test Of main
measures effects
Test Of main effects

 

 

 

 

 

 

 

 

Is there any difference between groups
on the posttest scores?

 

 

 

l l

 

 

 

 

 

 

Yes NO
1 1
Newman Keuls Effect Sizes
post-hoc Correlations
multiple comparison

 

 

 

 

 

 

 

Effect Sizes

 

 

 

 

 

Correlations
Discriminant Analysis

 

 

 

Figure 4. A diagram for statistical analyses in Study 1

82
Hypothesis 1

The means and standard deviations for form scores for
the wheelchair tennis serve on the pretest and posttest
are presented in Table 4. The pretest scores were
analyzed by ANOVA tO test the assumption Of equality Of
variance across the three experimental groups. The
results revealed that there was no significant difference
among the three groups on the pretest scores, with E (2, 42)
= 0.27, p < .70. Therefore, ANOVA was used rather than
ANCOVA for subsequent data analysis.

ANOVA with repeated measures showed a significant
effect for repeated measures; namely the difference between
pretest and posttest scores, with F (1, 43) = 107.68,

p < .0001. This main effect indicated that all three
groups improved in their scores tested by a form checklist
from pretest tO posttest. A separate ANOVA was conducted
to determine the main effect for model type on the posttest
scores. This main effect was significant, 2 (2, 42) =
5.58, p < .01. A significant interaction was revealed
between model type and test trials for the scores Of serve
form, with g (1, 43) = 10.01, p < .0001. The interactions
between model type and test trials can be seen in Figure 5.

A Newman-Keuls post hoc analysis was employed for the
follow-up method. The results indicated that the
wheelchair model group differed significantly from the

stand-up model group, with Newman-Keuls standardized

83
Table 4
Serve Form Scores (Percentage Of Successful Steps) by

Treatment Condition

 

 

Pretest Posttest
Treatment Condition p M §Q M s2
Wheelchair Model 15 38.45 19.81 74.19 17.50
Stand-up Model 15 35.51 19.10 54.19 17.14
NO Model Control 15 40.85 20.58 53.79 22.27

 

Note. The values represent mean percentages Of correctly

performed steps out Of 16 steps for form checklist.

84

( X Wheelchair HodelO
Stand-up Model El

 

 

No Model B
80
O
70
60
ID
A
50
IL
4 0 .
I
30
I
Pretest Posttest

Figure 5. Treatment condition by trials interaction for

serve form scores (percentage Of successful steps).

85
difference g = 4.04, p < .05. Similarly, the wheelchair
model group differed Significantly from the nO model group,
with Newman-Keuls g = 4.13, p < .05. Inspection Of the
means indicated that subjects in the wheelchair group
improved significantly more than did subjects in the stand-
up and nO model groups. NO significant difference was
detected between a stand-up model group and no model group,
with Newman—Keuls g = .08, p < .98.

In addition tO ANOVA analysis, the effect Sizes were
calculated by standardized mean difference, in which the
numerator was the mean difference between two groups, and
the denominator was the mean for the control group (nO model
group) standard deviation (fig = 22.27). The effect Size
between the wheelchair model group and no model group was
large, with ES = 0.92, which was estimated tO be 0.92
standard deviations. The effect Size between the stand-up
model group and nO model group was small, with ES = 0.02.

A discriminant analysis was employed tO compensate for
possible correlations among three dependent measures. A
Significant discriminant weight with E (2, 42) = 9.20, p <
.001 was Obtained for the serve form scores Of the
wheelchair model group. The subjects receiving a
videotaped demonstration by a wheelchair model Showed the
greatest improvement in serve form compared tO the subjects

viewing a stand-up model or nO model.

86
Hypothesis 2

The means and standard deviations for ball velocity
scores for the wheelchair tennis serve on the pretest and
posttest are presented in Table 5. The results from ANOVA
on the pretest revealed that there was nO Significant
difference among three groups on the pretest scores, with E
(2, 42) = 0.14, p < .89. Therefore, ANOVA was used rather
than ANCOVA for subsequent data analysis.

ANOVA with repeated measures showed a significant
effect for repeated measures, namely the difference between
pretest and posttest scores, with E (l, 43) = 27.69, p <
.0001. This main effect indicated that all three groups
improved in their scores tested by ball velocity from
pretest tO posttest. A separate ANOVA was conducted to
determine the main effect for model type on the posttest
scores. This main effect was not significant, E (2, 42) =
0.95, p < .53. NO significant interaction was revealed
between model type and test trials for the scores Of serve
form, with E (l, 43) = 1.61, p < .21. The trends Of data
from pretest tO posttest are presented in Figure 6.

The effect size (ES) on the posttest between the
wheelchair model and no model groups was negative
(ES = -0.49). The negative effect size indicated that the
experimental group (wheelchair model group) showed a slower
mean velocity Of the served ball on the posttest than the

control group (no model group). Similarly, the effect

87
Table 5

Average Ball Velocities (mph) by Treatment Condition

 

 

Pretest Posttest
Treatment Condition p M §2 M §D
Wheelchair Model 15 31.93 5.76 34.35 7.95
Stand-up Model 15 33.45 9.57 37.18 9.12

NO Model Control 15 32.90 7.91 38.60 8.71

 

88

(mph Wheelchair Model 0
Stand-up Model [J

 

40 No Model 5.
35
30
25
‘ Pretest fi Posttest.

Figure 6. Treatment condition-by trials interaction for ball

velocity.

89
size (ES) on the posttest between the stand-up model and no
model groups was negative (ES = -0.16).
Hypothesis 3

The means and standard deviations for ball placement
scores for the wheelchair tennis serve on the pretest and
posttest are presented in Table 6. The results from ANOVA
on the pretest revealed that there was no significant
difference among three groups on the pretest scores, with E
(2, 42) = 0.10, p < .95. Therefore, ANOVA was used rather
than ANCOVA for subsequent data analysis.

ANOVA with repeated measures showed no significant

effect for repeated measures, namely the difference between
pretest and posttest scores, with E (1, 43) = 0.75,
E < .501. This main effect indicated that none of the
three groups showed any improvement in their scores tested
by ball placement from pretest to posttest. A separate
ANOVA was conducted to determine the main effect for model
type on the posttest scores. This main effect was not
significant, 3 (2, 42) = 2.71, p < .08. No significant
interaction was revealed between model type and test trials
for the scores of serve form, with E (1, 43) = 1.24, p <
.271. The trends of data from pretest to posttest are
presented in Figure 7.

No improvement was identified in ball placement scores

among the three groups. Only the stand-up model group

90
Table 6
Ball Placement Scores (Percentage of Successful Serve) bv

Treatment Condition

 

 

Pretest Posttest
Treatment Condition n M §Q M §Q
Wheelchair Model 15 32.00 20.42 30.00 15.58
Stand-up Model 15 33.33 23.50 33.33 18.39
No Model Control 15 30.00 17.73 19.33 17.51

 

Note. The values represent mean percentages of successfully

served ball out of 10 trials per each block.

91

( 96 Wheelchair Model 0
Stand-up Model E]

 

 

 

35 No Model I;
E: {:1
o—

30

25

20

 

Pretest Posttest

Figure 7. Treatment condition by trials interaction for ball

placement scores (percentage of successful serve).

92

sustained the same group mean score from pretest to the
postest for ball placement. The other two groups
(wheelchair model group and no model group) showed
deteriorated group mean scores on the posttest for ball
placement. The effect size (ES) on the posttest between
the wheelchair model and no model groups was large (ES =
0.61). This effect size indicated that the experimental
group (wheelchair model group) showed less deteriorated
scores for successful serves on the posttest than the
control group (no model group). Similarly, the effect
size (ES) on the posttest between the stand-up model and no
model groups was large, with ES = 0.80.
Intercorrelations Among Three Dependent Variables

Table 7 shows the results of the intercorrelation test
for three dependent variables: (a) form scores; (b) ball
velocities; and (c) ball placement scores. The
correlations ranged from -.30 to .30 among three dependent
variables. There was a significant relationship between
form scores and ball velocities, with r = .30, p < .05.
The better scores the subjects earned from form evaluation,
the higher ball velocities the subjects achieved. There
was a significant relationship between ball velocities and
ball placement scores, with g = -.30, p < .05. The
negative correlation coefficient meant that the higher ball

velocities the subjects showed, the lower percentages of

93
Table 7

Intercorrelations among Three Dependent Variables

 

 

Variables 1 2 3
1. Form Scores -— .30' -.14
2. Ball Velocities -- -- -.30'

3. Ball Placement -- __ __

 

' p < .05

94
successful serves the subjects earned. No significant
relationship was found between form scores and ball
placement scores, with g = —.14, p < .37.
Discussion

The primary purpose of Study 1 was to determine the
effect of model type (wheelchair model versus stand-up
model) on the acquisition of the wheelchair tennis serve.
The results of Study 1 extended previous modeling research
showing that a similar model was more effective than a
dissimilar model on the acquisition of skill in a motor
performance task (George, Feltz, & Chase, 1992; Gould &
Weiss, 1981; McCullagh, 1987). The first hypothesis was
supported by the findings from Study 1. Thus, the similar
model (wheelchair model) was more effective on the
acquisition of the wheelchair tennis serve form than the
dissimilar (stand-up model) and no model. Subjects
receiving demonstrations by a wheelchair model showed
greater improvement in the form of the wheelchair tennis
serve compared to subjects viewing the stand-up model and no
model. Therefore, acquisition of good form in the
wheelchair tennis serve was facilitated by model similarity.

