RELATIONSHIP BETWEEN THE OBSERVATION OF TYPES OF SCAPULAR
DYSKINESIS AND PEAK MUSCLE ACTIVITY OF THE SCAPULAR STABLIZING
MUSCLES

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

by
Jenna Sherman

Research Advisor, Dr. Edwin Zuchelkowski
California, Pennsylvania
2010

ii

iii

ACKNOWLEDGEMENTS
My thesis has been thought of and created by many sources
of motivation in my life. Throughout this entire process I
have received support from my professors, classmates,
undergraduates, as well as the baseball team. I thank you all
for putting up with the rollercoaster ride of up‟s and down‟s
that have come along with this whole project.
Thank you Dr. Zuchelkowski for your advice and wisdom on
the anatomy of the shoulder and for all of your time spent
guiding my research. I appreciated your positive attitude that
this would get done on time. You‟ve been a great help this
year.
Thank you Dr. Hess for you extensive knowledge of
statistics and you‟re ability to explain this all in a way
that makes sense. I have learned more about research and how
to interpret data this year than I ever dreamed I would know.
Your positivity and drive to learn more has motivated me in
many areas.
Thank you Dr. West for your knowledge and wisdom of EMG
and data analysis, this was truly a team effort. Your comedic
relief and positivity helped me get through this process in
one piece. Thanks for always helping to find a solution.

iv
TABLE OF CONTENTS
Page
SIGNATURE PAGE

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

AKNOWLEDGEMENTS . . . . . . . . . . . . . . . . iii
TABLE OF CONTENTS
LIST OF TABLES

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

LIST OF FIGURES .
INTRODUCTION
METHODS

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

. . . . . . . . . . . . . . . viii

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

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

RESEARCH DESIGN. . . . . . . . . . . . . . . . 5
SUBJECTS

. . . . . . . . . . . . . . . . . . 7

PRELIMINARY RESEARCH

. . . . . . . . . . . . . 8

INSTRUMENTS . . . . . . . . . . . . . . . . . 8
PROCEDURES

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

HYPOTHESES

. . . . . . . . . . . . . . . . . 19

DATA ANALYSIS
RESULTS

. . . . . . . . . . . . . . . . 19

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

DEMOGRAPHIC DATA . . . . . . . . . . . . . . . 20
HYPOTHESIS TESTING

. . . . . . . . . . . . . . 21

ADDITIONAL FINDINGS . . . . . . . . . . . . . . 23
DISCUSSION . . . . . . . . . . . . . . . . . . 28
DISCUSSION OF RESULTS . . . . . . . . . . . . . 29
CONCLUSIONS . . . . . . . . . . . . . . . . . 34
RECOMMENDATIONS

. . . . . . . . . . . . . . . 37

v
REFERENCES . . . . . . . . . . . . . . . . . . 40
APPENDICES . . . . . . . . . . . . . . . . . . 42
APPENDIX A: Review of Literature

. . . . . . . . . 43

Introduction . . . . . . . . . . . . . . . . . 44
Anatomy of the Scapula . . . . . . . . . . . . . 45
The Glenohumeral Joint

. . . . . . . . . . . . 48

The Scapulothoracic Joint

. . . . . . . . . . 50

Scapular Dyskin esis . . . . . . . . . . . . . 52
Biomechanical Factors . . . . . . . . . . . . 54
Electromyographic Activity and Scapular Movement 59
Function of the Scapular and Glenohumeral Joint 61
Summary . . . . . . . . . . . . . . . . . . . 64
APPENDIX B: The Problem . . . . . . . . . . . . . 66
Definition of Terms . . . . . . . . . . . . . . 68
Basic Assumptions . . . . . . . . . . . . . . . 69
Limitations of the Study . . . . . . . . . . . . 69
Delimitations of the Study . . . . . . . . . . . 70
Significance of the Study. . . . . . . . . . . . 70
APPENDIX C: Additional Methods .

. . . . . . . . . 72

Informed Consent Form (C1) . . . . . . . . . . . 74
IRB: California University of Pennsylvania (C2) . . . 77
Individual Data Collection Sheet (C3) . . . . . . . 89
Figures and Tables

(C4) . . . . . . . . . . . . 91

Demographic Information (C5)

. . . . . . . . . . 96

vi
ABSTRACT

. . . . . . . . . . . . . . . . . . 98

REFERENCES . . . . . . . . . . . . . . . . . . 100

vii

LIST OF TABLES
Table

Title

Page

1

Descriptive Mean Statistics . . . . . . . 21

2

Effect of Peak Muscle Activity
During Exercises on Types of Dyskinesis . . 22

3

Type of Dyskinesis and Athlete Position . . 26

4

Electrode Placement and MVIC Test
Positions for Normalization of EMG . . . . 95

5

Descriptive Statistics . . . . . . . . . 96

6

Means and Peak Percentage Values for Each
Muscle and Exercise . . . . . . . . . . 98

viii
LIST OF FIGURES
Figure

Title

Page

1

Push-Up-Plus Start Position

.

.

.

11

2

Push-Up-Plus End Position.

.

.

.

11

3

Lawn-Mower Start Position.

.

.

.

13

4

Lawn-Mower End Position. .

.

.

.

14

5

Electrode Set-Up.

.

.

.

.

17

6

Electrode Set-Up with SA .

.

.

.

17

.

1

INTRODUCTION

The shoulder complex is very intricate and includes
articulations at the acromioclavicular joint, sternoclavicular
joint, glenohumeral joint, as well as the scapulothoracic
articulation. Technically, the scapulothoracic articulation is
not a true joint, but scapular movement plays a large role in
glenohumeral rhythm.1 The shoulder has the largest degree of
freedom compared to other joints in the body, but this freedom
comes with a loss of stability. This puts increased stress on
dynamic stabilizers such as the rotator cuff and static
stabilizer such as the glenoid labrum. The articulations which
make up the shoulder complex, need to be functioning properly
to avoid injury and to ensure maximum athletic performance.2
Overhead sports which require overhead motion past 90°
such as swimming, volleyball, baseball, and softball demand
more of the shoulder complex because of the nature of the
sport. Since these sports require repetitive overhead motion
of the shoulder, if the articulations are not working
properly, an injury is likely to occur. If the movements
through the kinetic chain are not completed appropriately and
failure occurs at some point, it could be for many reasons.
Biomechanical, musculature, ligament, bone, and nerve issues

2
could all be a culprit for putting the athlete at risk for
injury.3 Because of the complexity of shoulder movement;
certified athletic trainers must understand the kinetic chain
concept and master the anatomy to be able to accurately assess
any injury.
A common shoulder dysfunction that has been observed is
scapular dyskinesis, which can be defined as: “an alteration
in the normal position or motion of the scapula during coupled
scapulohumeral movements”.4 The scapula needs to maintain
proper alignment along the thoracic wall in order to stabilize
the glenohumeral joint and allow transfer of forces through
the shoulder. Causes of dyskinesis may be from bony
malalignment, muscular imbalance, or a loss of
protraction/retraction control. If scapula function is altered
entire kinetic chain can be affected by changing the force on
the glenohumeral and elbow joints, decrease the efficiency of
the rotator cuff and possibly result in impingement,
instability, and labral injuries.1
The muscles that have been shown to be most important for
scapular stabilization are the rhomboids, serratus anterior,
lower trapezius, and upper trapezius.1,5 The serratus anterior
originates along the first 7-10 ribs and the intercostal
muscles, and inserts under the scapula on the lower medial
scapular border.6 The trapezius is a broad, triangular muscle

3
originating from the occiput of the skull to the lower
thoracic spine and inserting onto the clavicle, acromion, and
spine of the scapula.
The serratus anterior and lower trapezius have been found
to be most susceptible to inhibition and a likely cause for
muscle related scapular dyskinesis. The serratus anterior,
rhomboids, and lower trapezius make up the crucial lower force
couple and are responsible for the inferior stabilization as
well as upward rotation of the scapula.5,6 These muscles work
together to control retraction and general stability of the
scapula.5
Inhibition can result in a loss of force generated by the
muscle and an alteration in the normal muscle firing and
muscle coupling in the shoulder.1 Through rehabilitation and
implementation of Moseley scapular core exercises, the
surrounding muscles of the scapula can regain their activity.6
The Moseley core exercises which have shown to generate the
most activity of scapular stabilizers in healthy subjects
include; push-up plus, low row, press-up, and scaption.6
Moseley‟s core exercises can be found within many scapular
rehabilitation programs, but there are many more exercises to
choose from that activate the scapular stabilizers.
The lower trapezius has been shown to be weak in common
shoulder injuries and is often difficult to target with

4
exercises. The lawnmower exercise, with the pulling motion,
has been effective at activating the lower trapezius to
clinically moderate levels as well as activating the upper
trapezius and serratus anterior.5 The serratus anterior has
been shown to be weakened with injured throwers and this is
thought to be because of a change in activation patterns while
in motion. The push-up plus exercise has been found to be able
to activate the serratus anterior to very high levels.6 The
shoulder-shrug exercise has been most effective at producing
the greatest amount of electromyography (EMG) activity within
the upper fibers of the trapezius.6
The purpose of this study was to analyze EMG activity of
the serratus anterior, upper trapezius, and lower trapezius
during selective exercises in individuals with normal and
abnormal scapular motion. An observational descriptive study
between EMG activity and three types of scapular dyskinesis
will be performed. It is anticipated that specific scapular
stabilizing muscles would show a decrease in activity,
resulting in scapular dyskinesis. Additionally, the study
examined if a relationship exists between muscle activity and
types of scapular dyskinesis.

5
METHODS

The purpose of this study was to determine if
decreased scapular stabilizing muscle activity as shown by
electromyographic (EMG) analysis would lead to types of
scapular dyskinesis. This information can be found by
comparing the observation of four groups of scapular
dyskinesis with EMG activity readings of the serratus anterior
(SA), lower trapezius (LT), and upper trapezius (UT).
The following is discussed: Research design, Subjects,
Preliminary Research, Instruments, Procedures, Hypothesis, and
Data Analysis.

Research Design

This study was an observational descriptive study design.
There were three independent variables; serratus anterior,
lower trapezius, and upper trapezius peak percentage of muscle
activity during the two exercises. The peak percentage was
found by dividing the maximal voluntary isometric contraction
(MVIC) by the peak activity of each muscle during both
exercises. The trend between types of scapular dyskinesis and
muscle activity was found with the subject‟s mean value from
each muscles average peak contraction for each exercise and

6
compared with what type of dyskinesis they were categorized
as.
Two independent variables were utilized in this study.
The first was the independent between subject‟s variable of
type of scapular dyskinesis. There was a grading scale of four
types of scapular dyskinesis: Type 1: prominence of the
inferior medial scapular border and is primarily an abnormal
rotation around a transverse axis; Type 2: prominence of the
entire medial border and represents abnormal rotation around a
vertical axis; Type 3: superior translation of the entire
scapula and prominence of the superior medial scapular border;
and Type 4: none, presenting with symmetrical scapular
movement.4,5 The second independent variable was the within
subject variable of exercises performed during the EMG
testing; the lawnmower exercise, and the push-up-plus. By
measuring EMG activity of the serratus anterior, upper
trapezius, and lower trapezius we were able to observe any
decrease in firing and compare those results with the type of
scapular dyskinesis the subject presented with to find a
trend.

