Effects of Different Arm Slots on Shoulder Kinematics And

EFFECTS OF DIFFERENT ARM SLOTS ON SHOULDER KINEMATICS AND

KINETICS DURING BASEBALL PITCHING

A Thesis

Presented to the faculty of the Department of Kinesiology

California State University, Sacramento

Submitted in partial satisfaction of the requirements for the degree of

MASTER OF SCIENCE

Kinesiology

(Exercise Science)

Michael Sousa-Johnson, ATC

SPRING 2017

Michael Sousa-Johnson

EFFECTS OF DIFFERENT ARM SLOTS ON SHOULDER KINEMATICS AND

KINETICS DURING BASEBALL PITCHING

A Thesis

Michael Sousa-Johnson

Approved by:

______, Committee Chair

Dr. Rodney Imamura

______, Second Reader

Dr. Rafael Escamilla

______

Date

iii

Student: Michael Sousa-Johnson

I certify that this student has met the requirements for format contained in the University format manual, and that this thesis is suitable for shelving in the Library and credit is to be awarded for the thesis.

______, Graduate Coordinator ______

Dr. Daryl Parker Date

Department of Kinesiology

Abstract

EFFECTS OF DIFFERENT ARM SLOTS ON SHOULDER KINEMATICS AND

KINETICS DURING BASEBALL PITCHING

Michael Sousa-Johnson

INTRODUCTION: Baseball pitchers have the highest volume of throws of all baseball players. These large volumes of throwing may lead to injury of the throwing shoulder.

Each pitcher has their particular throwing style and arm position they prefer, called arm slot. PUROSE: Primary aim was to compare the differences in shoulder abduction angle, lateral trunk lean, and shoulder proximal force, in each arm slot. Secondary aim was to provide evidence for defining ranges for each arm slot and bring about information of a new variable, arm slot angle. METHODS: Motion capture (240 Hz) of fourteen (14) pitchers throwing off an artificial dirt mound in a lab. Data analyzed were shoulder abduction angle, lateral trunk lean, and shoulder proximal force. RESULTS: No statistical significance found comparing shoulder abduction angle or shoulder proximal force (P > 0.05) between arm slot groups. Lateral trunk lean however was significantly different (P < 0.05) between arm slot groups. DISCUSSION: Present study was one of the first to look at differences in shoulder proximal forces between different arm slots.

Limited data to shoulder kinematics and kinetics in literature; however, data has been shown that at ball release there are high amounts of force and torque occurring at the

elbow. Further research needed to look closer into the shoulder forces and torques in each arm slot, and to define ranges for each arm slot as far as arm slot angle.

______, Committee Chair

Dr. Rodney Imamura

______, Date

ACKNOWLEDGEMENTS

To my family whom I love very much and have always been there for me when I needed them the most. To my fiancé, thank you for loving me through all the stress of graduate school and thesis process. To my colleagues and classmates who spent many hours with me in class, in labs, studying until the early hours of the morning, thank you for helping me when I most needed it. To my professors who pushed me further than I could have ever imagined myself, thank you for helping me see my potential. To my undergraduate students who helped me with data collection for this thesis, thank you very much, without you those few days would have been chaotic. To Dr. Alan Hirahara, thank you for pushing me to go above and beyond, to apply for graduate school, and getting interested in the shoulder. To Dr. Daryl Parker, thank you for being a mentor to me academically, professionally and personally. I will always hold you in highest and best regards. To Dr. Rafael Escamilla, thank you for being my toughest critic and showing me there is always more to learn and making be a better scientific writer. To Dr. Rodney

Imamura, thank you for always being in my corner and telling me what I needed to hear.

You have my utmost respect. And finally to my brother, without your unfortunate injury so early in your pitching career I would have never began to ask questions about injury prevention and shoulder injuries.

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TABLE OF CONTENTS

Page

Acknowledgements ...... vii

List of Tables ...... x

List of Figures ...... xi

Chapter

1. INTRODUCTION ...... 1

Background ...... 1

Purpose ...... 4

Hypothesis...... 4

Significance...... 4

Definition of terms ...... 5

Delimitations ...... 6

Limitations ...... 7

2. REVIEW OF LITERATURE ...... 8

Introduction ...... 8

Throwing motion ...... 9

Arm slot ...... 11

Injuries to the throwing shoulder ...... 16

Rotator Cuff ...... 16

Biceps Tendinopathy ...... 16

viii

Labral Tears ...... 17

Posterior Labral Tears ...... 17

SLAP tears ...... 18

Linking biceps and labrum...... 18

EMG studies and biceps...... 20

Conclusion ...... 21

3. METHODS ...... 22

Subject characteristics ...... 22

Study design ...... 23

Equipment ...... 23

Testing Procedures ...... 23

Group Placement ...... 23

Data Collection ...... 24

Data Reduction...... 26

Variables ...... 27

Data analysis ...... 27

4. RESULTS ...... 28

5. DISCUSSION ...... 30

Appendix A. INFORMED CONSENT FORM ...... 34

Appendix B. HEALTH HISTORY FORM ...... 37

References ...... 39

LIST OF TABLES

Tables Page

1. Subject characteristics ...... 22

2. Arm slot group comparison ...... 24

LIST OF FIGURES

Figures Page

1. Definition of “Arm slot angle” ...... 6

2. Phases of throwing ...... 9

3. Overhead arm slot ...... 13

4. Three-quarter arm slot...... 14

5. Sidearm arm slot ...... 15

6. Anatomy of the shoulder girdle ...... 19

7. Reflective markers, front ...... 25

8. Reflective markers, rear ...... 25

9. Shoulder abduction angle ...... 28

10. Shoulder proximal force ...... 29

11. Lateral trunk lean ...... 29

Chapter 1

INTRODUCTION

Background

Shoulder injuries do not present with any particular pattern as to who will sustain an injury and when during their lifetime. As previous research has shown, shoulder injuries affect all stages of life, as well as all populations. From the general population