Perhaps the similar demonstration by a wheelchair model
provided more visual stimulation to facilitate cognition of
the serve performance than the dissimilar demonstration by a
stand-up model or no demonstration. Aspects of form are

difficult to convey verbally. Visual information may be

95
necessary to describe this aspect of movement to players.
Because the subjects who were beginning tennis players had
no prior information about the form of wheelchair tennis
serve, perhaps the subjects who received the demonstrations
by a stand-up model had to use those demonstrations to help
conceptualize the wheelchair tennis serve. Also, the
subjects who received no demonstration had to imagine how
they would perform the wheelchair tennis serve by listening
to verbal instruction only. But, the subjects in
wheelchair model group had direct visual instruction by
demonstration treatment that might help them perform the
correct steps of form checklist.

The second hypothesis that able-bodied students
receiving demonstrations by a similar model would show the
greatest improvement in the wheelchair tennis skill as
tested by ball velocity compared to able-bodied students who
viewed the dissimilar or no model was not supported.
Inspection of the ball velocity data indicated that all
three groups improved their ball velocities from pretest to
posttest, but there were no differences between any of
groups as measured by ball velocity on the posttest. The
improvement in ball velocity may due to serve practice
instead of treatment effect. This result indicated that
ball velocity was not facilitated by modeling effects.

This finding from testing the second hypothesis did not

replicate those found by Gould and Weiss (1981). In their

96
study, the group receiving demonstrations by a similar model
(a model of same gender and similar athletic ability) showed
better performance on a muscular leg endurance task than the
group viewed a dissimilar model. Although the experiment
by Gould and Weiss (1981) had used a male and a female model
to produce the similar and dissimilar manipulations, in
Study 1, the investigator had used the body positions of the
model (wheelchair model versus stand-up model) to manipulate
the similarity.

The effect size between two groups (wheelchair model
and no model groups) was more negative (ES = -0.49) on the
posttest tested by ball velocity than the effect size
between two groups (stand-up model and no model groups, ES =
-0.l6). These negative effect sizes indicated that the
experimental groups (the wheelchair model and stand-up model
groups) showed less improvement than the control group (no
model group) tested by ball velocity. This finding
suggests, perhaps, that subjects who viewed demonstrations
were using the model's performance as a goal. Thus, their
ball velocities for the wheelchair tennis serve could be
influenced. But, the subjects not receiving
demonstrations may have cared more about ball velocity than
form.

The third hypothesis that able-bodied students
receiving demonstrations by a similar model would show the

greatest improvement in the wheelchair tennis skill tested

97

by ball placement compared to able-bodied student viewed the
dissimilar or no model was not supported. Thus, the
investigator could not find any significant effect of model
similarity on the acquisition of the wheelchair tennis serve
skill tested by the ball placement. Similarly, the
previous experiment by McCullagh (1986) failed to find
modeling effect on the physical performance outcome scores.

Even though a significant treatment effect was not
revealed for ball placement, the results can be discussed
with reference to the effect sizes between the experimental
groups and the control group. The wheelchair model and no
model groups showed decreased scores for ball placement from
pretest to posttest (Figure 7). However, the experimental
groups (the wheelchair model and stand-up model groups)
showed less decrease for the percentage of successful serves
than the control group. The control group (no model
group) showed the most deteriorated scores for ball
placement on the posttest compared to the ball placement
scores of the wheelchair model group and the stand-up model
group.

According to Bandura (1969), the motivational process
is important in observational learning. Bandura (1986)
emphasized the distinction between skill acquisition and
performance due to a positive incentive. Motivation is
related to inner drives or intentions that cause a person to

behave in a certain way. Motivation can be defined as one

98
of the causes that affect maintenance of behavior (Magill,
1989). In Study 1, wheelchair model and stand-up model
could have influenced motivational processes so that a
positive incentive helped subjects maintain the ball
placement skill.

According to the results from intercorrelations among
three dependent variables, there was a positive relationship
between form and ball velocity. This result indicated
that the subjects who acquired high form scores tended to
show faster ball velocities compared to the subjects who
earned low form scores. Perhaps good serve form may
result in fast ball velocity. Contrasting to such a
positive relationship between form and ball velocity, the
relationship between ball velocity and ball placement was
negative. The higher the ball velocity the subject
showed, the lower the ball placement scores. The subjects
in the no model group tended to serve with higher ball
velocity compared to the subjects in experimental groups.
However, the subjects in the no model group showed the most
deteriorated ball placement scores from pretest to posttest
compared to the subjects who viewed model demonstrations.
These results indicated that a successful serve was
inhibited by fast ball velocity for the beginning wheelchair
tennis players.

It should be noted that the wheelchair tennis serve is

not a simple motor task. A 30-minute training period

99
might be too short to compare the difference of ball
placement skill between the pretest and post test for each
group. It seemed that the time period for the wheelchair
tennis serve instruction was not sufficient to expect an
improvement for ball placement. Also, more repeated
measures for ball placement rather than only a pretest and
posttest may help to detect the gradual change in the ball
placement skill.

An interesting finding in Study 1 was the change in
form scores by subjects who were given demonstrations of the
wheelchair tennis serve. Before seeing demonstrations,
the subjects were not displaying the desired form of the
wheelchair tennis serve. However, upon viewing
demonstrations of the wheelchair tennis serve by a
wheelchair model, they changed their form to become more
like the videotaped demonstration, and improved their form
scores significantly. But the wheelchair model group did
not show any differential improvement in the wheelchair
tennis serve skills tested by ball velocity and ball
‘placement compared to the stand-up and no model group.
fPherefore, form was more sensitive to the effectiveness of
rmodel similarity than ball velocity and ball placement.

The previous experiment by McCullagh (1986) found no
attentional effect dependent on model characteristics when
atteentional differences were inferred from physical

performance outcome scores on the Bachman ladder.

100
However, it may be that outcome scores are not as sensitive
to modeling manipulations as form or strategy components of
the task. Using the same task, Feltz (1982) measured five
form components as well as outcome scores and found that
form was more sensitive to modeling effects than typically
used performance outcome scores.

Qualitative aspects of movement are more difficult to
convey verbally and that visual information would be
necessary to enhance this aspect of movement. Therefore,
the present experiment extended previous research findings
by assessing both qualitative and quantitative aspects of
movement. In a previous study, both qualitative and
quantitative measures were evaluated test by McCullagh,
Stiehl, and Weiss (1990). Their task was a five-part
dance skill sequence.

The measurement in this study could be classified by
the quantitative measure and qualitative measure in the
wheelchair tennis serve. The quantitative measures in
Study 1 were the measurements of ball placement and ball
velocity. The qualitative measure in Study 1 was the form
checklist for the wheelchair tennis serve. The
measurement of serve form was conducted in this study
because Feltz (1982) and McCullagh (1987) found form to be
more sensitive to modeling effects than typically used

performance outcome scores.

101

Although several studies have shown model similarity to
be an important influential factor in motor performance, no
study has addressed wheelchair tennis. The results of
Study 1 suggest that model similarity influenced the
acquisition of serve form of the wheelchair tennis.
However, further considerations seem necessary because the
wheelchair tennis serve is not a simple motor skill.
Therefore, another strategy might include a measure of
effects of modeling for the wheelchair users with
disabilities.

In addition to the type of model, the timing of
demonstrations and the temporal spacing of demonstrations
may be varied generated when teaching the wheelchair tennis
serve. Different modeling strategies can have different
influences on how well the wheelchair tennis serve skill is
acquired by wheelchair users. Therefore, freqeucy and
timing of demonstrations can be considered as influential
factors in teaching the wheelchair tennis serve for
wheelchair users. In Study 2, effects of modeling for the
wheelchair users with disabilities were examined through a
series of learning trials for the wheelchair tennis serve

skills.

CHAPTER IV

STUDY 2

Mendthods
gesearch Design

Independent Variables

The purpose of Study 2 was to determine whether
performance in the wheelchair tennis serve was influenced by
the frequency of demonstrations and timing of
demonstrations. Subjects completed 30 blocks of 10 trials
each. The independent variables consisted of different
frequencies of demonstrations, as well as variation in the
timing of when demonstrations were introduced across the 30
blocks of trials. In condition 1, a total of 27
demonstration sessions were provided in the 4th through 30th
test block. In condition 2, a total of 20 demonstration
sessions were provided in the 11th through 30th test block.
In condition 3, a total of 13 demonstration sessions were
provided in the 18th through 30th test block. In
condition 4, a total of 6 demonstration sessions were

provided in the 25th through 30th test block.

102

103

Dependent Variables

The dependent variables for Study 2 were identical to
those for Study 1 (see pages 58-59).
Experimental Design

The design was a multiple baseline design across
subjects (Figure 8). Each subject completed 30 test
blocks consisting of 10 serve trials each, for a total of
300 serve trials, with each trial consisting of one tennis
serve. The 30 test blocks consisted of a different number
of baseline and intervention sessions for each of the four
subjects. In all cases, intervention sessions involved
the use of videotaped demonstrations of the wheelchair
tennis serve (wheelchair model).

Subject #1

1. Verbal instruction and feedback without
demonstration during the first 3 blocks (10 serves
per block) of the wheelchair tennis serve test
(baseline).

2. Demonstrations with verbal instruction and feedback
preceding every subsequent test block
(intervention in the 4th through 30th test block).