7
Subjects

Subjects included 22 NCAA Division II Baseball players.
Overhead athletes were defined as athletes participating in
any sport which requires arm movement beyond 90° of humeral
abduction. The subjects were Division II collegiate studentathletes from California University of Pennsylvania. The
inclusion criteria included:
(1)

Being a collegiate overhead athlete

(2)

Between the ages of 18-30

(3)

Have full clearance from a physician to participate
in their sport

(4)

No history of shoulder surgery within the last six
months.

With this study being observational there was not very
much physical activity demanded of the subject creating a very
low risk of injury. Demographic information was gathered via a
data collection sheet and included: (1) Weight (either over or
under 150 pounds), (2) Sport played, (3) Position played, and
(4) Dominant arm. An informed consent was read and signed by
each participant prior to the beginning of the study (Appendix
C1).

8
Preliminary Research

The purpose of preliminary research was to familiarize
the researcher with the procedures of the EMG equipment. In
order to conduct this study effectively, it was necessary for
the researcher to become efficient in experiment set-up,
become quick with appropriate EMG electrode placement, and be
able to effectively communicate directions. Additionally, the
preliminary research allowed the researcher to determine
approximate time for each subject to complete the study, which
took approximately forty minutes.

Instruments

The researcher used a demographic sheet (Appendix C5) to
determine dominant arm, position played, sport played, and
weight for either over or under 150 lb. The study used the
following equipment: Theraband® [Akron, OH] (green and black),
5lb dumbbell, 3lb dumbbell, Biopac MP150® [Goleta, CA], pregelled disposable Ag-AgCl surface electrodes with a diameter
of one centimeter, and a metronome.
Identifying Scapular Dyskinesis
The movements performed for the identification of types
of scapular dyskinesis included horizontal humeral abduction

9
in the sagittal, frontal, and 45° in-between sagittal and
frontal planes. The subjects‟ movements were recorded in the
data collection sheet by the observations of the researcher.
The dumbbells were used for resistance to accentuate any
presentation of scapular dyskinesis with the athlete. The
metronome was used to keep track of speed regulation during
the movements; subjects were given three beats up and three
beats down.9

Exercise Testing
For exercise testing the subjects used Therabands® of
medium resistance (green) for warm-ups before the EMG analysis
with the sagittal, frontal, and 45° in-between with thumbs-up
and thumbs-down arm raises. The exercises for the EMG analysis
included the lawnmower exercise, and push-up plus (Figure 1
and 2). These exercises were selected based on their ability
to target the serratus anterior and lower trapezius muscles
during activity.5,6 The serratus anterior and lower trapezius
form an important force couple with the translation of the
scapula and both have been shown to have decreased activity in
subjects presenting with scapular dyskinesis.5 The metronome
was utilized while performing the exercises for the EMG
analysis as well as the exercises for scapular dyskinesis in
order to control for time taken to complete the movements.

10
This timing for the metronome was three beats up and three
beats down.9 The exercises were repeated five times each with
the repetitions being averaged for one value. If exercises
were not completed as directed, that repetition was thrown-out
and the exercise was repeated until five complete repetitions
were gathered.

Push-up Plus Exercise
The push-up plus is a multijoint exercise that takes the
common pushup a little bit further. The participant starts
with hands shoulder width apart, fingertips facing forward,
back straight, and legs together with body weight on toes. The
subjects perform a regular push-up keeping elbows into the
side of the torso while lowering body to the ground. When
their chest hit the floor surface they were instructed to
begin pushing body weight up, when their elbows got to the
extended position, they were asked to push their body a little
further up by protracting the scapulas and rounding shoulders
toward the ground. (Figures 1 and 2)

11

Figure 1. Start of Push-Up-Plus

Figure 2. End of Push-Up-Plus

12
Lawnmower Exercise
The lawnmower exercise is a multijoint exercise that
mobilizes joints in a diagonal pattern from the contralateral
leg through the trunk to the ipsilateral arm. These multijoint
exercises use force-dependent integrated muscle activation
patterns to coordinate the motions of connected joints and to
produce efficient and stable distal joint positions though the
production of interactive moments. They have been found to
generate higher gains in strength than single joint exercises
because of the facilitation of the force-dependent patterns by
increase in neurological activity.5 This exercise used the
motion of hip/trunk extension, trunk rotation, and scapular
retraction to activate the muscles to assist in positioning
the scapula in retraction.
Targeted muscles for the lawnmower exercise were the SA
and LT.5 Although the SA is often characterized as a scapular
protractor, a major component of scapular retraction, the SA
is oriented to maintain this position. This is demonstrated by
high and early levels of activation as is seen in cocking
(scapular external rotation) in baseball, tennis, and arm
elevation. It is also shown by the fact that scapular position
in long thoracic nerve palsy is one of internal rotation and
anterior tilt, which is more characteristic of loss of
external rotation control.1,7 For this study, subjects began

13
the exercise with their trunk flexed and rotated to the
contralateral side from the instrumented arm with their hand
at the level of their contralateral patella. Subjects were
instructed to rotate the trunk toward the instrumented arm and
extend the hip and trunk to a vertical orientation while
simultaneously placing their instrumented arm at shoulder
level. Body movement was smooth, but the retraction position
was to be completed with a strong contraction of the muscles.5
For this study resistance with a grey Theraband® was used to
allow for improved EMG readings from the tested
muscles.(Figures 3 and 4)

Figure 3. Start of Lawnmower Exercise

14

Figure 4. End of Lawnmower exercise

EMG Data
In collecting the EMG data, the researcher used four
channels from a Biopac MP150® electromyography machine. Three
channels were designated for the muscles tested and the other
channel was connected to an electronic biaxial goniometer. The
Biopac MP150 was connected to a Microsoft Windows based
personal computer with the Biopac‟s AcqKnowledge® program
[Goleta, CA] to collect and analyze the data. The study

15
utilized pre-gelled disposable Ag-AgCl surface electrodes with
a diameter of one centimeter. The electrodes were placed on
their dominant arm over the motor points of each muscle belly
with a center-to-center spacing of 2.5 centimeters.5 The
goniometer was applied to the subject‟s elbow for both EMG
analysis exercises to measure the beginning and end degree of
movement.
The raw EMG signal was band pass filtered at 10 and 1000
Hertz (Hz). The researcher utilized a sampling rate of 100 Hz
using the AcqKnowledge software. The signals were rectified
and normalized before the data analysis was completed. Peak
percentage of muscle activity was found from dividing the
values of each muscle during MVIC and dividing it by the
values found from the same muscle during each exercise.
(Appendix C4, Table 4)

Procedures

These subjects first signed the informed consent and
answered questions about position and arm-dominance. Anyone
who had a pre-existing condition or surgery to either arm in
the past six months was disqualified. The researcher was also
the certified athletic trainer for the team so all preexisting conditions were known. This did not however affect

16
the team with volunteering; they were able to sign-up on a
sheet posted outside of the door during treatments without any
pressure.

Identifying Types of Scapular Dyskinesis
The subjects first performed the identifying types of
scapular dyskinesis portion of the study. Type of scapular
dyskinesis was categorized by instructing the subject to
perform humeral horizontal abduction in three planes. With
this data collected the subjects were asked to hold either 3lb
or 5lb dumbbells, according to the subject‟s body weight. If
they were less than 150 lbs they took the 3 lb. weight, if
they were over 150 lbs they took the 5 lb. weight. This weight
was added to accentuate any abnormal movement of the scapula
that may be produced.9,11 It has been stated in previous
research that muscular fatigue may directly affect
scapulohumeral rhythm, resulting in compensatory increased
rotation or destabilization of the scapula, which suggests the
need to assess with resistance.9 The subjects were visually
assessed one time by a certified athletic trainer while
performing humeral horizontal abduction in the frontal and
sagittal plane, as well as at 45° in-between frontal and
sagittal with thumbs up and down. These movements did not go
above 90° to avoid irritation of the supraspinatus.

17

Electromyographic Analysis
After the movements for identifying types of scapular
dyskinesis, the athletes had EMG electrodes placed on the
serratus anterior (SA), upper trapezius (UT), and lower
trapezius (LT). These muscles were chosen because of previous
research showing they are the most important muscles in force
couples that control scapular position and motion.5 (Figure 5
and 6)

Figure 5. Electrode Set-Up

Figure 6. Electrode Set-Up

Before testing, each subject performed a warm-up routine
consisting of Theraband® exercises with medium resistance

18
bands. These exercises included; low-row, frontal and sagittal
plane horizontal arm abduction, and arm extension.
Placement of the electrodes and position of exercise is
described in appendix C4, table 4. The positions where chosen
for the

MVIC based on their performance to best isolate each

respective muscle based on standard muscle strength testing
positions.5

Five MVICs for each muscle were performed for

three-seconds and then the peak was recorded in order to
gather normalization of EMG data and also to provide a
reference of electrical activity for each muscle.
The two exercises used to analyze EMG activity of the
muscles included the push-up plus (PUP), and lawnmower (LM).
Subjects practiced the exercises before the testing to become
comfortable with the correct performance movements. Time was
kept by a metronome and subjects were given three beats up and
three beats down to complete the exercise.9 Verbal feedback
was given by the researcher for correction of exercise. The
subjects were instructed to perform each exercise five times.
If any exercise was not performed correctly, additional
repetitions were added on until five correct exercises were
performed.5 The addition of a one or two exercises occurred
approximately three times with two subjects.

19
Hypotheses

The following hypotheses were tested with this study:
1) There will be a decrease in peak muscle activation of the
serratus anterior, upper trapezius, and lower trapezius
during exercises (2) performed depending on scapular
dyskinesis (4).
2) There will be a relationship between specific muscle
inactivity and the presentation of a certain type of
scapular dyskinesis.

Data Analysis

All data will be analyzed by SPSS version 17.0 for
Windows at an alpha level of ≤0.05.