(Onyekwelu, I., Khatib, O., Zuckerman, J. D., Rokito, A. S., & Kwon, Y. W., 2012), to pediatric athletes (AAOS, 2015, Valovich McLeod, T. C., Decoster, L. C., Loud, K. J.,

Micheli, L. J., Parker, J. T., Sandrey, M. A., & White, C. 2011), and professional athletes

(Smith et al., 2016), anyone can be affected by shoulder injuries. Athletes in particular risk much in regards to their physical health and well-being since their livelihood depends on them participating in their respective sports. If they do not work, they do not get paid. One study of 24 Major League Baseball pitchers tracked their return to play

(RTP) and their return to previous level of pitching (RTPP). The data showed a 62.5%

RTP rate, and among those 86.7% were able to RTPP after shoulder surgery. Though return rate was good, innings pitched (IP) from before surgery (101.8 IP) compared to after surgery (65.53 IP) was significantly reduced (P < 0.004) (Smith et al., 2016). Much research has been done to examine how practitioners can keep athletes healthy and keep them participating in their sports (Fleisig & Andrews, 2012, Oyama 2012, Grantham, W.

J., Byram, I. R., Meadows, M. C., & Ahmad, C. S., 2014), but still more can be done to help the athletes stay healthy during and after their careers.

While any overhead athlete is susceptible to shoulder injuries, baseball pitchers are of particular interest due to their high volume of throwing (Whiteley 2007). Shoulder injuries may not always have a traumatic mechanism, some shoulder injuries may be associated with overuse (Fleisig, G.S., Barrentine, S., Escamilla, R., Andrews J.R., 1996).

One study reported that the biceps brachii muscle can pull the labrum away from the glenoid, especially during the arm cocking and arm deceleration phases of pitching, in a phenomenon further described as the “peel-back mechanism” (Burkhart, 1998). The peel- back mechanism is due to the high amounts of distraction force experienced by pitchers during the arm cocking phase of pitching, with some studies reporting distraction force as high as 1090N (G. S. Fleisig, Andrews, J.R., Dillman, C.J., and & Escamilla, 1995).

Considering that the biceps brachii also assist the rotator cuff muscles in the stabilization of the shoulder, it’s function can be considered an important factor in relation to shoulder injury (Glousman, R., Jobe, F., Tibone, J., Moynes, D., Antonelli, D., & Perry, J. 1988,

Escamilla & Andrews 2009).

It is the goal of competitive baseball pitchers to play their sport as long as they possibly can and have successful career. A shoulder injury is one event that can cut the playing time of an athlete short and since throwing is a major part of pitching, injuries to the throwing arm can have significant consequences to a baseball player’s career.

Whiteley (2007) reported the quantity and distances of throws made by 100 collegiate baseball players over 7 games. The study showed a total of 3328 throws made, a majority

(51%) of which were made by pitchers in the range of 46 to 60 feet (Barrett & Burton,

2002). Over time, these large quantity of throws can lead to a shoulder injury, and further time away from activity (Lesniak et al., 2013).

Matsuo, T., Matsumoto, T., Takada, Y., & Mochizuki, Y. (2000) described the influence of lateral trunk lean on injury-related kinetic parameters by taking pitchers throwing from their unique arm position and simulating a number of different combinations of throwing angles. They found that as contralateral trunk lean increased shoulder shear force decreased. However, the data the authors found were computer simulated and calculated mathematically. Also, the decrease in shear force were not differentiated between pitchers in different arm slot groups. Position of the throwing arm, or arm slot, during baseball pitching is an important aspect to pitching mechanics and has been studied. Likewise, studies that looked into the differences in forces generated by the musculature in the throwing arm during different arm slots have been performed

(Aguinaldo and Chambers 2009, Escamilla and Andrews 2009, Matsuo, T., Matsumoto,

T., Mochizuki, Y., Takada, Y., & Saito, K. 2002, Oyama, S., Yu, B., Blackburn, J. T.,

Padua, D. A., Li, L., & Myers, J. B. 2013). However, none have looked at defining ranges for each arm slot.

Overall, research describing the pitching motion has been well discussed over the years (Fleisig, G. S., Barrentine, S. W., Escamilla, R. F., & Andrews, J. R. 1996; G. S.

Fleisig, 1994; Whiteley, 2007). However, what has not been studied extensively are the differences in angular kinematics and kinetics due to different arm slots. In the present study, “arm slot angle”, as described by the American Sports Medicine Institute (ASMI), is the angle created by two vectors, one vector connecting the throwing shoulder joint

4 center and the throwing hand and a vertical vector from the throwing shoulder (ASMI,

2017). This new variable uses a combination of lateral trunk lean, and shoulder abduction to define a specific angle.

In light of the limited information concerning pitching arm slot and the biomechanics of shoulder injury, further research investigation is necessary. Literature has suggested large shoulder proximal forces, or compressive forces, acting to resist large distraction force as a precursor to shoulder injury. Since arm slot angle is not yet seen in the literature, understanding how different kinematic variables, namely lateral trunk lean and shoulder abduction, affect shoulder kinetics can lead to a better understanding of injury mechanisms and how to prevent these particular mechanisms.

Purpose

The purpose of this study was to compare shoulder proximal force, shoulder abduction, and lateral trunk lean between overhand, three-quarter, and sidearm pitching arm slots.

Hypothesis

The overhead arm slot does increase abduction of the shoulder joint and lateral trunk lean when compared to three-quarter and sidearm arm slots. The overhead arm slot does produce greater proximal force on the shoulder joint when compared to three- quarter and sidearm arm slots.

Significance

Various shoulder injuries caused by repetitive overhead motion commonly lead to shoulder pain and pathology in the overhead athlete (Abrams & Safran, 2010). A better

5 understanding of how these injury mechanisms occur may focus further research of baseball pitching. The differences in shoulder speeds and muscle forces on the joint when comparing the different arm slots to this day is not well understood in the baseball realm and has not been researched (Aguinaldo & Chambers, 2009). Though subtly different, each arm slot is unique in how the pitching arm reacts to activity and how the musculature prevents injuries from occurring (Aguinaldo & Chambers, 2009). There is no current research that compares the shoulder kinematics or kinetics through different arm slots while pitching.