Subject #2

1. Verbal instruction and feedback without
demonstration during the first 10 blocks (10
serves per block) of the wheelchair tennis serve

test (baseline).

104

Subject Test blocks
1 5 10 15 20 25 30

 

Sl BBIIIIIIIIIIIIIIIIIIIIIIIIIII

$2 BBBBBBBBBIIIIIIIIIIIIIIIIIIII

S3 BBBBBBBBBBBBBBBBIIIIIIIIIIIII

U! W CU U

S4 BBBBBBBBBBBBBBBBBBBBBBBIIIIII

 

 

Baseline: verbal instruction and feedback only.
Intervention: verbal instruction, feedback,

and videotaped demonstrations by a wheelchair
model prior to each test block of 10 serve

Note 0

H U!
I

trials. One demonstration session consisted
of 6 demonstrations of the wheelchair tennis
serve.

Figure 8. A diagram of experimental design for Study 2

105

2. Demonstrations with verbal instruction and feedback
preceding every subsequent test block
(intervention in the 11th through 30th test
block).

Subject #3

1. Verbal instruction and feedback without
demonstration during the first 17 blocks (10
serves per block) of the wheelchair tennis serve
test (baseline).

2. Demonstrations with verbal instruction and feedback
preceding every subsequent test block
(intervention in the 18th through 30th test
block).

Subject #4

1. Verbal instruction and feedback without
demonstration during the first 24 blocks (10
serves per block) of the wheelchair tennis serve
test (baseline).

2. Demonstrations with verbal instruction and feedback
preceding every subsequent test block
(intervention in the 25th through 30th test
block).

Each subject completed 30 blocks of 10 trials per block

for a total of 300 serves. Verbal instruction and
demonstrations were provided prior to every block during the

intervention condition. Verbal feedback was provided

106
after every block. The delivery of verbal instruction and
feedback was identical to the methods in Study 1 (see page
73-75).

Rationale for Experimental Design

 

The multiple baseline design across subjects was well
suited for Study 2 for two reasons. First, a small sample
size was required to investigate the intervention effect on
acquisition of the wheelchair tennis serve skills during a
series of learning trials. Second, the investigator was
interested in identifying effects of the frequency and
introduction of demonstrations. The different frequency
and introduction of demonstrations were manipulated across
four subjects by the baseline and intervention conditions.

Testing was a threat to internal validity for Study 2.

Because Study 2 required all subjects to respond to the
same test repeatedly, dependent measures (the scores of
form, ball velocity, and ball placement) were exposed to the
testing threat to internal validity. Also, better
experimental control in Study 2 was achieved when an
acceptable baseline trend was maintained until an
intervention was introduced during a series of learning
trials for the the wheelchair tennis serve. Subject
selection was not a problem since this study focused on a
single individual. Maturation sometimes is a problem in a

single research design. This threat to internal validity

107
was controlled by the short time period for teaching the
wheelchair tennis serve skill in Study 2.
Subjects

Subject Selection Criteria

Wheelchair users who had no prior tennis experience
were needed for Study 2. However, the ability to learn
wheelchair tennis was required for the subjects in this
study, including the ability to carry and swing a tennis
racket. Test 1 from the Strohkendl system (Sherrill,
1993) was used to determine whether subjects had sufficient
body control to learn the wheelchair tennis serve. Test 1
was designed to assess sitting ability and rotation of the
trunk. To pass Test 1, the examinee was required to
bounce and catch a basketball with both hands at the same
time while changing to the opposite side of the chair after
each try. Also, for passing performance, the examinee was
required to rotate his/her trunk as far as possible to each
side without losing balance or leaning back in the chair.
All subjects were required to pass Test 1 of Strohkendl
system to be a subject in this study because of required
function to play wheelchair tennis.
Identification of Potential Subjects

The subjects were wheelchair users who lived in the
mid-Michigan area. Names, ages, genders, and phone
numbers of wheelchair users were obtained from the Offices

that serve students with disabilities at Michigan State

108
University and Lansing Community College. Individuals who
had participated in the wheelchair tennis program coached by
Mr. Stan Drobac were contacted by the investigator to
request help in nominating potential subjects. The
investigator also contacted a wheelchair basketball team in
Ann Arbor. Basketball players who had no experience in
tennis and who were interested in learning to play
wheelchair tennis were eligible to participate as subjects
in this study.
Subject Selection Procedure

The investigator contacted potential subjects by phone.
Outgoing information consisted of introducing the
investigator, explaining his present status as a doctoral
student, and describing the need for wheelchair users as
subjects for a doctoral dissertation. Data collection
included name, gender, age, address, and phone number.

The investigator arranged an appointment with
volunteers to discuss informed consent procedures, and to
administer the Strohkendl test. The subjects were
informed that they should wear comfortable shirts to be
tested. The meeting took place in the IM West Sport Turf
Arena at Michigan State University. If the subjects wanted
the investigator to visit their homes, the investigator
visited them with preparation of informed consent and the

Strohkendl test.

109

A written consent form was distributed to the
subjects and signed at the appointment. The consent form
and the approved application for a project involving human
subjects are included in Appendix A. The Strohkendl test
was administered after a brief introduction about this
study.

The final selection of the subjects was conducted by
the investigator. The total number of potential subjects
was six, including four undergraduate students attending
Michigan State University and two residents in the Ann Arbor
area who were members of the Ann Arbor wheelchair basketball
team. The four actual subjects were selected so as to
insure a narrow age range, equal distribution of genders,
and convenience of transportation to the indoor tennis
court. The remaining two wheelchair users were available
as substutudes in the event of subject attrition.

Subject Characteristics

The number of subjects were four. All subjects were
wheelchair users who were beginning to learn wheelchair
tennis. Subjects had no prior experience in the
wheelchair tennis serve. All wheelchair users had a
significant permanent musculo-skeletal disability such as
spinal cord injury, polio, amputation, etc.

Although all subjects showed the ability to play
wheelchair tennis, additional information about upper body

functions were collected from each subject. This

110
description was used to help explain subjects' performances
in the wheelchair tennis serve. A sample subject
information sheet can be seen in Appendix C. The
information included type of disability, age at onset of

disability, comments about upper body condition, and sport

 

experience.

Subject #1. A male undergraduate student aged 20
years old was selected. The type of disability was C-5
and C-6 paralysis with incomplete quadriplegia. Age at

onset of disability was 16 years old due to an accident.
The subject's abdominal and lower back muscles were weak
because of partial paralysis. The triceps were partially
paralyzed and weak. The forearms, especially wrist
flexors, were also weak, which affected the lack of strength
in the subject’s grip. Subject #1 had prior sport
experiences in basketball, track, and weight-lifting.

Subject #2. A female undergraduate student aged 22
years old was selected. The type of disability was T-12
paraplegia with incomplete quadriplegia. Age at onset of
disability was 19 years old due to an accident. Subject
#2 had no special weakness in strength and mobility of the
upper body. Prior Sport experiences included basketball,
soccer, and swimming.

Subject #3. A male undergraduate student aged 20
years old was selected. The type of disability was

paraplegia. Age at onset of disability was 18 years old

111
due to an accident. Subject #3 had weak muscles around
waist, as well as an inability to flex the upper body 45
degrees forward. Prior sport experiences included
volleyball and weight lifting.

Subject # . A female undergraduate student aged 21

years old was selected. The type of disability was an
amputation above the right knee. Age at onset of
disability was 20 years old due to an accident. Subject

#4 had no special weakness in strength and mobility of the
upper body. Prior sport experiences included softball,
volleyball, basketball, track and field (shot-put and
discus), and swimming. This subject was a member of
volleyball and swimming teams at her high school before her
accident.
Assignment of Subjects to Groups

The subjects were randomly assigned to one of the four
intervention conditions. The random assignment was decided
using a random number generator program.

Igstrumentation

The instrumentation for Study 2 was identical to that
of Study 1 (see pages 65-67). All data-collection and
intervention sessions were conducted using the tennis courts
at the Intramural West Sports building on the Michigan State

University campus.

112
Data-Collection Procedures

Warm-up Session

Each subject did a warm-up practice at the beginning of
each training day. The warm-up period consisted of 5
minutes in which each subject executed 10 tennis serve
swings and ball tosses. During the warm-up period, the
investigator explained how the serve would be performed
(verbal instruction). The verbal instruction was
identical to that of Study 1 (see pages 73-76).
Test Blocks

Each subject did 10 blocks of the wheelchair tennis
serve test in a day. Each block consisted of 10 tennis
serves, for a total of 100 serves in each day. A total of
300 serves were performed across the three-day intervention
period. By inquiring about the subject's fatigue, the

investigator ensured that the subject was not tired during

each test block. Verbal feedback was provided after each
block. In the baseline condition, verbal instruction was
provided to each subject prior to each block. In the

intervention condition, verbal instruction and feedback
followed each block, and the videotaped demonstration
preceded each new block of 10 serve trials. Data-
collection procedures were the same as those of Study 1 (see

pages 69-72).

113
Intervention

The time period for the intervention was l-week, with 2
hours a day and 3 days a week. The practice time, a total
of 6 hours, was sufficient to determine the effects of
modeling. In the curriculum of a beginning tennis class at
Michigan State University, 4 hours of instruction are
provided by most tennis instructors, who were using Brown's
(1989) textbook for tennis serve.
gastruction Procedures

Instruction procedures consisted of verbal directions,
verbal feedback, and videotaped demonstrations. The
administration of the instructional methods is presented in
the experimental design for Study 2 (see pages 103-106).
The videotaped demonstrations used in Study 2 was identical
to the videotaped demonstrations of the wheelchair model
used in Study 1 (see pages 76—78).