The research hypotheses

will be analyzed using a 4x2 Factorial MANOVA. (Table 2) All
EMG scores were reported as percentage of maximal voluntary
contraction. There will also be descriptive statistical
information reported with the means of the peak muscle
contractions from all three muscles during both exercises
compared with the grouping of the subjects into types of
scapular dyskinesis. (Table 1)

20
RESULTS

The purpose of this study was to determine if any of four
types of scapular dyskinesis would correlate with a decrease
of peak muscle activity from the muscles tested during two
exercises. The following section contains the data collected
through the study and is divided into three subsections:
Demographic Information, Hypotheses Testing, and Additional
Findings.

Demographic Information

There were 22 physically active, healthy subjects who
participated in this study. The age range was from 18-23 years
old. All 22 subjects were active members of the California
University of Pennsylvania baseball team consisting of 10
pitchers (45%) and 12 position players (56%). Of these players
18 (82%) were right handed, the remaining 3 (18%) were left
hand dominant.

21
Hypothesis Testing

The following hypotheses were tested in this study.

All

hypotheses were tested with a level of significance set at α ≤
0.05.

A 4x2 repeated measures factorial ANOVA was calculated

for the effect of muscle activity on types of scapular
dyskinesis observed. Descriptive statistics were used to find
a trend between peak muscle activity of the three scapular
stabilizers; serratus anterior, lower trapezius, and upper
trapezius. (Table 1) A complete list of raw statistics is
listed in Appendix C4 under table 5.

Table 1. Descriptive Mean Statistics
Type

Exercise 1 Lawnmower
Peak SA Peak LT Peak UT

Exercise 2 Push-Up-Plus
Peak SA Peak LT Peak UT

1

1.67

1.43

1.3

1.77

3.77

2.56

2

1.5

1.5

1.15

.077

5.03

0.37

3

2.1

2.4

2.2

1.3

1.7

1.75

4

1.03

2.05

1.25

4.1

1.7

1.21

Hypothesis 1: There will be a decrease in peak muscle
activation of the serratus anterior, upper trapezius, and
lower trapezius during exercises performed depending on
scapular dyskinesis.

22
A 4x2 factorial MANOVA was calculated examining the
effect of peak muscle activity of the serratus anterior, upper
trapezius, and lower trapezius during two exercises on types
of scapular dyskinesis observed. (Table 2)

Table 2. Effect of Peak Muscle Activity* During Exercises on
Types of Scapular Dyskinesis
Effect

Value

Exercise

.887

Type

Hypothesis df

Error df

Sig.

3

34

.246

.701

9

82.898

.181

Exercise and Type .696

9

82.898

.170

*Activity in serratus anterior, lower trapezius, and upper
trapezius.

Conclusion:

No significant effect was found between

exercises and peak activity of the muscles tested
(Lambda(3,34)=.887, p/>.05), or between type of dyskinesis and
peak activity of the muscles tested (Lambda(9,82.9)=.701,
p/>.05). No significant effect was found between the
interactions of peak muscle activity and exercises or types of
scapular dyskinesis observed (Lambda(9, 82.9)=.696, p/>.05).

23
Hypothesis 2: There will be a relationship between
specific muscle peak activity and a certain types of scapular
dyskinesis.
Conclusion: There was an analysis of descriptive
statistics comparing means of peak muscle activity of the
three scapular stabilizing muscles during the two exercises
with the four types of scapular dyskinesis which the subjects
were put into. (Table 1) With the descriptive mean statistics
there was a trend found between a decrease in lower trapezius
peak activity during the lawnmower exercise with type one and
two dyskinesis. For those who presented with scapular
dyskinesis all of their serratus anterior peak activity during
the push-up plus exercise was lower compared with the nondyskinesis group. There was also an increase in peak activity
of the upper trapezius during the lawnmower within the type
three group compared with other groups.

Additional Findings

There were not any statistically significant findings for
the first hypothesis; there were however a few observations
made throughout the study by the researcher. Hypothesis two
had an observation of a few trends between mean peak muscle

24
activity of certain scapular stabilizers and those presenting
with certain types of scapular dyskinesis. Although this data
was not collected, there was a pattern of non-dominant
scapular dyskinesis present in those who did not present with
dyskinesis in their dominant arm. The reason for this
observation of non-dominant dyskinesis is not quite clear and
there is not literature supporting this finding. This was
mostly found with those who were right hand dominant; their
left scapula would have a medial border or inferior angle
prominence. Their dyskinesis type is consistent with type 1
and type 2, not the more involved type 3 which is superior
upward rotation and found to be present in 100% of those with
chronic instability and common among those with impingement as
well.4 From those who were observed to have non-dominant arm
scapular dyskinesis all were position players. Of those
position players many were pitchers in high school, but not
starters. The altered demands of the sport, increased
attention to scapular stabilizing strength in the weight room,
and focusing on mechanics when they made the transition to DII
sports could be the reason their dominant arm presents without
scapular dyskinesis. The reason why their non-dominant arm
would present with dyskinesis though needs further
investigation.

25
Another observation was that of the three subjects
recorded as having type two scapular dyskinesis (medial border
prominence) all of them were position players. This finding
was not unusual because most overhead athletes will present
with medial border prominence, but it was interesting that all
of the subjects were position players.13 Because of literature
supporting medial border prominence in overhead athletes I was
surprised that only three subjects (13.64%) presented with and
that a majority of the subjects (59.1%) presented without any
scapular dyskinesis at all. This could be due to the fact that
they all participate in a weight lifting program which focuses
on scapular stabilizing exercises, and our strength and
conditioning coach is aware of the importance of scapular
stabilizers and their relationship with the kinetic chain.
Of the three subjects recorded as having scapular
dyskinesis type 3 (superior border elevation) all were
pitchers.(Table 3) The type 3 dyskinesis has the most
potential for causing future shoulder injuries because when
the scapulas anterior tilt around the horizontal axis is
altered it affects the acromion process and its relationship
with the humerus in the subacromial space. When the scapula
has early movement with anterior tilting it causes the
superior border to elevate which can lead to the timing and
magnitude of acromion motion changing, the distance of the

26
subacromial space being altered, the angle of the glenohumeral
arm may be increased, and maximal muscle activation may be
decreased.7 Within this study there were not any subjects who
presented with any shoulder problems.

Table 3. Type of Dyskinesis and Athlete
Type of Dyskinesis

Pitcher

Position

Type 1

2

1

Type 2

0

3

Type 3

3

0

Type 4

5

8

Another observation while doing this study was that the
senior pitcher who has had many shoulder problems in years
past did not present with any scapular dyskinesis. He throws
almost every day and does not complain of any pain beside the
occasional tightness. From the intensity of his daily training
plan and history of injury it would seem as though he would
have scapular dyskinesis. However, he performs scapular
exercises everyday and makes sure that everything is proper
form, even his posture. After he had those shoulder problems
his physical therapist taught him the importance of the
scapula with shoulder function and that he has to do those

27
exercises to stay healthy enough to throw. Although the entire
team is exposed to scapular strengthening exercises, they do
not do them every day or keep a straight posture throughout
the day either. If a program were introduced to the baseball
team for scapular muscle strengthening and enforced daily
there could be the possibility that other pitchers would
experience the same positive effects that the one has had
throughout the past two seasons.

28
DISCUSSION

The purpose for this study was to examine the difference
of the primary scapular stabilizing muscles activity; serratus
anterior, lower trapezius, and upper trapezius during two
exercises, observing for four types of scapular dyskinesis
which have been identified in previous research. The second
hypothesis for this study was developed with the idea that
there would be a significance found between certain muscle
peak activity and types of dyskinesis; if a person presented
with a weak lower trapezius they would be more likely to
present with a specific type of dyskinesis. With that
prediction the purpose for this study was to find what
muscular weakness would present with what kind of dyskinesis
so that when an athlete presents with that type we can present
a protocol for them specific to certain muscle groups. By
determining a relationship between certain muscular imbalances
from the stabilizing scapular muscles with a certain type of
dyskinesis there could have been more specific protocols for
those presenting with dyskinesis. The following section is
divided into three subsections: Discussion of Results,
Conclusions, and Recommendations.

29
Discussion of Results

Upon completion of this study it was found that muscle
activation patterns of the primary stabilizing muscles of the
scapula during the two exercises was not significantly
related, but showed a trend on types of scapular dyskinesis
observed. Recent literature has focused on the relationship of
scapular movement being related to shoulder function and
possibly leading to shoulder injuries if scapular dyskinesis
is present.1 It is hard to determine the exact relationship of
the scapula and shoulder because there are so many other
factors that play a role in the biomechanical function of the
upper extremity.1,4 By continuing to learn more about the
relationship between scapular movements and the shoulder there
might be a protocol developed to prevent possible injury to
the shoulder and elbow. With overhead athletes it is important
that proper mechanics of the entire kinetic chain is taught in
order for complete transfer of forces from the legs to the
trunk through the shoulder and elbow to the hand, which will
also help them avoid injury.4
By using a sample of overhead athletes who are all
currently participating in DII athletics and uninjured it
seemed likely that there would be a significant relationship
between peak muscle activity and types of scapular dyskinesis

30
in order to better understand why the dyskinesis occurs. The
athletes included were all from the baseball team and tested
during their in-season. The sample included pitchers and
position players in order to do a comparison in Post Hoc
testing if any significance was found. However, it was later
realized that although some of the players are now position
only, many of them were once pitchers in high school.
There is research stating that overhead athletes will
present with some abnormalities on their dominant side because
of stretching of the surrounding tendons and ligaments, but
that has only been shown to affect the dominant shoulder
presenting as lower than the non-dominant.12 With this in mind,
it made sense that they may present with scapular dyskinesis
from the altered shoulder position, but this study did not
find that to be true.
This study involved a limited subject base which was all
baseball players and almost all with pitching backgrounds.
With other sports involved in the study such as tennis,
volleyball, and swimming the results would include athletes
who have altered muscular demands of their arms and therefore
may present with different findings than just one population.13
Previous research supporting the fact that gender does not
have a significant effect on scapular positioning makes the
inclusion of men only more acceptable.13

31
Another possible reason for not finding significant
values with the first hypothesis would be that there is human
error involved in the study as well as other variables. During
the MVIC testing the researcher may not have provided enough
resistance to engage the muscle to full potential which might
explain why many values for the peak activity for exercises
are over 100%. These values can be found in table 6 in C4.
While performing the exercises there also could have been
error with the electrodes coming off the skin and therefore
disrupting the EMG reading for that muscle. There were steps
taken such as cleaning the skin surface and taping the
electrodes to the skin to prevent them from peeling off; but
when the subjects moved around, it was especially difficult to
keep the lower trapezius electrodes on because of the medial
border of the scapula translation. Mathematical error was
minimized from entering all data into SPSS version 17.0 and
finding the statistics from the data output.
The purpose of this study was to find a difference
between the three primary scapular stabilizing muscles and
identifying three types of scapular dyskinesis. The results
from the 4x2 MANOVA statistical analysis showed that there was
not a significant finding between any of the variables. The
results were a little frustrating because they went against
what the literature suggests would be true. From past research