Definition of terms

Kinematics – is the description of linear and angular displacements, velocities and accelerations of joint movements (Winter 2009).

Kinetics – is the general term given to the forces and torques that produce joint movement (Winter 2009).

Arm slot angle – is the angle created by a vertical vector from the throwing shoulder of a pitcher and another vector drawn from the throwing shoulder through the throwing hand of the pitcher. This definition was described by the American Sports Medicine Institute

(ASMI, 2017). Figure 1 below is a visual representation of this angle.

Figure 1. Definition of “arm slot angle” as described by ASMI.

SLAP tear – is a specific type of glenoid labrum tear named by the location of the tear, superior labrum anterior-posterior (Snyder, Karzel, Pizzo, Ferkel, & Friedman, 1990).

Distraction force – is the force experienced when the distal segment attempts to pull away from the joint (Fleisig, G. S., Barrentine, S. W., Escamilla, R. F., & Andrews, J. R.

1996).

Shoulder proximal force – is the force applied onto the glenohumeral joint to counter the distraction force experience during baseball throwing.

Natural arm slot – is the preferred arm slot of the pitcher without mechanical changes imposed by a clinician, coach, or self.

Delimitations

 The time of season this study was performed in is during the off season. This is

considered when the team is not engaging in intercollegiate play; June through

January.

 Age and gender was limited to males minimum of 18 years old.

 Experience required to participate in this study was to have collegiate level

experience, as well as 4 years of pitching instruction. Experience may have been

gathered by participating in any level of college baseball; junior college, Division I,

Division II, Division III, or NAIA.

 Pitchers must have had no history of throwing arm injury in the past 6 months, and no

history of SLAP repair to the throwing shoulder.

 To participate, pitchers must throw from their natural arm slot.

Limitations

 Limitations to this study are that there is no control for right or left handed pitchers,

or whether the pitchers are starters, relievers, or closers.

 In reference to methodology, reflective markers used during this study may fall off

the pitchers while throwing, but will be reapplied immediately.

 The study was also limited by all pitchers pitching in the stretch instead of using a

windup, and all pitchers pitched off an indoor pitching mound in an indoors throwing

facility instead of outdoors in a game environment.

Chapter 2

REVIEW OF LITERATURE

Introduction

When it comes to overhead throwing, pain causes a discontinuation of activity and decline in performance. Most overhead activity in sports have similar mechanics, especially the “overhead sports”. For example, baseball, softball, football, tennis, water polo and swimming, javelin, and volleyball are common and popular “overhead sports” in the United States. Baseball however has been greatly studied and observed to have some of the greatest rotational velocities, forces, and torques of any other overhand sport

(Fleisig et al. 1996, Escamilla and Andrews 2009). Overhead throwing is stressful on the athlete and shoulder joint. A study done by McLeod and Andrews (1986) reviewed patient records over a five year span, and they found that out of 284 cases, 178 (60%) had shoulder injuries related to baseball, and of the 178, 115 (65%) of them were pitchers.

The authors stated that the high percentages of athletes who throw more often, i.e. pitchers, are the athletes who are sustaining these shoulder injuries (McLeod and

Andrews 1986). In another study, 287 elite Major League Baseball pitchers who sustained a shoulder injury and underwent surgery were observed to examine the rate of return to sport. Of these pitchers, only 68% of them returned to sport to pre-injury level in a mean of 12 months, while 22% never returned to play in Major League Baseball (Harris et al., 2013). This review of literature will seek to explain the knowledge of baseball pitching mechanics and injuries that apply to baseball pitchers by describing pitching mechanics, arm slots and prevalent injuries for baseball pitchers.

Throwing motion

The overhead pitching motion is a complex movement to study and understand.

Thus, researchers have broken down the motion into different phases. These phases are wind-up, stride, arm cocking, arm acceleration, arm deceleration and follow-through

(Whiteley 2007). Throughout the phases are defining moments, or events, that are described in biomechanical studies. These include lead foot contact, maximal shoulder external rotation, ball release and maximal shoulder internal rotation (Fleisig et al. 1996).

These phases and events can be seen in Figure 2 below.

Figure 2. Phases of throwing.

Phases and events during the pitching motion are commonly used to examine the forces at the shoulder and the elbow. There is a moderate to strong correlation that has been

10 found in past studies linking some of these events with the greatest amount of force and/or velocities and accelerations during pitching (Aguinaldo and Chambers, 2009;

Fortenbaugh, D., Fleisig, G. S., & Andrews, J. R. 2009). For example, it has been shown that during the late stages of the arm cocking phase high amounts of anterior shoulder force, horizontal adduction torque and internal rotation torque are present (Fortenbaugh et al. 2009).

Different phases cause different forces on the shoulder during overhead throwing activity. With how freely it moves, the shoulder is vulnerable to injury (Li et al. 2010).

During the wind-up phase, there is minimal movement occurring at the shoulder in relation to the kinematics and kinetics. This phase is more of a start to the overall pitching motion, and ends when the pitcher is in a balanced position in preparation for the following phase, which is the stride.

During the stride phase, the shoulder joint begins to move elevating the arm. The shoulder begins to abduct and horizontally abduct in preparation for the arm cocking phase. At this point, lead foot contact occurs and defines the end of the stride phase and the beginning of arm cocking. Studies have used this event as a means to standardize the timing of biomechanical variables; they call lead foot contact 0% of the pitch (Aguinaldo and Chambers 2009, Fortenbaugh et al. 2009).

Following the stride phase is the arm cocking phase. In this phase, the shoulder undergoes high amounts of external rotation and some horizontal adduction to prepare for the arm acceleration phase of pitching. At the end of the arm cocking phase, maximal

external rotation (ERmax) occurs. This event is described as the point at which the maximum range of motion (ROM) occurs for external rotation (Fleisig et al. 1996).