Statistical Analvsss

This study was designed to determine the effects of
variations in the frequency and timing of demonstrations on
the acquisition of wheelchair tennis serve skill. In Study
2, visual analysis of graphic data was used to determine the
effects of the intervention (wheelchair model
demonstration). The visual analysis strategy had several
advantages for Study 2. First, the visual analysis
approach, as a compact and detailed data-reporting format,

permitted the investigator to analyze data trends both

114
within and across the four subjects in Study 2. Second,
the data for each subject could be presented point-by-point
for serve form, ball velocity, and ball placement. Third,
it was easy to discriminate data positions and data paths
across a series of learning trials.

To determine the influence of an intervention on the
serve form, ball velocity, and ball placement, the magnitude
of change in the dependent variables was assessed when
moving from one condition (baseline condition) to another
(experimental condition). The amount of change indicated
the immediate strength or impact the intervention had on the
subject's performance of the wheelchair tennis serve.

When a large change in level occurred after the introduction
of an intervention, the level change was considered abrupt,
which was indicative of a powerful or effective
intervention.

The trend or lepe of a data series is as important as
the level of performance. In combination, a careful
analysis of level and lepe permits a reliable determination
of experimental effect. SIOpe referred to the amount of
change in dependent variable path across 30 blocks in Study
2. A line of best fit was calculated using regression
equation. The linear regression equation is as follow:

Y = a + bx

Where

I-<
II

dependent variable

115
x = number of block

a intercept

b

lepe

The split-middle method (White & Haring, 1980) was used
to estimate the patterns of the scores for form, ball
velocity, and ball placement. Additionally, change in
variabilities of the form score and ball velocity were
identified by standard deviation in each test block in order
to determine the consistency of the scores of form and ball
velocity. Ball placement was simply described by the
percentage of successful serves in each test block without
standard deviation. This method was based on a summary of
data patterns across two conditions which was presented by
Tawney and Gast (1984) for common data pattern between
conditions (baseline and intervention). A diagram for
statistical analyses can be seen in Figure 9.

Results and Discussion for Study 2
Results

The results of Study 2 have been organized according to
the hypothesis tested. A visual analysis of the data
supported the first hypothesis that timing and frequency of
demonstrations would influence the acquisition of correct
form in the wheelchair tennis serve. The visual
analysisof data did not support the second hypothesis that
timing and frequency of demonstrations would influence ball

velocity in a series of learning trials for the wheelchair

116

 

 

 

 

 

 

 

 

Hypothesis 1 Hypothesis 2 Hypothesis 3
Summary Sl>SZ>SB>S4 Sl>SZ>S3>S4> Sl>SZ>S3>S4
of in in in
Hypo- Serve form Ball velocity Ball
thesis placement
Test Visual analysissof graphic data
for a. change of level
main b. change of slepe
effect c. variability

 

81: Subject
82: Subject
S3: Subject
S4: Subject

Sl>SZ>S3>S4: A wheelchair user receiving a higher frequency
of demonstrations and an earlier introduction
of demonstrations during a series of learning
trials of the wheelchair tennis serve will show

1
2
3
4

greater improvement in the wheelchair tennis
serve skill as tested by serve form, ball
velocity, and ball placement compared to the
wheelchair users receiving a lower frequency
and a later introduction of demonstrations.

Figure 9. A diagram of statistical analyses for Study 2

 

117

tennis serve. Similarly, visual analysis of data did not
support the third hypothesis that timing and frequency of
demonstrations would influence ball placement scores in a
series of learning trials for the wheelchair tennis serve.
Hypothesis 1

The form scores with means and standard deviations are
presented in Table 8. The visual data for serve form
forthe baseline and intervention conditions are presented in
Figure 10. The simple data patterns for serve form scores
are illustrated in Figure 11. Standard deviations are
illustrated by graphs in Figure 12, which was used to
determine the variability of form scores for each test
block. The visual analysis of data supported the first
hypothesis by its abrupt change of level for the serve form
scores for three of the four subjects after the introduction
of demonstrations at Block 4 for Subject #1, Block 11 for
Subject #2, Block 18 for Subject #3, and Block 25 for
Subject #4. Subject #1 showed 18.7% increase from the
last block of baseline to the first block of intervention.
Subject #2 showed 43.7% increase from the last block of
baseline to the first block of intervention. Subject #3
showed 6.3% decrease from the last block of baseline to the
first block of intervention. Subject #4 showed 31.3%
increase from the last block of baseline to the first block

of intervention.

118
Table 8

Serve Form Scores (Percentage of Successful Steps)

 

Block Subject #1 Subject #2 Subject #3 Subject #4

 

 

 

 

 

!(%) §2(%) M(%) §Q(%) fl(%) §2(%) !(%) §Q(%)
1 B 25.0 5.1 B 18.8 4.2 B 37.5 9.3 B 25.0 5.1
2 B 25.0 3.0 B 18.8 5.1 B 43.8 5.1 B 25.0 3.0
3 B 31.3 4.2 B 25.0 4.2 B 37.5 4.2 B 31.3 4 2
4 * I 50.0 5.1 B 25.0 4.2 B 43.8 5.1 B 37.5 4.2
5 I 56.3 4.2 B 25.0 5.1 B 43.8 5.1 B 50.0 5.1
6 I 62.5 5.1 B 25.0 5.1 B 43.8 3.0 B 56.3 3.0
7 I 50.0 9.3 B 25.0 4.2 B 50.0 3 0 B 68.8 3.0
8 I 50.0 4.2 B 31.3 3.0 B 56.3 4.2 B 75.0 5.1
9 I 50.0 4.2 B 31.3 2.0 B 56.3 3.0 B 75.0 4.2
10 I 50.0 9.3 B 31.3 5.1 B 62.5 4.2 B 75.0 3.0
11 I 50.0 5.1 *I 75.0 4.0 B 56.3 3.0 B 87.5 2.0
12 I 50.0 4.2 I 81.3 3.0 B 50.0 2.0 B 81.3 4.2
13 I 50.0 4.2 I 87.5 4.0 B 50.0 2.0 B 75.0 4.2
14 I 43.8 5.1 I 87.5 2.0 B 56.3 0.0 B 62.5 3.0
15 I 43.8 3.0 I 87.5 2.0 B 56.3 0.0 B 68.8 5.1
16 I 43.8 2.0 I 93.8 3.0 B 56.3 0.0 B 68.8 5.1
17 I 43.8 0.0 I 93.8 2.0 B 68.8 2.0 B 75.0 9.3
18 I 43.8 3.0 I 93.8 2.0 *1 62.5 3.0 B 68.8 3.0
19 I 43.8 5.1 I 93.8 4.2 I 68.8 4.2 B 68.8 5.1
20 I 43.8 2.0 I 93.8 0.0 I 56.3 5.1 B 68.8 2.0
21 I 43.8 2.0 I 93.8 2.0 I 75.0 3.0 B 62.5 2.0
22 I 50.0 5.1 I 93.8 2.0 I 68.8 4.2 B 62.5 0.0
23 I 56.3 5.1 I 93.8 0.0 I 81.3 6.1 B 62.5 0.0
24 I 50.0 4.2 I 93.8 0.0 I 81.3 5.1 B 62.5 0.0
25 I 68.8 4.2 I 93.8 2.0 I 93.8 3.0 *I 93.8 4.2
26 I 68.8 0.0 1100.0 0.0 I 93.8 3.0 I 93.8 3.0
27 I 68.8 2.0 1100.0 0.0 I 93.8 0.0 I 93.8 3.0
28 I 68.8 0.0 1100.0 0.0 I 93.8 0.0 1100.0 0.0
29 I 68.8 0.0 1100.0 0.0 I 93.8 0.0 1100.0 0.0
30 I 68.8 0.0 1100.0 0.0 I 93.8 0.0 1100.0 0.0

 

Note. B: Baseline
I: Intervention
*: Start of intervention

119

BASELINE INTERVENTION
[7.)
100

Subiect 1

 

l l J

10 20 30

so - '
. f Subiect 2

‘I
l’ l

10 20 so

 

 

 

 

 

 

100

50 .aharbdhdfiflrfflr“‘fihdfp'_ff‘ E

Subiect 3

1o 2% 20 so

 

 

 

 

 

50

’ Subiect 4
1 2'0 ‘ 50

 

 

 

10
Test Blocks [10 serves per block)

Figure 10. Percentage of serve form scores over 30 blocks of

serve test .

120

 

 

 

 

 

 

 

 

 

 

BASILINE INTCR'IENTION
[Z]
100
50
_ Sabin“
100
50
__,_.——- Suwoet 2
100 ‘Irflflfuflarrun-
.ruhisst 3
Sulfiut 4
10 20 30

 

 

 

Test Blocks [10 serves per block]

Figure 11. Data patterns (level and lepe) for serve form

scores over 30 test blocks.

121

BASELINE INTERVENTION
[Z]
10

 

10 1o 20 so

 

 

 

 

 

 

10

 

 

 

Test Blocks

Figure 12. Standard deviations for serve form scores over 30

test blocks.