32
done with the importance of strengthening the surrounding
scapular musculature it would make sense that if there were to
be a decrease in muscle activity the subject would be more
likely to present with scapular dyskinesis.5,6 The recent
literature describing three types of scapular dyskinesis
supports the idea that there must be a reason why the scapula
presents with different patterns of abnormality.9,11 The
explanation behind the identification of the types of scapular
dyskinesis is missing from literature. This study was focused
on the possibility of a difference in scapular stabilizer
activity of individuals grouped into three types of scapular
dyskinesis compared with a non-dyskinesis group for the reason
of why subjects present with different types of scapular
dyskinesis. After not finding any statistical significance
with the 4x2 Factorial MANOVA there was a descriptive mean
statistical analysis done to figure out more with the second
hypothesis.
Although the first hypothesis did not have statistical
support, there was still a lot of information gathered and
this can show us as athletic trainers that the scapula needs
to be taken into consideration with shoulder preventative and
rehabilitative programs. From the descriptive mean statistics
with the second hypothesis, we can see there is a trend
between those presenting with lower trapezius weakness and

33
type one and two scapular dyskinesis.(Table 1) There was also
a trend that from the dyskinesis group, type two had the
lowest peak lower trapezius activity during the push-up plus
exercise. This makes sense because the lower trapezius allows
for the translation of the center of rotation for the scapula
and provides a straight-line pull for scapular rotation.1,9 If
the scapula is not able to translate properly or cannot
maintain stabilization along the medial border the inferior
angle and medial border will become more prominent. There is
also a trend between all types of scapular dyskinesis
presenting with a decrease peak activity of the serratus
anterior. (Table 1) The serratus anterior plays a role as an
external rotator of the scapula as well as preventing scapular
winging by anchoring the scapula to the underlying ribs.1,9
With the type three dyskinesis group there was a trend of an
increase in activation of the upper trapezius which would
create the superior border elevation that distinguishes type
three.1,9 The descriptive mean statistics of the peak values
have helped determine there is a trend between muscle activity
during the lawnmower and push-up-plus exercise and subjects
presenting with different types of scapular dyskinesis but
further research needs to be done to determine the exact
relationship.

34
Scapular strengthening programs should still take
athletes into individual consideration such as sport specific,
any shoulder injuries, or other issues that they may have
experienced or are experiencing. When programs are not
individualized they could be overlooking deficits of some
muscles groups and overworking the dominant muscle groups
which could prolong the healing process even longer or not
taking into consideration injury history. These muscle groups
may not even be the scapular stabilizing muscles, but larger
groups such as the deltoid and pectoralis major. When putting
a program together for scapular dyskinesis a proper evaluation
should be done to identify all postural distortions,
imbalances, and possible underlying injuries that need to be
taken into consideration and this needs to be done on a case
by case basis.

Conclusions

This study was looking at the peak percentage of muscular
activity from the three main scapular stabilizers; serratus
anterior, upper trapezius, and lower trapezius during the
lawnmower and pushup plus exercises. Along with this data
there was an observation performed for four types of scapular
dyskinesis with one type representing absence of dyskinesis.

35
The subjects included 22 healthy DII baseball players from
California University of Pennsylvania. From this study there
were not any statistically significant findings with the
relationship between peak percentages of muscle activity from
the scapular stabilizing muscles and identifying scapular
dyskinesis.
This study has determined that there is a trend between a
decrease in peak activity of the serratus anterior during the
push-up plus and with those presenting with scapular
dyskinesis. There is also a trend of those presenting with
type one and two scapular dyskinesis to have a decrease of
peak activity of the lower trapezius during the lawnmower
exercise. During the push-up plus it was shown that from the
dyskinesis group, type three had the lowest lower trapezius
peak activity. This relationship has only been supported by
descriptive mean statistics using the peak muscle activity for
each muscle during both exercises and comparing them by
dyskinesis type one through four.
Even though significant results were not present there is
still a known link between scapular movement and arm function,
especially in the overhead athlete that has been made from
previous research.7,12,13 This relationship is called the kinetic
chain and if there is an alteration in the biomechanics of how
one part moves we can expect to see changes along the chain.

36
Although some of the literature states that there is a
connection between scapular dyskinesis and shoulder
pathologies there is also literature stating that there is not
a relationship.7,11 With conflicting literature it is hard to
come to a concrete conclusion, but it does mean that there is
not enough evidence to throw out scapular strengthening
programs all together.
From this study it has been shown that there could be a
relationship between the three prime scapular stabilizing
muscles; upper trapezius, lower trapezius, and serratus
anterior with identifying types of scapular dyskinesis. This
means that when an athlete presents with scapular dyskinesis
we should put them on a program to strengthen the entire
surrounding structures. If a stronger relationship can be
found between types of dyskinesis and either a decrease or
increase in muscle activity we could specify those programs
for each athlete. Not only would we take into account
individual considerations like history and sport, but we could
specify confidently which muscles are underactive or
overactive and why. When that relationship is established we
can then create programs specifically to activate or avoid
which ever muscle groups are involved with the type of
dyskinesis the athlete is presenting with. We now know that
there could be a relationship between muscular activity of the

37
scapular stabilizing muscles and those imbalances correlating
with different types of scapular dyskinesis.

Recommendations

Assessing the relationship between scapular posture and
various shoulder injuries can help reveal information on how
to correct the abnormalities and establish full function once
again. If this study were to be done again the inclusion of
many types of athletes from different sports would help get a
better idea of if the overhead athlete could have altered
muscular patterns from the sports demands which could cause an
imbalance resulting in scapular dyskinesis. Literature has
stated that there has been no significant difference found
between genders and scapular dyskinesis presentation so
including females in this study would probably not have an
effect on the outcome.12 There could be a relationship across
sports and their muscular patterns with previous shoulder
injuries or even scapular posture. Further research into
scapular posture possibly leading to shoulder injuries needs
to be done to help us better understand if there is a
correlation between the two.
Further research into the relationship between the
observation of scapular dyskinesis and activity of the

38
scapular stabilizers needs to be done. This study could be
done again looking at the total time of muscular activity or
peak activity at a given movement during exercise. There is
evidence that there could be a relationship established, there
just needs to be more research done in order to make a
concrete statement that there definitely is a correlation.
Including different exercises which have been shown to
activate the scapular stabilizing muscles could lead to more
findings, and even the inclusion of other scapular stabilizing
muscles would most likely result in additional supporting
information.
If this study were to be done again it would be a good
idea to restrict activity of the subjects before testing.
Recent literature has stated that muscle activity prior to
observing for scapular dyskinesis can lead to adjustments and
make it more difficult to correctly identify the types of
dyskinesis.9 For this study it was difficult to control the
subject‟s activity prior to testing because an entire day was
blocked off with many subjects reporting throughout the day.
Requesting the subjects to avoid physical activity for a whole
day while in season is not practical, many came in for testing
after lifting which could have affected the results and why
there were so many who presented without scapular dyskinesis.
A better way to do this would have been to have many days with

39
just a couple hours of testing prior to practice or in the
morning to ensure that physical activity is minimized before
testing. This was not an option for this study because of time
restraints and schedule changes with the baseball team. It
would be interesting to see what the results would be with
many testing days and the physical activity variable minimized
prior to the subjects undergoing testing.
This study only required the subject to report for one
day and all testing was done. It would be interesting to do
repeated testing to see if results would change overtime; this
would also allow the subjects to become used to the testing
procedures and exercises involved. With this study it took
awhile for the researcher to explain and show the exercises
well enough for the subject to completely understand, and even
then there were a few times the exercises had to be redone. It
might have helped to have a short video of the exercises to be
performed and how to do them properly, the subjects could have
watched this before completing the exercises which might have
helped them understand what was being asked of them.

40
REFERENCES
1.

Dome D, Kibler W. (2006). Evaluation and management of
scapulothoracic disorders. Curr Op Orthop, 17,321-324.

2.

Poppen N, Walker P. (1976). Normal and abnormal motion of
the shoulder. J Bone Joint Surg, 58-A,195-201.

3.

Mazoue C, Andrews J. (2004). Injuries to the shoulder in
athletes. South Med J, 97(8), 748-754.

4.

Kibler W, McMullen J.(2003). Scapular dyskinesis and its
relation to shoulder pain. J Am Academy Orthop Surg,
11(2), 142-151.

5.

Kibler W, Sciascia A, Uhl T, Tambay N, Cunningham T.
(2008). Electromyographic analysis of specific exercises
for scapular control in early phases of shoulder
rehabilitation. Am J Sports Med, 36(9), 1789-1798.

6.

Manske R. (2006). Electromyographically assessed
exercises for the scapular muscles. Athl Ther Today,
11(5), 19-23

7.

Kibler, W. (2006). Scapular involvement in impingement:
signs and symptoms. AAOS Instructional Course Lectures,
55, 35-43.

8.

Borich M, Bright J, Lorello D, Cieminski C, Buisman T,
Ludewig P. (2006). Scapular angular positioning at end
range internal rotation in cases of glenohumeral internal
rotation deficit. J Orthop Sports Phys Ther, 36(12), 926934.

9.

McClure P, Tate A, Kareha S, Irwin D, Zlupko E. (2009). A
clinical method for identifying scapular dyskinesis, part
1: reliability. J Athl Training, 44(2), 160-164.

10.

Ekstom R, Bifulco K, Lopau C, Andersen C, Gough J.
(2004). Comparing the function of the upper and lower
parts of the serratus anterior muscle using surface
electromyography. J Orthop Sports Phys Ther, 34(5), 235243.

11.

Tate A, McClure P, Kareha S, Irwin D, Barbe M. (2009). A
clinical method for identifying scapular dyskinesis, part
2: validity. J Athl Training, 44(2), 165-173.

41

12.

Oyama S, Myers J, Wassinger C, Ricci R, Lephart S.
(2008). Asymmetric resting scapular posture in healthy
overhead athletes. J Athl Training, 43(6), 565-570.

13.

Meyer K, Saether E, Solney E, Shebeck M, Paddock K,
Ludewig P. (2008). Three-dimensional scapular kinematics
during the throwing motion. J App Biom, 24, 24-34.