Following the arm cocking phase is arm acceleration phase. In this phase, the shoulder undergoes the greatest rotational change in position when compared to other phases. The shoulder internally rotates at extremely high rates in excess of 6000 degrees per second and even as high as 7550 degrees per second of internal rotation (Fleisig et al.

1996). Also during arm acceleration the shoulder is observed horizontally adducting

(Whiteley 2007). At the end of the arm acceleration phase ball release occurs and similar to lead foot contact, is also used for the timing biomechanical events and normally considered 100% of the throwing motion.

Following the arm acceleration phase is the arm deceleration phase. In this phase the shoulder will undergo large joint moments and proximal forces, also termed compressive forces, at the shoulder to decelerate the arm. During this phase maximal internal rotation (IRmax) occurs and is simply the greatest amount of internal rotation in terms of range of motion.

Following arm deceleration phase is the follow-through phase. This is simply a continuation of the arm deceleration phase. In this phase the shoulder continues to internally rotate and horizontally adduct until the shoulder torques attempt to stop the arm from moving (Fleisig et al. 1996).

Arm slot

All pitching has these six phases and events as previously described. But each pitcher has a style of pitching that is preferred by them, called arm slot. There are four

12 distinct styles of pitching that are known among baseball players, these are overhead, three-quarter, sidearm and submarine; the most well-known being are overhead, and three-quarter arm slots. Each of these styles has their own benefits and drawbacks, and it is up to the individual pitcher to determine the best arm slot that helps them perform the best with the least amount of stress. The arm slot could be likened to a clock, depending on the arm motion looking at the pitcher from home plate. In the methodology for this study, the arm slot angle was measured from the posterior aspect of the pitcher. However, the description and figures that follow will describe the arm slot angle from the anterior aspect of the pitcher.

The “overhead” arm slot can be described as the arm being in the 10:30 to 11:30 position for a right-handed pitcher and 12:30 to 1:30 position for a left-handed pitcher when looking at the pitcher from the anterior aspect. One major factor that causes the arm to be in this position is lateral trunk lean. Contralateral trunk lean away from the throwing arm must be present and as long as the arm is in those higher positions, this could be considered the “overhead” arm slot. The shoulder abduction angle is usually between 90 and 100 degrees (Fleisig et al. 1996). An example of a pitcher who exhibits this arm slot would be Clayton Kershaw as seen in Figure 3 below.

Figure 3. Overhead arm slot.

The “three-quarter” arm slot can be described as the arm being in the 9:30 to

10:30 position for a right-handed pitcher and 1:30 to 2:30 position for a left-handed pitcher when looking at the pitcher from the anterior aspect. The trunk lean to be considered in this arm slot has been observed to be 15-25 degrees of contralateral trunk lean (Fleisig 2010). The shoulder abduction angles is usually found to be between 90 and

100 degrees (Fleisig et al. 1996). An example of a pitcher who exhibits the “three- quarter” arm slot would be Matt Cain as seen in Figure 4 below.

Figure 4. Three-quarter arm slot.

The “sidearm” arm slot can be described as the arm being in the 8:30 to 9:30 position for a right-handed pitcher and 2:30 to 3:30 position for a left-handed pitcher when looking at the pitcher from the anterior aspect. The lateral trunk lean to be considered in this arm slot needs to be close to 0 degrees, or slightly toward the ipsilateral or contralateral side. Shoulder abduction angles will be between 90 and 100 degrees

(Fleisig et al. 1996). The only difference between the “sidearm” and the “submarine” arm slots is that “submarine” pitchers exhibit a greater amount of lateral trunk lean in the ipsilateral direction to the pitching arm. An example of a pitcher who exhibits the

“sidearm” arm slot would be Javier Lopez as seen in Figure 5 below.

Figure 5. Sidearm arm slot.

The shoulder abduction angle between all the arm slots vary little within a range of 10 degrees (Whiteley 2007, Escamilla and Andrews 2009). But forces applied to the shoulder vary among laboratory settings (Whiteley 2007). When kinematic variables change, the forces applied on the joints will change as well. This was seen in studies that varied the subjects’ shoulder abduction angle when throwing (Matsuo et al. 2000, Matsuo et al. 2006, Aguinaldo & Chambers 2009, Fleisig et al. 1996). Though much of the research focuses on the varus torque occurring at the elbow, there is limited information discussing the effect shoulder abduction has on the shoulder tissues. There is a gap in the current research in this regard such that no link has been found for which arm slots have greater incidence rates for particular injuries. The research states there are particular biomechanics that may produce the greatest angular velocities and joint moment at the shoulder, but there is little literature that definitively states which arm slots are at risk for particular injuries at the shoulder joint.

Injuries to the throwing shoulder

Rotator Cuff. There are many different injuries and conditions that will ultimately cause pain and thus a loss of function and performance. One such injury is a rotator cuff tear. The rotator cuff consists of a group of four muscles; supraspinatus

(superior cuff), infraspinatus (posterior cuff), teres minor (posterior cuff) and subscapularis (anterior cuff). Together, their purpose is to stabilize the glenohumeral joint during motion, also known as dynamic stabilizers, and also to assist some movement as accessory muscles to movement. These muscles tear by the same mechanism most other muscle injuries occur, high amounts of tensile forces during eccentric contractions

(McLeod and Andrews 1986). Due to the larger size, subscapularis is not injured quite as often as the other three muscles (McLeod and Andrews 1986). The supraspinatus, infraspinatus and teres minor muscles undergo the most amounts of stress when a pitcher is throwing (Escamilla and Andrews 2009). This is largely due to the compressive, accelerative, and decelerative activity of these muscles during and after the phases of pitching (Escamilla and Andrews 2009, Werner et al. 2001). The theory is that, with the lower mechanical advantage that the supraspinatus and infraspinatus have on controlling the movement of the humerus on the glenoid, fatigue accumulates quicker which causes tearing of the muscles or tendons (McLeod and Andrews 1986).