122

The lepes in the lines of best fit for the baseline
scores and the intervention scores were evaluated by the
linear regression equation. Subject #1 showed no lepe in
the regression line for the baseline scores, with s =.00.
However, he showed a positive lepe in the line of best fit
for the intervention scores, with s = .60. Subject #2
showed the positive s10pes in the baseline and intervention
scores, with s = 1.40 for the baseline and s = .96 for the
intervention. Subject #3 showed positive lepes, with s =
1.41 for the baseline and s = 3.20 for the intervention.
Subject #4 showed positive slepes, with s = 1.29 for the
baseline and p = 1.59 for the intervention. The amount of
the estimated value of s in the linear equation indicated
the trend of data during the baseline condition and the
intervention condition.

Standard deviations were used to examine the
consistency of form scores in each test block. During the
last three blocks of the form test, high consistencies of
the form scores were shown by all subjects, with §Q = .00.
These results indicated that the subjects showed very
consistent serve forms at the end of the instructional
period. Subject #1 and Subject #2 did not show the
continuous zero standard deviations during the baseline, but
Subject #3 and Subject #4 showed three continuous low
variabilities during the baseline, with sg = .00. These

results indicated that the consistency of serve form

123
performance was seen in the baseline condition when Subject
#3 and Subject #4 received a longer baseline condition than
Subject #1 and Subject #2.

Hypothesis 2

The average ball velocities with means and standard

deviations are presented in Table 9. The visual data for
ball velocities are presented in Figure 13. The simple
data patterns are presented in Figure 14. Standard

deviations for ball velocity in each test block are
illustrated in Figure 15. The visual analysis of data did
not support the second hypothesis because it showed no
abrupt change in the level for ball velocity after an
introduction of demonstrations across the four subjects.

The amounts of change of ball velocity between the last
block of baseline and the first block of intervention are
-2.8 mph for Subject #1, 2.1 mph for Subject #2, -7.0 mph
for Subject #3, and -4.6 mph for Subject #4. The negative
values indicated that subject showed decreased ball velocity
after the introduction of demonstrations. Therefore, the
introduction and frequency of demonstrations did not result
in improved ball velocity for these subjects.

The lepes in the lines of best fit for the baseline
scores as well as the intervention scores were evaluated by
linear regression equations. Subject #1 showed no lepe
in the regression line for the baseline and intervention

scores, with p = .00. Subject #2 showed a negative lepe

124

Table 9

(mph)

J

 

Average Ball Velocities

Subject #3 Subject #4

Subject #2

 

Block Subject #1

M.

M.

M_

M_

433566.].8nU.n/u25113613637w511876685

O .....
311223123345333324432323435463

583692441707457347184233700656

m26611035305000643724244931756
333344444443444343344444344444

BBBBBBBBBBBBBBBBBBBBBBBBIIIIII

 

al.84334449631840926283445027324

364”234..334433333633223332243445

m74129253453887700835594035086

....... O O O O I O O O O O O O O I O O O I
839029001222924169091nw0433243nw
343443444444344443434444444444

BBBBBBBBBBBBBBBBBIIIIIIIIIIIII

 

35.].506065289457482068898742366

BAHZAH5432223444432333233264.3342

316080057239300232883173892569

435010189912664644650404324443
333333322233333333333333333333

BBBBBBBBBBIIIIIIIIIIIIIIIIIIII

313243520848501547661262459874
O O

44axwdn34544444355422143323531124

21686601633rb.150.358375773480535

O OOOOOOOOOOOOOOOOOOOO
587498103289191.918196989882008
222222333322323232322222223332

 

BBBIIIIIIIIIIIIIIIIIIIIIIIIIII
*

01234567890
12345678911111111112

 

Start of intervention

Intervention

*:

 

Note. B: Baseline

BASELINE INTERVENTION

125

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(mph?
50 3:
25 ,n_.”_fhaF"fL_‘5—h"F4—‘JHurJ—‘\’f‘_J_-af*"h*ku
5' Subiect1
., 10 20 30
so ‘ 3E
25
if Subicct?
1°35 _* 20 30
50 W ...... ‘:E
inhua-_J’h'_“"‘hh
Subicct3
10 i 20 30
50 E
-aflPdfidfllflfl“‘Hhfl‘dh“’\iflF‘#~h—Jh.'hfquF‘F‘
25
Subiectd
1’ J 4
Test Blocks [10 servcsopcr block] 20 30

Figure 13. Average ball velocities (mph) over 30 blocks of

serve test .

126

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BASELINE lN‘l’tRVIN'flON
(mph: Sukiyaki
$0
25 ,._
50 swam
25 _
50 4 Surfing“)
25
Suuocu
50
4 —-—-‘
25
10 20 30

 

Test Blocks [10 serves per block)

Figure 14. Data patterns (level and sloPe) for ball

velocities over 30 test blocks.

127

BASEUNE NTERVENTION
[mph]

10
10 i
Jlllullu. T

10: 20 30
10 ‘

 

10 20 30

 

 

 

 

 

 

 

 

1o.

 

 

Test Blocks 10 30 30

Figure 1;. Standard deviations for ball velocities over 30

test blocks.

128
for the baseline data and no $10pe for the intervention
data, with b = -.63 for the baseline and b = .00 for the
intervention data. Subject #3 showed the positive lepes,
with b = .24 for the baseline and b = .28 for the
intervention data. Subject #4 showed the positive slopes,
with b = .27 for the baseline and b = 1.39 for the
intervention data. The negative lepe indicated that the
subject showed decreased ball velocities across the trial
blocks. The positive 310pe indicated that the subject
showed the increased ball velocities.

Standard deviations were used to examine the
consistency of ball velocities in each test block. None
of the subjects showed much consistency for ball velocity
within a test block. Only Subject #2 showed three
continuous low standard deviations at the last three blocks
of baseline, with §Q = 2.6, 2.5, and 2.2. These results
indicated that the consistency of learned performance for
ball velocity was hardly seen during the instructional
period.

Hypothesis 3

The ball placement scores with means were presented in
Table 10. The visual data for ball placement are
presented in Figure 16. The simple data patterns for ball

placement scores are presented in Figure 17. The visual

129
Table 10

Ball Placement Scores (Percentage of Successful Serve)

 

 

 

Block Subject #1 Subject #2 Subject #3 Subject #4
1 B 10 B 60 B 10 B 60
2 B O B 30 B 20 B 50
3 B O B 50 B 30 B 70
4 *I 0 B 60 B 60 B 70
5 I 0 B 20 B 20 B 70
6 I O B 60 B 50 B 40
7 I O B 50 B 40 B 60
8 I 20 B 70 B 40 B 60
9 I O B 60 B 30 B 30
10 I 30 B 30 B 50 B 20
11 I 20 *I 50 B 30 B 90
12 I 30 I 60 B 30 B 50
13 I 30 I 50 B 30 B 50
14 I 50 I 20 B 50 B 60
15 I O I 10 B 20 B 40
16 I O I 20 B 20 B 50
17 I 40 I 30 B 70 B 90
18 I 30 I 30 *I 10 B 80
19 I 30 I 40 I 30 B 50
20 I 20 I 40 I 60 B 30
21 I 40 I 20 I 50 B 70
22 I 20 I 30 I 50 B 70
23 I 30 I 50 I 10 B 20
24 I 10 I 70 I 30 B 70
25 I 70 I 50 I 40 *I 60
26 I 40 I 40 I 40 I 40
27 I 40 I 70 I SO I 40
28 I 20 I 60 I 40 I 20
29 I 20 I 50 I 10 I 50
30 I 20 I 60 I 50 I 60

 

Note. Each value represent single score without standard
deviation.
B: Baseline
I: Intervention
*: Start of intervention

 

 

130

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BASELINE INTERVENTION
(Z)
100
50
100 10 20 30
50 W
10" 20 30
100 j
10 E 20 30
100 ’
1'0 2'0 ' 36
Test Blocks [10 serves per block]
Figure 16. Percentage of ball placement scores over 30

blocks of serve test.

131

 

 

 

 

 

 

 

 

BASIN"! INTIR'IINTION
100 [z] SUEDE“
100 Satin: 2
50 \M W
100 Inhint 3
50
Sun": 4
100
so W V
20 30

 

10
Test Blocks [10 serves per block]

Figure 17. Data patterns (level and slope) for ball

placement scores over 30 test blocks.

132
analysis of data did not support the third hypothesis
because it did not show any abrupt change in the level on
the scores for ball placement after the introduction of
demonstrations across the four subjects. The changes of
level for ball placement scores were affected by the high
variability of the data. The amounts of change for ball
placement scores between the last block of baseline and the
first block of intervention are 0% for Subject #1, 20% for
Subject #2, -60% for Subject #3, and -10% for Subject #4.
The negative values indicated that subject showed a
decreased percentage of successful serves after the
introduction of demonstrations. Therefore, variations in
the introduction and frequency of demonstrations did not
affect scores for successful ball placement as hypothesized.
The slopes in the lines of best fit for the baseline as well
as the intervention data were evaluated by linear regression
equations. Subject #1 showed zero slope for the baseline
data, with b = .00. However he showed a positive slope
for the intervention data, with b = 1.08. Subject #2
showed no slope for the baseline data. However, she

showed a positive 310pe for the intervention data, with b =

1.32. Subject #3 showed zero lepes for the baseline and
intervention data. Subject #4 showed zero lepes for the
baseline and intervention data. Results indicated that

there was no intervention effect on ball placement because

stability of the data was not acceptable to test the data

133
patterns by visual analysis. Although Subject #1 and
Subject #2 showed positive s10pes for the intervention data,
the fluctuation of data ranged over 15% of the stability
criterion (Tawney & Gast, 1984). Therefore, the
investigator could not find any treatment effect on the ball
placement scores for the four subjects in Study 2.
Discussion

The purpose of Study 2 was to further understand
effects of demonstrations by a similar model in a series of
learning trials for the wheelchair tennis serve skill.