42

APPENDICES

43

APPENDIX A
Review of Literature

44

Introduction
The primary purpose of this study is to examine the
relationship between types of scapular dyskinesis and activity
of scapular stabilizing muscles. Sports requiring repetitive
overhead motion such as baseball, softball, swimming,
volleyball, and tennis are identified as at-risk populations
for the development of subacromial shoulder impingement
secondary to repetitive placement of the shoulder into
vulnerable positions as well as high forces and loads.1 This
impingement causes a decrease in available space for the
supraspinatus.2

Many past research articles have shown there

is a strong relationship between scapular dyskinesis and
impingement.3-16 This is because the subacromial and
coracohumeral spaces decrease with active humeral elevation,
which can create shoulder-impingement symptoms.2,4,12-16 The
resulting kinematic changes from impingement and altered
scapular movement have been linked with a decrease in serratus
anterior muscle activity, and an increase in upper trapezius
muscle activity, or an imbalance of forces between the upper
and lower parts of the trapezius muscle.9,13,15,17
There is existing evidence supporting scapular dyskinesis
presenting as loss of control in external rotation and
translation of scapular upward rotation leading to

45
supraspinatus inactivation with shoulder impingement.1,3,12-14
Research supports that scapular dyskinesis is found in as many
as 68% of patients with rotator cuff abnormalities, 94% with
labral tears, and 100% with glenohumeral instability.8
Scapular dyskinesis has been identified in subjects
through various methods in the clinic, including postural
asymmetries like scoliosis, muscle atrophy, bony contour,
excessive scapular winging, and inferior angle
prominence.10,14,15,18 Overhead athletes will usually present with
slight bilateral differences when measuring scapular
movement.1,12,15 These differences are caused by the common
finding of the dominant shoulder being positioned lower than
the nondominant shoulder. With overhead athletes this
difference between dominant and nondominant is accentuated by
the repetitive and forceful stretching of the ligaments, joint
capsule, and muscles within the dominant shoulder, making it
even noticeably lower.12,15 By finding how certain scapular
abnormal movements can possibly put an athlete at greater risk
for injury, there should be a way to intervene and correct
those movements before injury occurs.19

The Anatomy of the Scapula
The scapula is often referred to as the shoulder blade.
It lays on the posteriolateral aspect of thoracic ribs 2-7.15

46
Bony landmarks anteriorly include the acromion process,
subscapular fossa, and the coracoid process. The acromion is
an important landmark of the shoulder anatomy because it is
where shoulder impingement is most likely to occur.3,7-10,13-15
Impingement often involves the supraspinatus, infraspinatus,
and teres minor tendons, which all pass underneath the
acromion.2,20 The impingement can be primary or secondary.
Primary impingement would be caused by a beaking of the
acromion process, with three stages of severity. Secondary
impingement is caused by overuse, usually overhead motions,
where the rotator cuff muscles become irritated and inflamed,
putting pressure underneath the acromion process.14,20
Along with the three rotator cuff muscles, there is also
a subacromial (also called subdeltoid) bursa located between
the acromion, coracoacromial ligament and deltoid superiorly
and the supraspinatus tendon and joint capsule of the
glenohumeral joint inferiorly.20 This bursa prevents the
tendons from rubbing against the bone, ligaments, or other
tendons, and creates a smooth area where skin moves over bone
without much underneath.2,20
The coracoid process provides an attachment site for the
pectoralis minor and short head of the biceps tendon. The
other landmark, the subscapular fossa, is the site of muscular
attachment for the subscapularis. The subscapularis is part of

47
the rotator cuff, but the only one that will actively pull the
arm into internal rotation of the humerus because of the
attachment onto the lesser tuberosity of the humerus.20 The
teres minor and infraspinatus muscles will create external
rotation with their attachment onto the greater tuberosity of
the humerus, along with other movements which will be
discussed later.20,22
The fossae of the scapula are areas that contain muscle.
Within the supraspinous fossa lays the supraspinatus muscle;
the infraspinous fossa holds the infraspinatus muscle. As
mentioned previously, these both are rotator cuff muscles.20,22
The rotator cuff is considered a dynamic stabilizer of the
glenohumeral joint, and all rotators except the teres minor
have attachments to the scapula.15,20 There are 17 muscles which
attach or insert onto the scapula.4 All of the muscles work
with the rotator cuff, which stabilizes humeral movement, and
together they create coordinated movements of the glenohumeral
articulation by way of force couples.2,4,16,22 This is a good
indication that the scapula plays an important role in the
functional movements of the shoulder. The supraspinatus has a
primary role of stabilizing the humerus superiorly, but also
performs abduction of the humerus.20,22 The infraspinatus is
entirely an external rotator.20,22 The spine of the scapula
serves as a separator between these muscles.20

48

The Glenohumeral Joint
The glenohumeral joint has the most degrees of freedom
compared to any other joint in the body.20 With this freedom
comes a sacrifice, a decrease in stability.2 The muscles
surrounding the glenohumeral joint consist of the rotator cuff
muscles; supraspinatus, infraspinatus, teres minor, and
subscapularis. These muscles are the dynamic stabilizers of
the joint; they help to hold the humeral head in the glenoid
fossa by active contraction.2 A static stabilizer of the
glenohumeral joint is the glenoid labrum.2 This labrum is a
fibrocartilagenous rim that widens and thickens the glenoid
fossa.2,15,20 The glenoid fossa is not large enough to securely
hold the humeral head in place; the labrum doubles the surface
area allowing more stability.15,20
The scapula influences the glenohumeral joint in many
ways. Research debates on whether dyskinesis can lead to, or
is a product of shoulder injury.24,25 In one study by Kibler et
al. it was shown that 100% of the participants with shoulder
pathologies, specifically instability, were also suffering
from scapular dyskinesis.3 When the arm is elevated in an
overhead motion horizontally, the humerus is controlling most
of the lower degrees of movement, but when the arm reaches 82°
of flexion, the scapula dominates the upper levels of

49
elevation. At 21° the scapula is inactive, at 82° the scapula
has moved 14°, at 139°the scapula moves 48°, with 168° of
glenohumeral abduction the scapula has moved 54°.8 This ratio
of humeral to scapular motion has been shown to be 2:1
throughout the full range of motion.3,8,21 Most of the movement
occurs at the glenohumeral joint during the first 30° of
abduction and the first 60° of flexion at a ratio of 4:1; then
it continues as a 5:4 ratio.21 The scapula is responsible for
upward rotation in order to clear the humerus from contacting
the acromion, along with the supraspinatus which is
responsible for keeping the humeral head stabilized within the
glenohumeral joint. If this upward rotation does not occur, or
if there is insufficient stabilizing musculature control of
the scapula, or weakness of the supraspinatus, the humerus is
unable to clear the acromion and this will lead to
impingement.2-5,13-15 Along with the upward rotation, other
sources have stated that the scapular motions are more complex
than that, involving posterior tilting and external elevation
in order for clearance to happen.8,12,15
Proper position of the scapula is required for correct
transfer of forces from the body through the shoulder to the
hand.26,27 With abnormal scapulohumeral rhythm the shoulder will
not function optimally, and injury may result.26 Scapular
dyskinesis affects the scapulohumeral rhythm negatively. With

50
abnormal scapular motion, the forces upon the glenohumeral and
elbow joints change.15,26 This is important for clinicians, who
are working with overhead athletes, specifically pitchers and
throwing athletes, because there are already so many unnatural
torque forces that an increase can severely injure the
athlete. Baseball pitchers in particular experience huge
torque forces, with a maximum rotational velocity approaching
7,000° per second, possibly the fastest human motion in all
sports.15

The Scapulothoracic Joint
The scapula and its translational movement over the
thoracic ribs create the scapulothoracic joint.7,28 This is not
a true joint but it functions by translation and rotational
movements over the thoracic ribs.29 Without the scapula, the
glenohumeral joint would be severely compromised and unable to
move properly.1-29
Normal scapular movement consists of protraction,
retraction, downward rotation, upward rotation, posterior
tipping, anterior tipping, medial rotation, and lateral
rotation.1,12,15,29 The upward/downward rotation occurs around
the horizontal axis perpendicular to the plane of the scapula,
the internal/external rotation occurs around a vertical axis
through the plane of the scapula, and anterior/posterior

51
tipping occurs around a horizontal axis in the plane of the
scapula.3
Kibler has defined four roles for the scapula:
providing a site for muscle attachment, providing stability
for the glenohumeral joint, providing retraction and
protraction of the shoulder girdle around the thoracic wall
during motion of the upper extremity, and elevation of the
acromion process on the scapula.4 Along with the biomechanical
roles of the scapula, it also serves as an attachment and
insertion site for seventeen muscles.4 The rotator cuff, along
with all of the attached muscles, works in coordination to
control glenohumeral articulation.19,20 These muscles create
force couples to stabilize and move the scapula and
arm.15,16,19,26 The scapula acts as a stabilizing base from which
the muscles can work.4 It has been shown that with shoulder
injuries there is a change in muscle activation patterns and
strength.9,27 Also, abnormal glenohumeral articulation can be a
major factor in shoulder injuries, and should be given more
attention clinically in order to avoid untimely injuries and
rehabilitation.7,8,30

Scapular Dyskinesis
The most common definition found for scapular dyskinesis
involves an alteration in the normal position or motion of the

52
scapula during coupled scapulohumeral movements.3,24,25 Scapular
dyskinesis is also thought of as abnormal movements of the
scapula, presenting bilaterally, or unilaterally.12 Many
overhead athletes will have bilateral differences between
scapular movements because of the overuse of their dominant
arm.12 As clinicians it is important to know the likelihood of
scapular dyskinesis affecting shoulder injuries.
Scapular dyskinesis has been found to be related to
shoulder impingement.1-3,12-15 In external impingement, the
decreased posterior tilt and upward rotation of the scapula
prevents elevation of the acromion, which places increased
pressure on the rotator cuff and decreases subacromial space
during arm elevation.3 With internal impingement, massive
scapular internal rotation and protraction of the dyskinetic
position creates glenoid anterior tilting with increased
mechanical movement of the humerus and supraspinatus against
the glenoid and labrum, which can result in labral tears, and
also „dead arm‟ syndrome.3
Scapular dyskinesis can be brought on by either proximal
or distal factors, both affecting the movement pattern.
Proximal factors include postural alterations of the spine,
hip or trunk weakness or inflexibility, scapular stabilizing
muscle weakness or neurological lesions in the spinal cord or
peripheral nerves.3 Distal factors are usually the result of

53
muscle inhibition due to injury such as labral tear,
instability, rotator cuff tears, impingement, or soft tissue
inflexibilities.3 Muscle inhibition appears to be a
nonspecific response to a painful condition of the shoulder
rather than a response to specific shoulder pathology.25,27
Inhibition results in a loss of force generation as well as an
alteration in muscle firing and muscle coupling about the
shoulder.29,11 These distal anatomical injuries can be the cause
of altered muscle imbalances or activation patterns; in order
to correct this cycle, surgery is usually necessary.3 The
proximal causes are directly related to the scapula, while the
distal causes are dealing mostly with the shoulder.3
A causative factor of scapular dyskinesis that is
becoming more recognized is glenohumeral internal rotation
deficit (GIRD). This is defined as a bilateral asymmetry of
greater than 25° of shoulder range of motion.30 If an athlete
presents with 90° of humeral internal rotation on one side,
and only 45° on the other side, they would be a candidate for
identifying GIRD. Posterior capsule tightness can be a cause
of GIRD and can create abnormal scapular movements during the
“windup” of a throw. When the humerus is flexed forward,
horizontally adducted, and internally rotated, the tight
capsule and muscles pull the scapula into a position that is
protracted, internally rotated, and anteriorly tilted.30 The