Biceps tendinopathy. Another injury that is seen among overhead throwing athletes is biceps tendinopathy, and specifically pathologies of the long head of the biceps brachii muscle. Tendinopathy is a catch-all term that describes any pathologies concerning a tendon. Though injuries are not usually seen in younger athletes, the long

17 head of the biceps muscle is an important muscle of the shoulder joint during overhead throwing activity (Escamilla and Andrews 2009). It accelerates shoulder flexion, decelerates shoulder extension and plays an important role in the arm deceleration phase of pitching (Escamilla and Andrews 2009). Typically, this type of injury occurs where the biceps muscle originates. The long head of the biceps brachii muscle originates from the supraglenoid tubercle, which it shares attachment with the superior portion of the glenoid labrum. Whenever the biceps muscle contracts, the tendon applies a tensile force onto the labrum which may lead to tears in the labrum (Andrews, J. R., Carson, W. G., &

Mcleod, W. D. 1985). This force from the long head of biceps brachii muscle, along with the rotator cuff muscles, is what creates the shoulder proximal force discussed in this study.

Labral tears. There are many different implications that can cause injury to the glenoid labrum. There are specific types of labral tears that occur with different mechanisms of injury. The specific types that will be discussed are posterior labral tears, and SLAP tears.

Posterior labral tears. Though the primary mechanism of injury is often a fall on an outstretched arm, this type of labral tear may occur when there is a muscular imbalance in the rotator cuff muscles. If the posterior cuff muscles forcibly contract to prevent anterior translation of the humeral head, and the anterior cuff fails to prevent posterior translation of the humeral head, there will be a large amount of force pulling posteriorly, entrapping the labrum and over time eventually causing a tear. More often seen is a weaker posterior cuff muscle group due to the high frequency of throwing and

18 eccentric contractions to decelerate the throwing motion, but if the subscapular nerve is deactivated due to injury or by another means, this causes the subscapularis to deactivate and thus allow the posterior cuff to overpower it and allow posterior translation of the humeral head.

SLAP tears. The more common type of labral tear among overhead throwing athletes is termed the SLAP tear, or Superior Labrum Anterior-Posterior tear. This type of tear can be broken down further into different types of tears, but for the sake of this report, only Type II tears will be discussed. Type II SLAP tears is described as a detachment of the biceps origin at the supraglenoid tubercle (Snyder et al. 1990). Type II tears can actually be broken down even further into three subcategories, anterior, posterior and combined tears (Morgan et al. 1998). These subcategories simply describe the location of the Type II tear. It has been shown that with the increased number of innings thrown, incidences of injury also increase (Lesniak et al., 2013). But what may cause this labral region to tear could be the tendon that attaches on the superior portion of the labrum, the long head of the biceps brachii muscle.

Linking biceps and labrum

As previously described, the long head of the biceps brachii muscle originates from the superior portion of the glenoid labrum and to the supraglenoid tubercle. This can be seen in Figure 6 below.

Figure 6. Anatomy of the shoulder girdle.

The muscle then inserts on the radial tuberosity of the radius bone. At the elbow, this muscle flexes the elbow and supinates the forearm, but at the shoulder, this muscle is a weak flexor and a weak abductor when in an externally rotated position (Floyd, R. T.

2009). Since the long head of the biceps is an accessory muscle to shoulder flexion, it has a key role in the overhead throwing motion (Escamilla and Andrews 2009). The object of pitching is to accelerate a baseball as much as possible to produce the greatest amount of force onto the ball and thus velocity toward the opposing hitter. Mechanically, the biceps has a number of roles during the overhead motion. It is used in the cocking phase of pitching to stabilize the shoulder joint, it is put on a stretch during a short amount of time in the acceleration phase of pitching, as well as during the deceleration of pitching to slow down the high angular velocity of extension at the elbow (Escamilla and Andrews

2009). The gap in the research is that there has been minimal research to compare different arm slots to differing amounts of shoulder proximal force being applied from the biceps. One study suggested that compression forces preventing distraction of the

20 humerus from the glenoid was the most common mechanism to these superior labrum- biceps complex tears (Maffet, M. W., Gartsman, G. M., & Moseley, B., 1995). Snyder et al. 1990 suggested the most common mechanism of injury was a fall on an outstretched arm. But back in 1985, Andrews et al. observed an association between overhead athletic activity and superior labrum tears (Kim, T. K., Queale, W. S., Cosgarea, A. J., &

McFarland, E. G. 2003). Then in 1998, Burkhart and Morgan suggested that the cause, or at least of posterior Type II SLAP tears, is something called “peel-back” mechanism.

They described this mechanism as a torsional peel-back of the posterosuperior labrum

(Burkhart and Morgan 1998). At this point in the research, little has been done to further study the “peel-back” mechanism and whether this mechanism might be more influential in particular arm slots compared to others.

EMG studies and biceps

Escamilla and Andrews (2009) reviewed previous research that observed muscle activity and recruitment of the shoulder. They observed that athletes with a history of chronic anterior instability use the supraspinatus, infraspinatus and biceps brachii to a greater extent when compared to non-symptomatic throwers during the arm acceleration phase. They also showed that, during the deceleration phase of the pitching motion, the biceps brachii produced the greatest amount of activity. They suggested that during this phase, the biceps brachii works with the other elbow flexors to decelerate elbow extension, which was reported to be approximately 2,300 degrees per second during later parts of arm acceleration. Also, as a secondary function, the biceps brachii works with the rotator cuff to resist distraction and anterior subluxation of the glenohumeral joint. They

21 explained that this muscle activity was observed to occur more in amateur pitchers than in professional pitchers suggesting that amateur pitchers have a less efficient throwing pattern than professional pitchers. Though this review discussed the muscle activity during pitching, there was no differentiation between the muscle activity in different arm slots because it was not examined, which was a limitation for this particular study.

Conclusion

Data and information brought about by this study would be beneficial to the scientific, medical and coaching communities because it would provide new information on distraction forces generated in different arm slots. This may lead to further research suggesting which muscle groups should be focused on when a pitcher is attempting a nonsurgical treatment plan for shoulder injuries. There is need for this information because younger athletes are suffering from injuries that are limiting their playing career.