The results of Study 1 indicated that a similar model
(wheelchair model) was identified as a better model to
improve serve form than the dissimilar model (stand-up
model). Therefore, the videotaped model who used a
wheelchair was shown for wheelchair users with disabilities
in Study 2.

The first hypothesis which related to the form of the
wheelchair tennis serve was supported by visual analysis.
The subjects showed abrupt improvement in the level of form
scores after an introduction of demonstrations, indicating
that demonstrations were effective in helping to improve the
form scores for the wheelchair tennis serve.

Subject #2 showed greater improvement in the wheelchair
tennis serve skill tested by serve form compared to Subject
#3 and Subject #4. This result clarified the timing

effect of demonstrations; namely, an earlier introduction of

134
demonstrations was more effective on form than a later
introduction of demonstrations. Then, the reason why
Subject #1 showed less improvement in the form scores
compared to Subject #2 should be noted. This result might
be due to the characteristics of Subject #1 (see pages 109-
111). Because Subject #1 had a limited on the range of
arm motion, he showed limited percentage on achieving

correct steps in form checklist such as ball toss and ball

contact. He could not perform full extension of his arm
for ball toss. The arm and racket were not fully extended
when hitting the ball. Thus, the comparison of Subject #1

to other subjects by data pattern should be considered under
the influence of limited body motion. Therefore, a more
homogeneous sample is suggested for the future studies in
order to control such variables (Kirk, 1982).

Results of Study 2 were based upon the findings of
Study 1 that the wheelchair model intervention facilitated
the acquisition of correct form on the wheelchair tennis
serve. This result indicated that subjects were sensitive
to the model's form, instead of ball velocity and ball
placement during demonstrations. The reason subjects were
sensitive to the serve form was explained by Brown (1989).
He noted that all beginning tennis players were interested
in qualitative technique first. Another plausible
explanation for these results was due to the encouragement

for serve form provided by a verbal emphasis of form during

135
the instruction period. Verbal direction was consisted of
the sequence of the correct form, and demonstration was
characterized by form also.

The data of Subject #2, #3, and #4 showed an increase
of the scores for form during the baseline, which was
determined by the slope in regression equation during the
baseline data. This result indicated that subjects could
improve their form with verbal instruction. However, the
influence of modeling was more prominent than verbal
instruction, which was determined by an abrupt change of
level between the baseline and intervention condition across
three of the four subjects. The positive change of lepe
between the baseline and intervention data was found across
three of the four subjects (Subject #1, #3, and #4). In
particular, Subject #3 showed higher lepe than Subject #4
during the intervention condition. These results
indicated that the frequency of demonstrations influenced
serve form when the demonstrations were introduced after
long baseline period.

The consistency of learned performance was examined by
the inspection of the trend for standard deviations in form
scores. All subjects showed zero variabilities during the
last three blocks of the intervention condition, with SQ =
.00. The low standard deviation with high form score
indicated that consistent form was correctly performed in

the wheelchair tennis serve. The consistency of serve

136
form was also found in the baseline with Subject #3 and #4.
However, their levels of form scores during the baseline
were lower than the levels of form scores during the last
three blocks of the intervention condition.

Visual analysis of the trends for ball velocity scores
did not support the second hypothesis. There was no
abrupt change of the scores for ball velocity after an
introduction of demonstrations. And there was no
increasing trend by the Subject #1 and Subject #2 who
received an earlier introduction and a higher frequency of
demonstrations during the intervention condition either.
These results indicated that subjects did not show any
effectiveness of demonstrations on the scores for ball
velocity.

Perhaps the instructional method of this study, which
used verbal feedback to enhance ball velocity was not
sufficient to motivate the subjects to increase ball
velocity. This result was not based on the finding from
Study 1. In Study 1, all subjects showed improvement in
the scores for ball velocity from pretest to posttest.
This controversial result could be explained by the
difference of training period and number of tests between
Study 1 and Study 2. Study 2 was delimited by one week
(two hours per day, three days per week) and 30 blocks of
serve tests. This longer training period and more

additional repetitions of the serve could help the subject

137
to acquire consistent ball velocity. Therefore, no abrupt
change of ball velocity between the baseline and
intervention was determined in Study 2.

The change of standard deviations across 30 blocks of
serve tests was not prominent enough to identify the
consistency of learned performance tested by ball velocity.
Even though consistent ball velocities over 30 test blocks
were shown across four subjects, the variability did not
decrease during the 30 blocks of serve tests. It seemed
that more practice time was needed to achieve low
variability for ball velocity.

The third hypothesis was not supported by visual
analysis of the graphic data for ball placement. The
variability of data was prominent and the fluctuation of
data was high (over 15%) in the score ranges so that the
data were not acceptable to evaluate the change level and
lepe. The great variability indicated that none of the
subjects achieved consistency in scores for ball placement.
This result meant that ball placement was not a simple
outcome but a more complicated outcome. The delimitation
of training period (a total of 6 hours) did not enable the
subjects to develOp consistent behavior for ball placement.

Few modeling studies have assessed modeling effects on
qualitative changes in motor skills such as form or
technique (Feltz, 1982; McCullagh, 1986; McCullagh, Stiehl,

& Weiss, 1990). What really interests researchers and

138
practitioners is the quality of movement such as the
technique of a movement, matching of a fundamental motor
skill, or the overall coordination of body parts in relation
to a skill sequence. The results of Study 2 replicated
the findings from other modeling studies, namely that form
is more sensitive to modeling effect than physical
performance outcome scores.

Attention has been given to the temporal Spacing of the
model (Anderson et al., 1982; Landers, 1975) and to the
number of demonstrations (Feltz, 1982). Anderson et al.
(1982) concluded that temporal spacing of the model (before
or middle of the task) did not affect stabilometer
performance. Feltz (1982) concluded that 12 videotaped
demonstrations were more effective on Bachman ladder
performance and form than 0, 4, or 8 videotaped
demonstrations. Additionally, it was suggested from these
studies that future research should be concerned with the
effectiveness of modeling, the nature of the task, mode of
presentation, and characteristics of subjects. In Study
2, variations in the timing of demonstrations were used.

The results of Study 2 indicated that an earlier
introduction of demonstrations was more effective on the
serve form scores than later introduction of demonstrations.
The results of Study 2 replicated Feltz's (1982) conclusion
that a greater number of demonstrations was effective on the

performance tested by the wheelchair serve form compared to

139
a fewer number of demonstrations.

Similar to the investigation of Anderson et a1. (1982),
Landers (1975) examined temporal spacing of demonstrations
and audience presence in relation to Bachman ladder
performance. Model demonstration entailed the use of
three types of temporal spacing: (a) before performance; (b)
interspaced before and midway through the trials; and (c)
midway only. In contrast to Anderson's results, Landers
found that the best temporal spacing for modeling occurred
when model demonstrations were provided before and
interspaced through learning trials.

In Study 2, the subjects profited more from the
demonstrations with respect to form rather than ball
velocity or placement. This trend replicated the result
in Study 1. McCullagh (1987) and Feltz (1982) emphasized
that form or strategy components were more sensitive to
modeling effects than performance outcome scores. Also,
qualitative aspects of movement such as form are more
difficult to convey verbally, and visual information seems
to help the subjects to understand the aspects of serve form
more than verbal information. The demonstration of the
wheelchair tennis serve could provide more visual effects
for each subject than verbal instruction. Therefore,
subjects could enhance their form after an introduction of

demonstrations.

CHAPTER V

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

Summary
The purpose of Study 1 was to determine the effects of
skill demonstrations by the wheelchair and stand-up models
(type of model) on the acquisition of the wheelchair tennis
serve. Results of Study 1 showed that a wheelchair model
was more effective than a stand-up model or no model as a
method of teaching the wheelchair tennis.

The purpose of Study 2 was to determine the effects of
frequency and timing of demonstrations throughout a series
of learning trials for the wheelchair tennis serve. The
frequency of demonstrations and the timing of the
introduction of demonstrations were the main treatments in
Study 2. A higher frequency and an earlier introduction
of demonstrations of the wheelchair tennis serve were
effective in the acquisition of serve form. The subject
receiving a higher frequency and an earlier introduction of
demonstrations showed greater improvement in the scores for
serve form than the subject receiving a lower frequency and

a later introduction of demonstrations.

140

141
Study 1

The subjects consisted of 45 able-bodied students from
Michigan State University who were beginning tennis players.
The subjects were randomly assigned to one of three
treatment conditions. Two experimental groups (a
wheelchair model condition and a stand—up model condition)
received videotaped demonstrations, and one control group
received no demonstration. Three dependent variables
consisted of a test of serve form, a test of ball velocity,
and a test of ball placement. Pretests were administered
to the subjects prior to the 30-minute treatment period, and
posttests were administered to the subjects after the
treatment period.