54
significance of this finding is that many overhead athletes,
specifically throwers, will develop this posterior tightness.
The posterior capsule and muscles can become overworked from
the stress of repeatedly decelerating the arm, and therefore
tightening and creating altered kinematics within the shoulder
and possibly putting that athlete at a greater risk of
injury.15,30

Biomechanical Factors
There are many different sports which use overhead
athletes; softball, baseball, swimming, volleyball, tennis,
shot put, and javelin. While there are different biomechanical
forces occurring with each movement, most overhead throwing
athletes will present with an increase in external rotation
and a decrease with internal rotation when positioned with the
shoulder and elbow at 90°-90°.15 This can be explained by the
rotation of the humerus about its central contact point on the
glenoid. With external rotation, the inferior glenohumeral
ligament tightens, and if the posterior band is shortened from
overuse, there will be a shift of the glenohumeral contact
point posterosuperiorly, during combined abduction and
external rotation.3 Because the arc of motion of the greater
tuberosity has now shifted posterosuperiorly a greater degree
of external rotation can be found.3,15,26

55
Baseball pitching has been known to have the greatest
amount of torque put on the elbow and shoulder while
performing. Consequently, there is a vast amount of research
describing the sequence of events. There are many factors to
take into consideration with all overhead athletes. One is the
fact that the scapula and glenohumeral joint are closely
related. The scapular stabilizer muscles (rhomboids, serratus
anterior, middle and lower trapezius) are attached along the
inferior, superior, and medial borders, allowing the scapula
to move correctly in all of its motions.11,15,20 The lower fibers
of the trapezius are especially important in normal scapular
kinematics because of their mechanical role in the translation
of the instant center or rotation.11,15 Weakness of the
scapulothoracic muscles results in poor scapular stabilization
and excessive movement of the scapula, causing abnormal motion
of the humeral head relative to the glenoid fossa, and in turn
leading to possible inflammation of the soft tissue.3,15,29 The
scapula acts as a link in the kinetic chain, and is an
essential component for the proximal-to-distal transfer of
velocity, energy, and forces that accompany overhead actions.26
The scapula acts to collect and transfer forces to the upper
extremity, and if insufficient constraint is provided by
structures surrounding the scapula, such as the muscles,
ligaments, joint capsule and bony structure,

failure occurs

56
in the kinetic chain.15,26,29 Altered scapular position alters
the scapulohumeral rhythm and can change the force on the
glenohumeral and elbow joints, decreasing the efficiency of
the rotator cuff, which is often associated with many common
shoulder problems, including impingement, instability, and
labral injuries.4,8,15,21,26
Bony posture must also be taken into consideration when
evaluating an athlete or patient. Thoracic kyphosis or
cervical lordosis may result in excessive scapular
protraction, while acromial depression can lead to impingement
of the rotator cuff tendons.8 Clavicular malunions may cause
significant shortening of the strut that maintains appropriate
scapular positioning on the thoracic wall. Acromioclavicular
instability will also affect the loss of communication since
the clavicle makes direct contact with the scapula at the
acromioclavicular joint such that any alteration would also
influence the scapular patterns.8,15,29 Lower grade instability
or arthrosis of the acromioclavicular joint may cause changes
in the instant center of rotation of the acromioclavicular
joint and alter scapular mechanics. Higher grade instability
will produce further protraction of the scapula and acromial
depression, leading to loss of strength and impingement of the
rotator cuff.8 Acromioclavicular joint instability may result
in a new abnormal motion of the joint with inferior and medial

57
translation of the acromion beneath the clavicle causing
further dysfunction of the scapulohumeral rhythm.8,15
Scapular motion is a 3-dimensional movement that involves
a combination of translation and rotation, which act together
to allow efficient humeral motion.15 During humeral elevation
in the scapular plane, the scapula provides a stable base for
the upper extremity so that the rotator cuff muscles,
specifically the supraspinatus, effectively compress the
humeral head into the glenoid thereby decreasing the amount of
translation between the glenoid and humeral head. The rotator
cuff can lessen the risk of soft-tissue impingement under the
coracoacromial arch.3,23 Internal rotation has been
demonstrated to produce greater scapular upward rotation than
any other glenohumeral rotation.15 If an athlete is displaying
an increased amount of scapular upward rotation at humeral
elevation with glenohumeral internal rotation, they could be
at greater risk for subacromial and subcoracoid space
impingement.6,15 Compression of the rotator cuff tendons in the
subacromial space alters the biomechanics of the glenohumeral
joint causing weakness and reduced range of motion.7,15 In
previous studies, subjects with impingement have been shown to
have different scapular kinematics when compared with a
control group, showing anterior tilting and decreased
posterior tipping of the scapula in the scapular-plane

58
elevation.3,14,21 Those subjects with shoulder impingement have
also been shown to have excessive scapular upward rotation
with simple arm movements.21
While scapular upward rotation is necessary to avoid
impingement with humeral elevation, excessive amounts can have
negative functional effects.8 Determining excessive amounts
can be done by bilateral comparisons of the scapulas, which
should move in unison. Another abnormal movement is a
protracted position of the scapula, which has been shown to be
related to shoulder subluxations.8 The inability to fully
retract the scapula prevents the scapula from providing a
stable base for cocking of the arm during throwing or
elevation of the arm during forward flexion.15 Loss of scapular
retraction leads to excessive arm extension posterior to the
plane of the scapula during the throwing motion. This causes
increased strain on the anterior capsule and posterior
superior labrum.12
When it comes to abduction of the arm, it has been said
that the “true abduction” is not in the frontal plane, but in
the “plane of the scapula”. This is because the scapula is
angled at 30° to 45° anterior to the coronal plane. Within the
scapular plan, the inferior part of the glenohumeral capsule
is not twisted, while the deltoid and supraspinatus are also
optimally aligned for elevation of the arm.26

59
All of the joints of the shoulder girdle move
simultaneously, but with abduction the glenohumeral joint
moves twice as much as the scapulothoracic joint. An analysis
of abduction in the scapular plane found a ratio of 3:2
between glenohumeral and scapulothoracic motion. After 30° of
abduction the ratio jumps to 5:4 for glenohumeral-toscapulothoracic movement. This means that for a given arc of
movement, the humerus moves 5° on the glenoid, while the
scapula moves 4° on the thorax. The reason for the difference
after 30° of abduction is because from 0°-30° most of the
movement is glenohumeral and upward, while there is a lowering
of the scapulothoracic joint for the motion of 30° and
upward.21

Electromyographic Activity and Scapular Movements
In order to get a better understanding of the exercises
which activate the scapular muscles, researchers‟ measure
electromyographic (EMG) activation. The measurement of muscle
activity is found by placing surface electrodes over the
specific muscle fibers.31 The exact placement is determined by
resistive exercises to attempt to generate 100% muscle
contraction or maximum voluntary isometric contraction.11 Then
the subject is asked to perform various movements, so that
whichever movements activate the muscle the most can be

60
determined as an effective activation movement for that
particular muscle. Not all exercises will activate 100%, but
if the exercise is able to generate at least 20%, it is
considered a moderate strength gain.11,32
Muscle activity surrounding the scapula is important in
order for the scapula to maintain its stable base of operation
at the scapulothoracic joint.15,27 If the muscles are not
functioning properly because of abnormal motion or asynchrony
of firing patterns, overhead athletes are at greater risk for
injuries such as subacromial impingement and other overuse
syndromes.3-11,15,16,27
The serratus anterior, trapezius, rhomboid, and
pectoralis minor are scapular stabilizers that are often
monitored during EMG research.11,15-17,22,26,27 The serratus
anterior forms a force couple relationship with the trapezius
muscle to produce upward rotation of the scapula.11,15,26 This
movement is critical for overhead athletes in order to avoid
impingement.15 In the absence of proper activation of the
trapezius and serratus anterior, an individual may present
with scapular winging.11,18,27 A classic case of scapular winging
occurs with palsy to the long thoracic nerve, which innervates
the serratus anterior.18

61
Function of the Scapula and Glenohumeral Joint
The relationship between the scapula and how the shoulder
functions has been established. Scapulothoracic dysfunction
has been increasingly recognized as a contributor to many
common shoulder disorders.3,7,8,16,18,26 In order to avoid injuries
to the shoulder complex during overhead motions there must be
an understanding of why and how the symptoms begin to develop.
The close relationship between scapular upward rotation and
positions of the greater and lesser tuberosities should be
considered because of their relationship to glenohumeral
rotation.8,15,26 Glenohumeral rotation is an important factor in
overhead sports and can affect performance negatively if not
able to achieve full range of motion.15 If the humeral-and
scapular-control muscles become fatigued, a greater overload
and muscle weakness and muscle imbalance will occur in the
humeral force couples.26 These force couples create an abnormal
amount of compression and shear stress at the glenohumeral
joint.15,26
The acronym SICK (scapular malposition, inferior medial
border prominence, coracoid pain and malposition, and
dyskinesis) has been created by Burkhart et al, who believes
with this theory that asymmetry of the scapula is abnormal.12
This acronym describes the asymmetry of the scapula commonly
seen in overhead athletes with shoulder abnormalities. SICK is

62
based upon the theory that asymmetry is a sign of the
underlying alteration in the muscle activation associated with
various shoulder conditions. A demonstration of this
abnormality has not been shown in previous research because of
the inability to describe scapular posture 3-dimensionally.12
There has been support for the statement that an injured
overhead athlete may display more asymmetry than healthy
overhead athletes, and there may be a pathologic threshold for
scapular posture asymmetry at which asymmetry becomes a
problem.12,15,29
An abnormality seen in the overhead throwing population
is the glenohumeral internal rotation deficit (GIRD).3 This
condition is presumed to develop secondary to posterior
capsule tightness.3,15,26,27,29 The percent deficit of internal
rotation can be found by dividing the difference between the
dominant arm and nondominant arm internal rotation values and
multiplying by 100 [((ND-D)/ND)x100].1 Glenohumeral internal
rotation at 90° of humeral elevation significantly tightens
the posterior capsule as well as bringing the supraspinatus in
closer contact with the acromion.3,30 When looking at scapular
movement with GIRD it has been consistently found that there
is an increased anterior tilt of the scapula in those
individuals presenting with GIRD.1,4,7,8