If shoulder forces and torques are greater in particular arm slots, this may lead to the increase risk of shoulder injuries. Medical professionals need to be able to understand that each arm slot differs in how the shoulder joint musculature and inert tissues react during pitching. Researchers could possibly find a link to other overhead activities and thus further studies to suggest ways to prevent injury across the board.

Chapter 3

METHODS

Subject characteristics

Sixteen (16) subjects participated in the study and subject’s age, height, weight, years of pitching experience, preferred arm slot, and max pitch speed during data collection are shown in Table 1.

Table 1. Subject characteristics.

Age (yrs) Height Weight Years Arm Slot Max Pitch (in) (lbs) Pitching Speed Experience (mph) Subject 1 19 72 170 7 TQ 76.8 Subject 2 20 70 185 10 S 74.2 Subject 3 19 73 182 8 O 80.2 Subject 4 20 77 210 11 TQ 80.9 Subject 5 19 73 210 10 TQ 79.6 Subject 6 19 73 195 8 O 76.8 Subject 7 19 70 178 8 O 76.4 Subject 8 20 73 150 12 TQ 78.9 Subject 9 20 74 150 10 O 80.7 Subject 10 19 74 190 9 O 81.1 Subject 11 20 70 170 9 TQ 77.8 Subject 12 19 76 195 7 TQ 83.3 Subject 13 20 76 170 8 TQ 79.4 Subject 14 19 76 220 7 O 79.6 Subject 15 20 75 220 9 O 82.1 Subject 16 19 77 205 6 TQ 77 Means + 19.4 + 73.7 + 2.3 189.1 + 8.7 + 1.6 79.1 + 2.4 SD 0.5 20.2 *O, overhand; TQ, three-quarter; S, sidearm. Arm slot classification procedure listed in section 2.

All subjects were given an informed consent form approved by the California

State University, Sacramento Institutional Review Board prior to enrollment in the study.

All subjects filled out a health history form and deemed healthy for participation in this study.

Study Design

Equipment

Equipment used for this study was the Qualisys motion capturing system (Oqus

3+, Göteburg, Sweeden). The Qualisys motion capturing system in the lab used 10 cameras that emit infrared light signals that capture the movement of reflective markers at a rate of 240 Hz. Calibrations were executed twice per day, once in the morning and once in the afternoon, for enhanced accuracy of the data collected. Cameras were attached to scaffolding in the laboratory and aimed in the direction of the pitching mound. Subjects threw from an artificial mound with dirt inserts (RFP Practice Mound,

10” Pro Model, Athalonz, Mesa, AZ). Mound can be seen in Figures 7 and 8 below. The volume of space the subject is able to be recorded was approximately 6 feet wide by 10 feet long by 8 feet high. Pitch speed was recorded by a radar gun (Stalker Sport 2,

Applied Concepts, Inc./Stalker Radar, Plano, TX) and measured in miles per hour.

Testing Procedures

Group Placement. First, subjects were categorized into specific groups by their natural arm slot. Each subject was video recorded with the Apple iPhone 5S (Apple Inc.,

Cupertino, CA) while throwing during a normal practice to place the subjects in their respective arm slot group. Camera was directly behind the catcher viewing the subject straight on. Once the video data were collected per subject, each pitcher was placed in an arm slot group. Arm slot angle data provided by the American Sports Medicine Institute

(ASMI) fine-tuned the subject placement. The 7 lowest arm slot angles were placed in the overhand group, and the 7 highest arm slot angles were placed in the three-quarter group.

This “arm slot angle” describes the angle at which a vector drawn from the throwing shoulder to the hand of the pitcher and a vertical vector perpendicular to the ground at the level of the throwing shoulder. Table 2 below shows the difference between groups.

Table 2. Arm slot group comparison.

Age (yrs) Height (in) Weight (lbs) Years Max Pitch Pitching Speed Experience (mph) Overhand 19.4 74.9 187.1 8.7 79.4 Three- 19.3 73.6 194.3 8.4 79.6 quarter P-value 0.6 0.3 0.5 0.8 0.9

Data Collection. Once all subjects were placed in their respective groups, the subjects were scheduled for a testing session. Subjects threw from an artificial mound at the full pitching distance of 60 feet and 6 inches. Subject performed self-selected, non- baseball warm-up exercises followed by self-selected baseball/throwing related warm-up exercise routines. Once the subject felt adequately “warm” and ready to throw, markers were placed on the subject. Reflective markers were attached to the subjects, a total of 38 that measured 0.6 inches in diameter. Figure 7 and 8 below shows the markers attached to the subject from the front and back, respectively.

Figure 7. Reflective markers, front. Figure 8. Reflective markers, rear.

In addition to the markers, each subject also wore their baseball caps, pitching glove, spandex shorts and spikes. The reflective markers were attached to the subject by way of

Velcro and white athletic tape or Leukotape to secure the markers to the body. The markers were placed on the subject’s body and was based on whether the subject threw right- or left-handed. The similar marker placements between right- and left-handed pitchers were: top head, front head, right/left head, right/left clavicle, right/left shoulder,

C7, right/left medial/lateral epicondyle of the humerus, right/left medial/lateral styloid process of the wrist, right/left anterior superior iliac spine (ASIS), right/left posterior superior iliac spine (PSIS), right/left trochanter, right/left medial/lateral epicondyle of the femur, right/left medial/lateral malleolus, and right/left toe. The markers specific to right-

26 handed pitchers were: right scapula on inferior angle, right proximal ulna, left distal ulna, right hand, and left heel. The markers specific to left-handed pitchers were: left scapula on inferior angle, left proximal ulna, right distal ulna, left hand, and right heel. The subjects threw at a target (strike zone) located 60.5 feet from the pitching mound rubber with target dimensions of 30 inches tall by 18 inches wide raised approximately 20 inches above the ground. Pitchers were instructed that each throw for data collection needed to be at maximum effort. Pitchers threw a total of 10 pitches from the dirt mound in the stretch and instructed to throw a “fastball”, either 2 seam fastball or 4 seam fastball, which ever elicited the greatest velocity for them.