Results of the pretests were analyzed by ANOVA to test
the assumption of equality of variance across the
experimental groups. Main effects of treatment and
interaction were determined by means of 3 x 2 (Model Type x
Trials) ANOVA with repeated measures for each dependent
variables. The Newman-Keuls post hoc test was employed
for the follow-up method. Additionally, the effect sizes
were calculated to compare the difference between two means
of the posttests between the experimental groups and the
control group. Discriminant analysis was performed to
determine the main effects in conjunction with the

correlations among three dependent variables.

142

Results of Study 1 indicated that the subjects who
received a videotaped demonstration by a model who used a
wheelchair showed better performance of the wheelchair
tennis serve as tested by serve form compared to the
subjects viewing a stand-up model or no model. Although
no effectiveness of model type was detected in the
performance tested by ball velocity, the subjects improved
their ball velocity from pretest to posttest. However, no
effectiveness of model type and no improvement for ball
placement was detected in Study 1. In conclusion, the
demonstration by a similar model (a wheelchair model) was
determined as an effective model to enhance form of the
wheelchair tennis serve for the beginning tennis players who
used a wheelchair.

Study 2

Study 2 was conducted to determine the effects of
frequency and timing of demonstrations during a series of
learning trials (300 wheelchair tennis serve trials) by
wheelchair users. The serve trials were blocked by 30
sessions in which each block consisted of 10 serve trials.
During the baseline condition, only verbal instruction was
provided to each subject. Both videotaped demonstrations
by a model who used a wheelchair and verbal instruction were
provided during the intervention condition. The subjects
consisted of four wheelchair users (three with spinal cord

injuries and one with a leg amputation) who were

143
undergraduate students at Michigan State University. The
subjects had no prior experience in the wheelchair tennis
serve.

A multiple baseline design across subjects was used in
Study 2. Each subject was exposed to the baseline and
intervention condition. The subjects were randomly
assigned to four different intervention conditions: (a)
videotaped demonstrations before the last 27 blocks of
serves; (b) videotaped demonstrations before the last 20
blocks of serves; (c) videotaped demonstrations before the
last 13 blocks of serves; and (d)videotaped demonstrations
before the last 6 blocks of serves. The test of the
wheelchair tennis serve followed each block of 10 serves.
Three dependent variables consisted of the test of serve
form, test of ball velocity, and test of ball placement.

Results of the 30 blocks of the wheelchair tennis serve
were analyzed by the visual inspection of graphic data.

From the visual analysis, the effect of frequency and timing
of demonstrations revealed that the subject who received a
higher frequency of demonstrations and an earlier
introduction of demonstrations showed greater improvement in
the wheelchair tennis serve skill tested by serve form
compared to the subjects receiving a lower frequency of
demonstrations and a later introduction of demonstrations.

This result extended the previous result in Study 1 that

144
there was modeling effect on acquiring the form of the
wheelchair tennis serve.
Conclusions

Within the limitations of this study, the following
conclusions were reached:

1. A demonstration by a similar model who used a
wheelchair was more effective for enhancing form in the
wheelchair tennis serve performance by wheelchair users than
a demonstration by a stand-up model or the absence of a
demonstration.

2. The type of model was not a determinant of modeling
effects on the test of ball velocity or ball placement in
the wheelchair tennis serve. No effectiveness was found
for ball velocity and ball placement after treatment by a
model type.

3. A wheelchair user receiving a higher frequency and
an earlier timing of demonstrations tended to show greater
improvement in wheelchair tennis serve form than a
wheelchair user receiving a lower frequency and a later
introduction of demonstrations.

4. The frequency and timing of demonstrations were not
influential for improving ball velocity and ball placement.
The subjects showed no abrupt change of level or s10pe
between the baseline condition and the intervention

condition.

145
Recommendations

The following recommendations are offered for further
studies as a result of this investigation:

1. A study similar to Study 1 utilizing a larger sample
size should be replicated to permit more rigorous
statistical analysis. For a given value of the parameter
being tested, the power of the test of hypothesis increases
as the sample size increases.

2. A study similar to Study 1 utilizing a sample of
wheelchair users with disabilities may be conducted over a
longer period of time to investigate the effects of model
similarity on persistence in wheelchair tennis.

Persistence should be an important factor in a successful
achievement of the wheelchair tennis skill. The benefits
of the wheelchair tennis activity should result when
wheelchair users are persistent in participating in learning
trials for the acquisition of the wheelchair tennis serve.

3. A study similar to Study 2 utilizing biomechanical
analysis of serve form should be replicated to permit a more
mechanical description about changes in serve pattern. To
examine relative motion patterns such as form, biomechanical
techniques allow for quantitative evaluation of kinematic
parameters.

4. A study similar to Study 2 using model
demonstrations as baseline and discontinuing at different

points along serve practice should be replicated to

146
determine the effects on the maintenance for the wheelchair
tennis serve skill.

5. A study similar to Study 2 recruiting more
homogenious sample than the subjects in Study 2 should be
replicated to test retentional outcome for the wheelchair
tennis serve.

6. A survey should be completed to ask subjects what
they are most concerned with: (a) form, (b) ball velocity,

or (c) ball placement.

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Sherrill, C. (1981). Adapted physical education and
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Sherrill, C. (1993). Adapted physical activity.
recreation and sport: Crossdisciplinary and lifespan (4th
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SiedentOp, D. (1983). Develolopingsteaching skillsfin
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Smith, S. L. (1979). Comparison of selected kinematic
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153

Tawney, J. W., & Gast, D. L. (1984). Single subject
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Merrill Publishing Company.

Thomas, J. R., & Nelson, J. K. (1985). Introduction to
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APPENDICES

APPENDIX A

HUMAN SUBJECT APPROVAL AND INFORMED CONSENT FORM

154

 

WRITTEN CONSENT FORM FOR STUDY 1

 

To participants in this study:

I am a graduate student at Michigan State University.
The subject of my doctoral dissertation is: "Acquisition of
the wheelchair tennis serve by wheelchair users: type of
model and frequency and timing of demonstrations." I am
presently in the preparation of a pilot study for the
doctoral dissertation. In the pilot study, I am
interested in the effects of model characteristics in the
acquisition of the wheelchair tennis serve by nondisabled
beginning tennis players.

I would like have consent for your participation in
this study which will be conducted by testing your
wheelchair tennis serve skill in one of three different
demonstration conditions. A total of 30 min. will be
provided for demonstrations and practice of the wheelchair
tennis serve. You will be tested to determine the
acquisition of the serve skill while sitting in a
wheelchair. Your form, accuracy, and ball velocity will
be evaluated.

This study will be done under anonymity and
confidentiality, therefore, I will not use your name, names
of people close to you, the name of your school, or your
address and phone number. You will freely consent to
participate and may refuse to participate at any time
without penalty or loss of benefits. In signing this
form, you are also assuring me that you will make no
financial claims for the use of the test results of your
tennis performance in wheelchair tennis serve. You are
also stating that no medical treatment will be required by
you from Michigan State University.

You may contact the investigator regarding any questions or
concerns that may be raised by participating in this study.

I, have read the above statement
and agree to participate as a subject in wheelchair tennis
practice under the conditions stated above.

 

Signature of participant

 

Signature of investigator Date

 

Investigator: Kihong Kim (Phone: 517-355-2805)

155

 

WRITTEN CONSENT FORM FOR STUDY 2

 

To participants in this study:

I am a graduate student at the Michigan State
University. The subject of my doctoral dissertation is:
"Acquisition of the Wheelchair Tennis Serve by Wheelchair
Users: Type of Model and Frequency and Timing of
Demonstrations."

As a part of this study, you are being asked to learn
the wheelchair tennis serve. You will participate in
three two-hour practice sessions within a one-week period of
time. Each day you will perform about 100 tennis serves.
Instruction of the wheelchair tennis serve will be provided
with a demonstration. I am interested in your skill
improvement in the wheelchair tennis serve.

Since the number of subjects in this study is small,
subject's identity cannot be anonymous to the researcher,
but your identity will not be revealed in any report of the
results of this study. Also, I will not use names of
people close to you, the name of your school, or your
address and phone number in any report of the results of
this study.

You will freely consent to participate and may refuse
to participate at any time without penalty or loss of
benefits. Performance scores will be given to you if
requested. You may contact the investigator regarding any
questions or concerns that may be raised by participating in
this study.

 

I have read the above statement and agree to participate as
a subject in wheelchair tennis practice under the conditions
stated above.

 

Name of participant (please print)

 

Signature of participant

Date

 

 

Signature of investigator

Investigator: Kihong Kim (Phone: 517-355—2805)

1565

 

ERHIAJI SIHLJEKIIS IUPPTKNMAI.

 

 

OFFICE OF
RESEARCH
AND
GRADUATE
STUDIES

Imhuuw0mmmmnon
mnummuqum)
Human Sublets
HEBMB)

Michigan Stale University
225 Administration Building
EaSI Lansing. Michigan
MENJO“

517t355~2180
FAX: 51 "432.1 1 71

MICHIGAN STATE

 

 

UNIVERSITY
October 5, 1994
TO: Kihon Kim
1518- Spartan Village.
East Lansing, MI 48 23
RE: IRBI: 94-470
TITLE: ACQUISITION OF THE WHEELCHAIR TENNIS SERVE BY

WHEELCHAIR USERS: TYPE OF MODEL AND FREQUENCY
AND TIMING OF DEMONSTRATIONS

REVISION REQUESTED: N/A
CATEGORY: l-A
APPROVAL DATE: 10/05/94

The University Committee on Research Involving Human Subjects'(UCRIHS)

review of this project is complete. I am pleased to advise that the
rights and welfare of the human subjects appear to be adequately
rotected and methods to obtain informed consent are appropriate.
herefore, the UCRIHS approved this project including any revision

listed above.
RENEWAL:

REVISIONS:

.Pnosisus/

CHANGES:

If we
at (51

Sincerely

    

UCRIHS approval is valid for one calendar year, beginning with
the approval date shown above. Investigators planning to
continue a prOJect be and one year must use the green renewal
form (enclosed with t e original agproval letter or when a.
progect is renewed) to seek u ate certification. There is a
maximum of four such expedite renewals possible. Investigators
wishing to continue a project beyond that time need to submit it
again or complete review.