63
When treating scapulothoracic disorders, the proximal and
distal causative factors must be taken into consideration.
Once the complete and accurate diagnosis of all factors
causing or contributing to scapular and shoulder problems are
established, scapular rehabilitation may be initiated.1
Surgery might be an option for some of the issues like nonunion of the clavicle or acromioclavicular joint.18 The
individual who presents with these symptoms will need
rehabilitation back into normal functioning. The starting
point for a rehabilitation program would be restoration of
flexibility.31 Stretching of the posterior capsule to regain
glenohumeral internal rotation can be accomplished through
„sleeper stretches‟.30 The patient can do this stretch by
laying on their side with the affected arm abducted, and the
unaffected arm performing the internal rotation stretch.31 A
passive stretch for coracoid based tightness is performed by
passive horizontal extension of the shoulders as in an open
book position.31 With this stretch it is important to keep the
arms below 90° abduction to avoid thoracic outlet symptoms.
General flexibility of the trunk has also been shown to help
restore flexibility to the scapulothoracic joint.12
Many protocols begin with strengthening the surrounding
scapular muscles, otherwise known as periscapular. The goal of
this phase is to restore the correct position of external

64
rotation and posterior tilt of the scapula, or retraction.16,27
The periscapular muscles are often weak from disuse atrophy
and inhibition due to pain. Initial strengthening should be
performed with exercises that take advantage of the
facilitation of periscapular activation through synergistic
proximal trunk and hip muscle activation.11,26,31 These exercises
should be performed in a closed chain fashion to avoid
straining the distal injured or repaired structures.31 When
starting a scapular muscle rehabilitation program scaption,
rowing, push-up with a plus, and press-up exercises are common
and often referred to as the Moseley scapular core exercises.31

Summary

The literature demonstrates that the scapula has a direct
effect on the function of the glenohumeral joint. Muscles that
make up the scapular stabilizers need to fire correctly in
order for force to be correctly transferred from the torso to
the glenohumeral joint. If there is an imbalance of muscle
activation scapular dyskinesis can result. Without efficient
transfer of forces the glenohumeral joint may suffer an
injury. There is evidence that certain shoulder injuries,
especially impingement, can also be correlated with scapular
dyskinesis.

65
Different types of scapular dyskinesis are identified by
various abnormal motions of the scapula during overhead arm
movement. A reason for these variations of scapular dyskinesis
is from an alteration in muscle firing. By identifying which
muscles are associated with a certain type of scapular
dyskinesis, a specific protocol for exercises that effectively
activate the correct muscle can be developed. This means that
for certain types of scapular dyskinesis, a specific protocol
will be given instead of a general scapular stabilizer
strengthening program. This will help the athletes because
depending of the type of scapular dyskinesis a muscle group
could be overactive or not firing at all. By giving them a
general protocol it may worsen their symptoms by possibly not
working the muscles that are not firing, but perhaps
activating the already overactive muscles.

66

APPENDIX B
The Problem

67
THE PROBLEM

Sports requiring repetitive overhead motion such as
baseball, softball, swimming, volleyball, and tennis are
identified as at-risk populations for the development of
subacromial shoulder impingement secondary to repetitive
placement of the shoulder into vulnerable positions as well as
high forces and loads.8 This impingement causes a decrease in
available space for the supraspinatus.20

Past research has

demonstrated a strong relationship between scapular dyskinesis
and impingement.1,2,3,4,5,6,22 This is because the subacromial and
coracohumeral spaces decrease with active humeral elevation,
which can create shoulder-impingement symptoms.2,8,19 The
resulting kinematic changes from impingement and altered
scapular movement has been linked with a decrease in serratus
anterior muscle activity, an increase in upper trapezius
muscle activity, or an imbalance of forces between the upper
and lower parts of the trapezius muscle.22

The scapular

stabilizer muscles (rhomboids, serratus anterior, middle and
lower trapezius) are attached along the inferior, superior,
and medial borders, allowing the scapula to move correctly in
all of its motions.4,5 The lower fibers of the trapezius are
especially important in normal scapular kinematics because of
their mechanical role in the translation of the instant center

68
or rotation.5,6 In one study the serratus anterior was shown to
have decreased activity throughout all movements analyzed in
those with shoulder impingment.22 The purpose of this study was
to examine the relationship between a decrease in activity
from the scapular stabilizing muscles of the serratus
anterior, lower trapezius, and upper trapezius during
exercises and observe for three types of scapular dyskinesis.

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

Maximum Voluntary Isometric Contraction (MVIC):
normalized the data collected by the EMG machine. Served
as the reference value to compare the peak muscle
activity levels which occurred during the movements.

2)

Muscle Activation – The level of recruitment of muscle as
sent via the efferent nerve pathway from the brain
measured by EMG.

3)

Strengthening – 20%-30% of MVIC is considered to be
effective for moderate muscle strengthening.19

69
Basic Assumptions
The following were basic assumptions of this study:
1)

There was no evidence that the volunteers would respond
differently than random subjects.

2)

The subjects answered truthfully on the demographic
sheet.

3)

The equipment was working correctly and properly
calibrated.

4)

The subjects were overhead athletes with no prior history
of upper extremity injury within the last six months, and
performed to the best of their ability.

Limitations of the Study
The following were possible limitations of the study:
1)

The equipment that was available for this study may not
have been the newest version available. This will not
affect the study because the equipment that was used was
still reliable and valid.

2)

The participants may not have had any experience in
scapular stabilization strengthening.

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Delimitations of the Study
The following were the delimitations of the study:
1)

The subjects were college students ages 18-30, from
California University of Pennsylvania..

2)

Pertained to an injury free populace.

3)

Active individuals.

Significance of the Study
Scapular stabilization and activation of the surrounding
muscles can help prevent imbalances that can lead to shoulder
injuries. Programs involving scapular stabilizer strengthening
are seen in the athletic training room, physical therapy
clinic and weight room.
This study investigated the difference between decreases
in scapular stabilizers and identifying scapular dyskinesis.
If there is a relationship between the two, then the support
for scapular stabilization programs will grow. Additionally,
evidence of this relationship will help athletic trainers
understand how to prevent dyskinesis and how to treat it when
found. When identifying what type of scapular dyskinesis the
athlete presents with, the athletic trainer will be better
able to understand what muscles are active and what muscles
need to be strengthened in order to correct the imbalance.
Through this study a more specific protocol for those with

71
scapular dyskinesis can be developed in order to correct the
dyskinesis and prevent serious overuse injuries from
occurring. From this study finding a trend with a lower mean
average of peak muscle activity from specific scapular
stabilizers during two exercises and presenting with a certain
type of scapular dyskinesis there can be further research done
to determine the relationship and specific protocol exercises
to strengthen those muscles.

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APPENDIX C
Additional Methods

73

APPENDIX C1
Informed Consent Form

74

Informed Consent Form
1. Jenna Sherman, who is a Graduate Athletic Training Student at California University of
Pennsylvania, has requested my participation in a research study at California University of
Pennsylvania. The title of the research is Relationship Between the Observation of Types of
Scapular Dyskinesis and Peak Muscle Activity of the Scapular Stabilizing Muscles.

2. I have been informed that the purpose of this study is to better understand the types of
scapular dyskinesis and why there are different types. With this relationship there will be
evidence that protocols for rehabilitation of scapular dyskinesis can be made specific to the
type of dyskinesis instead of general scapular strengthening programs. I understand that I
must be 18 years of age or older to participate. I understand that I have been asked to
participate along with overhead athletes from baseball, softball, volleyball and swimming. I
have no previous head injury, or upper body extremity injury within the last 6 months that
might put me at risk for further injury. I also do not have any neurovascular disorders which
could interfere with balance and performance of the tasks asked of me. I am physically
active, as defined as participating in moderate to intense exercise at least 3 times a week. I
am cleared for full participation in my sport by a physician for this current competitive year
2009-2010.
3. I have been invited to participate in this research project. My participation is voluntary
and I can choose to discontinue my participation at any time without penalty or loss of
benefits. My participation will involve filling out an injury history and demographic form
before the study begins. I will be first asked to perform movements to identify types of
scapular dyskinesis. These movements include horizontal arm abduction with dumbbell
weights that will be performed along with a metronome with three beats up and three beats
down. These weights will be determined by my body weight, if under 150lb I will use the 3lb
dumbbell, if over 150lb I will use the 5lb dumbbell. The second part of the study involves
electromyographic (EMG) analysis of three scapular stabilizing muscles. This involves
having electrode pads placed on my skin over the muscle bellies. After placement of the
electrodes I will be given an opportunity to warm-up and practice the exercises analyzed
which include the lawnmower exercise and push-up plus. The warm-up involves horizontal
arm movements with medium resistance Therabands® and 15 push-ups. After the warm-up I
will practice the exercises and get used to the metronome of three beats up and three beats
down. The first exercise that will be asked of me is the lawnmower, a multijoint exercise that
has been shown activate the muscles which provide scapular retraction. The second exercise
will be the push-up plus, which is also a multijoint exercise and is a basic push-up with an
extension at the end of pushing the body further up by rounding the shoulders and protracting
the scapulas. Neither one of these exercises will involve resistance.

75
4. I understand there are foreseeable risks or discomforts to me if I agree to participate in the
study. With participation in a research program such as this there is always the potential for
unforeseeable risks as well. Risks with this study are very low because of the use of light
weights and constant monitoring of performance. For this study it is important that all
movements be performed with good technique and form which decreases risk of injury
further. This study does require upper extremity movement which may pose a risk of injury
due to possible aggravation of the shoulder. To minimize these risks the researcher will be
asking me questions about upper extremity injuries prior to the start of the study. The
researcher will also stand by closely during the balance testing in case I need help or begin to
lose form.
5. I understand that, in case of injury, I can expect to receive treatment or care in Hamer
Hall’s Athletic Training Facility. This treatment will be provided by the researcher, Jenna
Sherman, under the supervision of the CalU athletic training faculty, all of which can
administer emergency care. Additional services needed for prolonged care will be referred to
the attending staff at the Downey Garofola Health Services located on campus.
6. There are no feasible alternative procedures available for this study.
7. I understand that the possible benefits of my participation in the research are going to help
athletic trainers better understand scapular dyskinesis and create proper rehabilitation
protocols. This study can help athletic trainers identify the different types of dyskinesis as
well as making them aware that general scapular strengthening programs could potentially be
treating the wrong muscles. Through my participation, an understanding of creating specific
programs for each type of dyskinesis and strengthening the inactive muscles while treating
the overactive muscles can be made.
8. I understand that the results of the research study may be published but my name or
identity will not be revealed. Only aggregate data will be reported. In order to maintain
confidentially of my records, Jenna Sherman will maintain all documents in a secure location
on campus and password protect all electronic files so that only the student researcher and
research advisor can access the data. Each subject will be given a specific subject number to
represent his or her name so as to protect the anonymity of each subject.
9. I have been informed that I will not be compensated for my participation.
10. I have been informed that any questions I have concerning the research study or my
participation in it, before or after my consent, will be answered by:
Jenna Sherman, ATC
STUDENT/PRIMARY RESEARCHER
She1570@calu.edu
269-788-4168
Edwin Zuchelkowski, Ph.D.
RESEARCH ADVISOR

76
zuchelkowki@cup.edu
724-938-4202
11. I understand that written responses may be used in quotations for publication but my
identity will remain anonymous.
12. I have read the above information and am electing to participate in this study. The nature,
demands, risks, and benefits of the project have been explained to me. I knowingly assume
the risks involved, and understand that I may withdraw my consent and discontinue
participation at any time without penalty or loss of benefit to myself. In signing this consent
form, I am not waiving any legal claims, rights, or remedies. A copy of this consent form will
be given to me upon request.
13. This study has been approved by the California University of Pennsylvania Institutional
Review Board.
14. The IRB approval dates for this project are from: 09/01/2009 to May/07/2009.