Data Reduction. Pitch selection for data analysis followed the order of: 1) strike,

2) greatest velocity. Three pitches with the greatest velocities of the strikes thrown were accepted for data analysis. If there were less than three strikes thrown, the pitches closest to the strike zone were selected for analysis, followed by greatest velocity. After data were collected and pitch trials selected, processing procedures were performed.

Procedures included cropping the file length to capture pitching motion just before maximum knee height and just after follow-through, markers that had gaps throughout the motion capture were filled, position data was exported and put into format prescribed by the American Sports Medicine Institute (ASMI). Data was then sent to ASMI for analysis.

Of the sixteen (16) subjects tested, only data from fourteen (14) of the subjects were processed and calculated by ASMI BioPitch© 12.0 program. The two subjects were removed from this study because one subject due to n = 1 (sidearm group), and the other

27 subject had a marker forgotten to be attached during data collection (three-quarter group).

Therefore, each of the two groups (overhand group and three-quarter group) each had seven subjects (n = 7).

Variables. The independent variable was the arm slot the pitchers prefer, either overhead or three-quarter. The main dependent variable that was measured was the shoulder proximal force, defined as the force required to maintain the humeral head in the glenoid fossa, at the throwing shoulder near ball release. Additional kinematic variables were also collected to define the different arm slots. The kinematic dependent variables that were measured were shoulder abduction, and lateral trunk lean, described as the angle of the trunk in relation to the vertical Z-axis in the YZ plane, using a proprietary program created and ran by ASMI called BioPitch© 12.0. The shoulder proximal force at the shoulder was also calculated using the same BioPitch© 12.0 program.

Data Analysis

Data was recorded in means + standard deviation. Data was then analyzed using

Microsoft Excel for statistical analysis. A one-tailed, unpaired with equal variance independent student T-Test was ran for statistical analysis and level of significance will be set at P < 0.05 between the two arm slot groups for shoulder proximal force, shoulder abduction, and lateral trunk lean.

Chapter 4

RESULTS

Of our two hypotheses, both were not supported by the results. The overhand arm slot did not show greater shoulder abduction angles, overhand group showed a mean of

90˚ + 7 ˚, while the three-quarter group showed 86˚ + 10˚, nor did it show greater shoulder proximal force, overhand group showed a mean of 940N + 92N, while the three- quarter group showed 928N + 121N. Figures 9 and 10 show the findings of shoulder abduction angle and shoulder proximal force between the two groups, respectively. A secondary aim of this study was to provide more information about how to define arm slot incorporating trunk measurement. There was a significant difference (P < 0.05) in the amount of lateral trunk lean between the groups, overhand group showed a mean of 28˚ +

9˚, while the three-quarter group showed 19˚ + 8˚. This is shown below in Figure 11.

Shoulder Abduction 120

100

60 Overhand Three-Quarter 40

Angle Degrees) Angle (˚, 20

0 Arm Slot

Figure 9. Shoulder abduction angle.

Shoulder Proximal Force 1200

1000

800

600 Overhand Three-Quarter 400

Force (N,Newtons) Force 200

0 Arm Slot

Figure 10. Shoulder proximal force.

Lateral Trunk Lean 40 35 30 25 20 Overhand 15 Three-Quarter

10 Angle Degrees) Angle (˚, 5 0 Arm Slot

Figure 11. Lateral trunk lean.

Chapter 5

DISCUSSION

Of the three dependent variables examined in this present study, there was only statistical significance found in lateral trunk lean. Each of the variables, lateral trunk lean, shoulder abduction, and shoulder proximal force, all play a critical role in baseball pitching (Fleisig et al 1995). Feltner and Dapena in 1986 showed that shoulder proximal force, defined as the force required to maintain the humeral head in the glenoid fossa, was 860N + 120N. Later in 1995, Fleisig et al then showed the same force to be in upwards of 1090N + 110N. The findings of the present study (934N + 103N for all the subjects combined) are in agreement with previous studies.

The present study was the first to specifically examine shoulder proximal forces between different arm slot groups. The overhand group in this study showed to have a mean of 940N + 92N, while the three-quarter group had a mean of 928N + 121N.

Possibly due to low number of subjects, no statistical significance was found.

Other studies have found significant differences in kinetic variable when comparing different arm slots, however they were not the same variables as discussed in the present study. Aguinaldo and Chambers (2009) measured the effect of sequential body motion on elbow valgus torque during baseball pitching. This study took pitchers who threw from the overhand (55) and sidearm (14) arm slot positions. The authors found that elbow valgus torques were greater in the sidearm arm slot position (66 + 24

N∙m) than in the overhand arm slot position (46 + 29 N∙m). A second group that showed greater elbow valgus torque were pitchers who initiated trunk rotation before foot contact

31 compared to after foot contact (P = 0.02). However the authors grouped pitchers who threw in the overhand and three-quarter arm slots together, which they called “overhand”, which differs from the present study.

In another study, Matsuo and colleagues (2006) examined the effects of shoulder abduction and lateral trunk lean angles on elbow varus torque. They simulated 42 motions for each pitcher, and calculated the peak elbow varus torque for each simulated motion. The simulations showed that both shoulder abduction and lateral trunk lean affected the peak elbow varus torque and the interaction between shoulder abduction and lateral trunk lean was also significant (P < 0.0001). As trunk lean to the contralateral side increased, the shoulder abduction angle producing the minimum peak elbow varus torque decreased. If lateral trunk lean and shoulder abduction angles affected elbow varus torque, why can they not also affect shoulder proximal force?

Solomito and colleagues sought to determine if there was associations between contralateral trunk lean, ball velocity, and moments at the shoulder and elbow joints

(Solomito, Garibay, Woods, Ounpuu, & Nissen, 2015). They found that for every 10˚ increase in contralateral trunk lean there was an increase in ball speed of 0.5 meter per second (P = 0.003), as well as an increase in elbow varus torque of 3.5 N∙m (P < 0.001) and an increase in shoulder internal rotation torque of 2.7 N∙m (P < 0.001). With an increasing torque, there should also be an increase in force. This increase in force should be further studied.