UCRIHS must review any changes in rocedures involving.human
subjects, prior to initiation of t e change. If this is done at
the time o renewal, please use the green renewal form. To
revise an approved protocol at any other time during the year,
send your written request to the CRIHS Chair, requesting revised
approval and referencing the project's IRE I and title. Include
in our request a description of the change and any revised

ins ruments. consent forms or advertisements that are applicable.

Should either of the following arise during the course of the
work, investigators must noti y UCRIHS promptly: (1) problems
(unexpected side effects, comp aints, e c.) involving uman
subjects or (2) changes in the research environment or new
information indicating greater risk to the human sub ects than
existed when the protocol was previously reviewed an approved.

can be of any future hel§,' lease do not hesitate to contact us
7)355-2180 or FAX (517)3 6-

171.

o Is

avid E. Wright, Ph.%23

UCRIHS Chair

DEW:pjm

CC:

Gail M.

Dummer

APPENDIX B

LETTERS OF SUPPORT

157

August 10, 1994

Mr. Kihong Kim

1518 H. Spartan Village
Michigan State University
East Lansing, MI 48824

Dear Mr. Kim:

The JUGS gun formeasuring velocity can be used by you for
your dissertation. The only problem that Ican foresee is that
you schedule its use so as not to conflict .with its use by the

YSI. '

You must be responsible for proper care of this equipment and
return it promptly when you no longer need to use it.

 

Sincerely,
course or A] W
EDUCAHON
Department at
Physical Education ii Eugene W. Brown

‘ _"‘"‘"‘ 39""? Associate Professor
Michigan State UniverSity
I M Sports Circle
East Lansing, Michigan

48824-1049 .
FAX: 1-517/353-2944 EWBill‘I'Id

158

 

 

MICHIGAN STA TE UNIVERSITY

 

DEPARTMENT OF INTERCOLLEGIATE ATHLETICS (517) 355-9710
JENISON FIELD HOUSE FAX (517) 432-1047
EAST LANSING. MICHIGAN 48824-1025

 

September 8, 1994

Mr. Kihong Kim
1518H Spartan Village
East Lansing, MI 48823

Dear Mr. Kim:

After reviewing the videotape on serve form In a wheelchair, I would

highly recommend the use of this tape for teaching beginners in the
wheelchair tennis serve. The toss, the serving, and the follow-

through can easily seen and are done properly.
Sincerely,

Stan Drobac
Former MSU tennis coach

APPENDIX C

DATA COLLECTION FORMS

159

 

FORM CHECK LIST

 

Subject's name Date

 

 

OBJECTIVE: Beginner's wheelchair tennis serve

Preparation Phase

Racket held with a eastern forehand grip.
Two wheels are in a position sideways to the net about 45 degrees.
Racket held behind head, with the elbow up.

 

(nonmment;

 

 

 

Ball Toss Phase

Tossing arm extends strait upward when player lifts the arm.

Release the ball from the tossing hand at a bit higher than forehead.
Player tosses the ball strait upward and a few inches front of the
upper body.

Player tosses the ball without spin.

A toss is as high as reach of the racket.

 

comment

 

 

 

Egecution Phase

Player leans forward a little bit while swinging to contact the ball.
The racket moves upward and forward.

Reach as high as possible in order to make contact.

The arm and racket are extended when contact is made.

Player's eyes are always on the ball.

 

comment

 

 

 

Follow-through Phase

Swing continues after racket makes contact.

Player does not put the brakes on serve, but lets it come to a smooth
stop.

Swing finishes on the opposite side from where the swing started.

160

 

STUDY 1 DATA COLLECTION FORM

 

Subject's name Date

 

Birth Date / /

Telephone If I

Group Classification: Wheelchair Model Stand-up Model
(Circle) No Model

Test: ball placement(accuracy) and ball velocity in the wheelchair tennis
serve.

Mark for placement

O=ball lands on serve box W=wide L=long N=under the net

PRETEST POSTTEST

Trial No Velocity(mph) Placement Velocity(mph) Placement

1

 

Average mph Total [10 Average mph Total [10

 

Test: form evaluation in the wheelchair tennis serve.

Pretest score /16 Posttest score /16

161

 

STUDY 2 DATA COLLECTION FORM

 

Subject's name Date

 

 

Test: ball velocity and ball placement (accuracy) in the wheelchair tennis
serve.

Mark for velocity: MPH
Mark for placement:0=ball lands on serve box, W=wide, L=long, N=under the

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

net
Test#( ) Test#( ) Test#( )

Velocity Accuracy Velocity Accuracy Velocity Accuracy

1

2

3

4

5

6

7

8

9

10

AVG

Test#( ) Test#( ) Test#( )

Velocity Accuracy Velocity Accuracy Velocity Accuracy

1

2

3

5

7

8

9

10

 

 

 

 

 

162

 

SUBJECT INFORMATION SHEET FOR STUDY 2

 

Subject Name

 

Date of Birth / / Gender

 

 

Address

 

Phone

 

Information about physical condition

1. Type of disability:

2. Years of disability:

3. Comments about mobility of upper body (trunk, head, arm,
hands, and fingers):

Sportsyexperience

1. Past sports experience:

2. Sport activities engaged on a regular basis:

APPENDIX D

RAW DATA

163

 

STUDY 1 DATA

 

0101
0102
0103
0104
0105
0106
0107
0108
0109
0110
0111
0112
0113
0114
0115
0201
0202
0203
0204
0205
0206
0207
0208
0209
0210
0211
0212
0213
0214
0215
0301
0302
0303
0304
0305
0306
0307
0308
0309
0310
0311
0312
0313
0314
0315

31.6
38.0
30.0
48.4
30.9
30.8
32.4
37.4
27.8
27.8
29.1
29.0
32.8
24.4
28.5
35.2
27.8
56.8
32.8
38.3
43.7
46.7
34.7
24.8
27.8
32.6
24.4
25.4
27.7
23.0
37.5
36.7
43.5
33.7
44.4
38.9
32.1
24.0
31.1
42.2
30.4
21.4
32.5
18.3
26.8

37.2
41.0
36.1
52.2
40.8
36.1
41.4
40.0
28.8
25.5
26.1
28.1
26.2
25.0
30.7
44.9
36.2
56.1
41.3
37.0
42.2
51.6
34.4
26.6
27.8
35.9
36.0
36.8
27.7
23.2
35.1
44.3
52.7
35.0
51.6
41.3
43.1
33.6
30.3
38.9
35.8
25.0
49.4
24.3
38.6

18.8
37.5
25.0
62.5
25.5
25.5
25.5
68.8

50.0
62.5
75.0
81.3
56.3
81.3
87.5
81.3

50.0100.0

31.3
31.3
18.8
62.5
18.8

37.5
75.0
81.3
81.3
62.5

75.0100.0

37.5
18.8
75.0
31.3
25.5
31.3
56.3
25.0
18.8
18.8
75.0
25.5
18.8
43.8
31.3
62.5
56.3
56.3
25.0
50.0
25.0
25.0
12.5
37.5
75.0
31.3
37.5
75.0
12.5
31.3

81.3
37.5
75.0
56.3
43.8
50.0
75.0
37.5
25.0
56.3
75.0
56.3
31.3
56.3
56.3
68.8
68.8
68.8
31.3
56.3
43.8
50.0
31.3
37.5
81.3
68.8
31.3
93.8
12.5
62.5

COOCOOOOOOOOOOOOOOOOOOOOOOOOOOt-‘t—‘t-tHHI—‘t—It-‘t-It-‘t-‘t-lt-‘I-‘l-I

OOOOOCOOOOOOOOOHHI—IHHHHHHHHHHHHOOOOOOOOCOOOOOO

I—IHHHHHHHHHI—‘t—‘t—‘HHOOOOOOOCOOOOOOOOOOOOOOOOOOOOOO

NMNNNNNI—‘I—‘I—‘I—iHHI—‘t—‘NNNNNNNI—‘HHHI—‘I—IHI—‘NNNNNNNI—‘i—‘I—‘I—‘I—‘I—‘I—‘H

 

C1:
C2:
C3:
C4:
C5:
C6:
C7:
C8:
C9:

164

ID
VELOCITY (PRETEST)

VELOCITY (POSTTEST)

PLACEMENT % (PRETEST)

PLACEMENT % (POSTTEST)

FORM % (PRETEST)

FORM % (POSTTEST)

TREATMENT (1=WHEELCHAIR MODEL, 0=DUMMY)
TREATMENT (1=STAND-UP MODEL, 0=DUMMY)

C1 0 : TREATMENT ( 1=NO MODEL , 0=DUMMY)
C11: GENDER (1=MALE, 2=FEMALE)
C12: AGE

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