Subject's signature:___________________________________
Date:____________________
Witness signature:___________________________________ Date:____________________

77

APPENDIX C2
Institutional Review Board –
California University of Pennsylvania

78

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83

84

85

86

87

88
Dear Jenna,
Please consider this email as official notification that your proposal titled
“Relationship Between Muscle Activity of Scapular Stabilizers and Identifying
Types of Scapular Dyskinesis” (Proposal #09-039) has been approved by the
California University of Pennsylvania Institutional Review Board.
The effective date of the approval is 01-28-2010 and the expiration date is 0128-2011. These dates must appear on the consent form .
Please note that Federal Policy requires that you notify the IRB promptly regarding
any of the following:
(1) Any additions or changes in procedures you might wish for your study
(additions or changes must be approved by the IRB before they are
implemented)
(2) Any events that affect the safety or well-being of subjects
(3) Any modifications of your study or other responses that are necessitated by
any events reported in (2).
(4) To continue your research beyond the approval expiration date of 01-282011 you must file additional information to be considered for continuing
review. Please contact instreviewboard@calu.edu

Please notify the Board when data collection is complete.
Regards,
Christine Gorby
IRB Graduate Assistant

89

Appendix C3
Individual Data Collection Sheet

90
Subject Number:
Right or Left Arm Dominant:
Scapula Dyskinesis Identified:

Yes

No

Type of Dyskinesis Identified:
1 Definition: prominence of the inferior medial scapular
border. This motion is primarily abnormal rotation
around a transverse axis.4
2 Definition: prominence of entire medial border and
represents abnormal rotation around a vertical axis.4
3 Definition: superior translation of the entire scapula
and prominence of the superior medial scapular border.4

91

Appendix C4
Figures and Tables

92
Table 4.
Electrode Placement and MVIC Test Positions for Normalization of EMG
Muscle
Electrode Placement
Position
Upper Trapezius

Electrodes placed 2
cm apart on the upper
back halfway between
C7 spinous process
and the acromion
process.

Subject: shoulders
placed in a shrugged
position.
Examiner: One hand
placed over upper
trapezius between
neck and acromion.
Subject:
Isometrically
shrugged resisting
shoulder depression

Lower Trapezius

Electrodes placed 2
cm apart on an
oblique angle, 5 cm
down from the
scapular spine and
outside the medial
border of the
scapula.

Subject: Prone with
arm passively placed
to 180 degrees of
flexion.
Examiner: One hand
placed on back below
scapula and one hand
placed over distal
humerus above elbow.
Subject:
Isometrically forward
flexed resisting
extension.

Serratus Anterior

Electrode placed 2 cm
apart just below the
axilla at the level
of the inferior angle
of the scapula
(medial to the
latissimus dorsi).

Subject: Arm forward
to 130 degrees.
Examiner: One hand
placed over dorsal
arm and one hand
placed on lateral
scapula for
stability.
Subject:
Isometrically flexed
resisting forward
extension.

MVIC, maximal voluntary isometric muscle contraction; EMG,
electromyography

93
1.

Table 4. Kibler W, Sciascia A, Uhl T, Tambay N,
Cunningham T. (2008). Electromyographic analysis of
specific exercises for scapular control in early
phases of shoulder rehabilitation. The American
Journal of Sports Medicine, 36, 1780-1798

Table 5. Raw Data of 4x2 MANOVA
Descriptive Statistics

peak % UT

exercise

Type

1

1

1.30139343333E0

1.039329004023E0

3

2

5.01883340000E0

6.755330622089E0

3

3

2.20110783333E0

1.965919819141E0

3

4

1.09956941538E0

.833675117549

13

Total

1.81174574545E0

2.656395717140E0

22

1

2.54193343333E0

2.064431971826E0

3

2

.35413568867

.371489342544

3

3

1.16634622733E0

1.292708536360E0

3

4

1.19366872462E0

1.455451507486E0

13

Total

1.25931543036E0

1.464457616325E0

22

1

1.92166343333E0

1.611991161713E0

6

2

2.68648454433E0

4.983655272948E0

6

3

1.68372703033E0

1.592354832468E0

6

4

1.14661907000E0

1.163061390076E0

26

Total

1.53553058791E0

2.138134007268E0

44

1

1.45503228000E0

.723553040803

3

2

2.12551893333E1

3.420198337362E1

3

3

6.40316696667E0

7.049963191293E0

3

2

Total

peak % LT

1

Mean

Std. Deviation

N

94

2

Total

peak % SA

1

2

Total

4

1.01731642174E2

3.443890401816E2

13

Total

6.40841597273E1

2.646977196167E2

22

1

3.76246843333E0

3.709136894435E0

3

2

5.02815706667E0

2.496619582275E0

3

3

3.50672963047E0

4.650295558367E0

3

4

4.42483402492E2

1.558155746655E3

13

Total

2.63144377172E2

1.198338761175E3

22

1

2.60875035667E0

2.703658388613E0

6

2

1.31416732000E1

2.343925091094E1

6

3

4.95494829857E0

5.572046005217E0

6

4

2.72107522333E2

1.119145462503E3

26

Total

1.63614268450E2

8.635186095305E2

44

1

1.666353050000E0

.8739939405493

3

2

3.821263333333E0

5.4010201535001E0

3

3

1.534785224043E4

2.6579590768254E4

3

4

2.925430782031E1

7.8701755727248E1

13

Total

2.110923889642E3

9.8117339094250E3

22

1

1.767297933333E0

.8583322435650

3

2

.776455266667

.7595547580416

3

3

1.991679454249E3

3.4486068715047E3

3

4

3.083764539231E1

7.1998521858698E1

13

Total

2.901617732931E2

1.2707039066799E3

22

1

1.716825491667E0

.7767218422482

6

2

2.298859300000E0

3.8315054091627E0

6

3

8.669765847341E3

1.8462481397503E4

6

4

3.004597660631E1

7.3905165524151E1

26

Total

1.200542831467E3

6.9751184816338E3

44

95
Table 6. Mean peak percentage values for each muscle and
exercise
Peak % UT

Peak %

Peak %

Peak %

Peak %

Peak %

LM

LT LM

SA LM

UT PUP

LT PUP

SA PUP

Mean

3081.89

76.71%

7987.04%

5642.37%

6133.87%

23059.21%

and

(8117.64%)

(84.26%)

(36726.88%)

(15114.56%)

(28466.56%)

(105049.66%)

SD

96

Appendix C5
Demographic Information

97
Demographic Information
Weight in pounds: <150

or

Sport played: _________________
Position played: ______________
Dominant Arm: _________________

Number Assigned:

>150

98
ABSTRACT
Title:

RELATIONSHIP BETWEEN THE OBSERVATION OF TYPES
OF SCAPULAR DYSKINESIS AND PEAK MUSCLE ACTIVITY
OF THE SCAPULAR STABLIZING MUSCLES.

Researcher:

Jenna M. Sherman

Advisor:

Dr. Edwin M. Zuchelkowski

Date:

May 2010

Research Type: Master‟s Thesis
Purpose:

To investigate the relationship between the
peak activity of the three main scapular
stabilizing muscles and identifying types of
scapular dyskinesis.

Problem:

There has been a strong correlation shown
between scapular dyskinesis and resulting
impingement.1-6,22 Resulting kinematic changes
from impingement and altered scapular movement
has been linked with a decrease in serratus
anterior muscle activity, an increase in upper
trapezius muscle activity, or an imbalance
between the upper and lower parts of the
trapezius muscle.22 This decrease in activity
may result in a relationship between scapular
stabilizing muscle activity and types of
scapular dyskinesis. There has not yet to be
research done looking at the scapular
stabilizer activity and if an imbalance will
lead to scapular dyskinesis occurring.

Method:

This study was an observational descriptive
study design investigating physically active,
injury-free individuals. Testing took one day
with an observation of scapular dyskinesis
occurring first,then the electromyography data
was collected. For the dyskinesis observation
subjects were asked to hold either 3 lb. or 5
lb. dumbbells while performing four arm
movement; sagittal plane, frontal plane, and
45° with thumbs up and 45° with thumbs down.
While performing the arm movements the subjects

99
were instructed to move at a three beat up and
three beat down rhythm, provided by the
metronome. After the observation electrodes
were placed on the upper trapezius, lower
trapezius, and serratus anterior. These
electrodes were connected to the Biopac MP150
electromyography machine the data was managed
using AcqKnowledge Software. Before performing
the exercises of low- row and push-up-plus the
subjects were instructed to warm up on a green
resistance Theraband® doing low-row, frontal
plane, sagittal plane, humeral abduction, and
humeral extension each performed fifteen times.
After warm-up the subjects were verbally
instructed on how to perform each exercise for
five repetitions and to be done on the same
three beat up and three beat down rhythm with
the metronome as before. The subjects were
allowed to practice this until they were
comfortable with the exercise. A peak
activation measurement was taken for each
muscle during the five repetitions. For each
muscle the data‟s absolute value was taken and
smoothed.
Findings:

The data was analyzed by using a factorial 4x2
MANOVA. There were no significant differences
found with the peak muscle activity with the
two exercises (α=0.246). There was no
significance found between peak muscle activity
and types of scapular dyskinesis observed
(α=0.181). There were trends found however
between types of scapular dyskinesis and
activity of the three scapular stabilizers.

Conclusion:

From this study a trend was found between the
relationship of identifying scapular dyskinesis
and muscle activity. Future testing should
investigate the effects of this relationship.

100
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