This study brought light to a new variable described by ASMI as “arm slot angle”.

This angle describes the angle at which a vector drawn from the throwing shoulder to the

32 hand of the pitcher and a vertical vector perpendicular to the ground at the level of the throwing shoulder (ASMI, 2017). This new variable provides an easy visual representation of different arm slots and ranges can be set to describe which arm slot a pitcher may be in for coaches, clinicians, physicians, athletes and others alike. Though these ranges have not been discussed yet, future studies between biomechanists, baseball coaches and pitchers could bring about textbook-like definitions to the scientific community to further arm slot studies that examining different biomechanical variables with different arm slots.

One limitation to the current study was that there was a relatively small sample size for each of the groups. With an n = 7 for both groups, it can be difficult to find any statistical significance. To counteract this limitation, increasing the sample size could prove to benefit the researchers. A second limitation was that our subjects were placed in groups by means of a video captured by the researchers. After this, the author used the arm slot angle provided by ASMI to augment the subject classification and further affirm subjects into their correct groups. The 7 lowest angles were put into the overhand group and the highest seven were put into the three-quarter group. “Arm slot angle” could provide an easier method to classify subjects per arm slot. In the present study, there was no range of what classifies overhand or three-quarter arm slot, so there is a possibility that some subjects were not in the correct group. Future studies should be conducted to provide ranges of “arm slot angles” that describe all of the arm slots; overhand, three- quarter, sidearm and even submarine. Another limitation was that data was collected before the season began. The subjects had had a full Fall season worth of workouts and

33 practice, but they had also just come off a month long break from baseball activity, hence the relatively low max pitch velocities. Also, the testing was performed at the beginning of January of 2017 during a cold front with rainy and windy conditions. The ambient temperature in the lab was on average 50˚F, this is very cold for baseball pitching considering it is a Spring sport.

In conclusion, there was no difference in shoulder abduction angle or shoulder proximal force between overhand and three-quarter arm slot pitchers, but there was a significant difference in the amount of lateral trunk lean between overhand and three- quarter arm slot pitchers. Arm slot angle is a new concept and variable provided by

ASMI and should be used in future studies as a means of categorizing groups to separate subjects by their arm slots, namely overhand, three-quarter and sidearm. Defining ranges of each of the arm slots should also be described. Future studies should examine how all of the aforementioned topics interact. Repeating these studies to look into how shoulder proximal force reacts to the different arm slots could provide a better understanding of the injury mechanics that occur during baseball pitching.

Appendix A: INFORMED CONSENT FORM

Effects of Different Arm Slots on Shoulder Angular Kinematics and Kinetics During

Baseball Pitching

You are invited to participate in a research study which will involve pitching from an artifitial mound with turf and dirt in the Department of Physical Therapy

Biomechanics Laboratory at Sacramento State and motion analysis of your pitching mechanics and forces acting on the shoulder. My name is Michael Sousa-Johnson, and I am a Masters student and the primary investigator in this study at California State

University, Sacramento, and Department of Kinesiology. You were selected as a possible participant in this study because you are a collegiate baseball pitcher and stated on your health history form you have no history of throwing arm injury in the last 6 months or history of shoulder surgery in your career.

Your participation in this project is voluntary, and will only last one day or possibly two days if the data collected from you is unanalyzable. Even after you sign the informed consent document, you may decide to leave the study at any time without penalty or risk.

The purpose of this research is to investigate the forces and speeds the shoulder joint undergoes during baseball pitching with respect to individual arm slot. If you decide to participate, after signing the consent form, you will be asked to throw 10 to 30 pitches from an artificial mound with turf and dirt in a lab with infrared cameras capturing your

35 motion with reflective markers attached to your bare skin with double-sided tape and/or white athletic tape for motion analysis. You will also be wearing a force/pressure sensor in your shoe during data collection. Your participation in this study will only require one to two days for a debriefing and data collection. Each session will last up to two hours for data collection.

There are possible risks of loss of confidentialtiy and physical injury. If you begin to experience pain during the study, you will be asked to stop and contact your personal health physician. Any information that is obtained in connection with this study and that can be identified with you will remain confidential and will be disclosed only with your permission. Measures to insure your confidentiality are all data, signed papers, motion capture, iPhone video, injury information, etc. will be kept in an encypted computer, in a locked office, in a locked lab. Video from the iPhone used for categorization of arm slot will be transferred to an encrypted computer and immediately erased from the iPhone. No one but me will have access to personal information. The data obtained will be maintained in a safe, locked location and will be destroyed after a period of three years after the study is completed.

There are some benefits to this research, particularly that you will get to experience motion capturing in the scientific realm. Your data will help build the body of knowledge in science to better understand the mechanics of baseball throwing.

If you have any questions about the research at any time, please contact me at

(209) 535-5176 or Rodney Imamura, Ph.D. at [email protected]. If you have any questions about your rights as a participant in a research project please contact the Office

36 of Research Affairs, California State University, Sacramento, (916) 278-5674, or email [email protected]. In the event of a research-related injury, please contact your regular medical provider and bill through your normal insurance carrier, and then advise us.

Your signature below indicates that you have read and understand the information provided above, that you willingly agree to participate, that you may withdraw your consent at any time and discontinue participation at any time without penalty or loss of benefits to which you are otherwise entitled, and that you are not waiving any legal claims, rights or remedies.

Signature Date

______

Appendix B: HEALTH HISTORY FORM

Health History Form Age: ______Year in School: ______Years Experience (Pitching): ______Throwing arm: ______Height: ______Weight: ______History of injury in the last 6 months: Yes / No If yes, state the injury, when the injury was sustained, and when you were cleared from the injury: ______History of surgery: Yes / No If yes, state the surgery, when the surgery was performed, and when you were cleared from the surgery: ______

I certify that to the best of my knowledge all of the above statements are true and no information was withheld.

Signature: ______Date: ______

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