Lower Trapezius Muscle Contribution to Shoulder Impingement and Scapular Dyskinesis

LOWER TRAPEZIUS MUSCLE CONTRIBUTION TO SHOULDER IMPINGEMENT AND

SCAPULAR DYSKINESIS

Chapter 1: introduction

The complex human anatomy and biomechanics of the shoulder absorbs a large amount

of stress while performing activities like throwing a baseball, swimming, overhead material

handling, and other repetitive overhead activities. The term “shoulder impingement”, first

described by Neer (Neer, 1972), clarified the etiology, pathology, and treatment of a common

shoulder disorder. Initially, patients who were diagnosed with shoulder impingement were

treated with subacromial decompression, but Tibone (Tibone, et al., 1985) demonstrated that

overhead athletes had a success rate of only 43% and only 22% of throwing athletes were able to

return to sport. Therefore, surgeons sought alternative causes of the overhead throwers pain.

Jobe (Jobe, Kvitne, & Giangarra, 1989) then introduced the concept of instability, which would

result in secondary impingement, and hypothesized that overhead throwing athletes develop

shoulder instability and this instability in turn led to secondary subacromial impingement. Jobe

(Jobe, 1996) also later described the phenomenon of “internal impingement” between the

articular side of the posterior rotator cuff and the posterior glenoid labrum while the shoulder is

in abduction and external rotation.

From the above stated information, it is obvious that shoulder impingement is a common

condition affecting overhead athletes and this condition is further complicated due to the

throwing motion being a high velocity, repetitive, and skilled movement (Wilk, et al., 2009;

Conte, Requa, & Garrick, 2001). During the throwing motion, an extreme amount of force is

placed on the shoulder including an angular velocity of nearly 7250˚/s and distractive or

translatory forces less than or equal to a person’s body weight (Wilk, et al., 2009). For this

reason, the glenohumeral joint is the most commonly injured joint in professional baseball

pitchers (Wilk, et al., 2009) and other overhead athletes (Sorensen & Jorgensen, 2000).

Consequently, an overhead athlete’s shoulder complex must maintain a high level of muscular

strength, adequate joint mobility, and enough joint stability to prevent shoulder impingement or

other shoulder pathologies (Wilk, et al., 2009; Sorensen & Jorgensen, 2000; Heyworth &

Williams, 2009; Forthomme, Crielaard, & Croisier, 2008).

Once pathology is present typical manifestations include a decrease in throwing

performance, strength deficits, decreased range of motion, joint laxity, and/or pain (Wilk, et al.,

2009; Forthomme, Crielaard, & Croisier, 2008). It is important for a clinician to understand the

causes of abnormal shoulder dynamics in overhead athletes with impingement in order to

implement the most effective and appropriate treatment plan and maintain wellness after

pathology. Much of the research in shoulder impingement is focused on the kinematics of the

shoulder and scapula, muscle activity during these movements, static posture, and evidence

based exercise prescription to correct deficits. Despite the research findings, there is uncertainty

as to the link between kinematics and the mechanism of for SIS in overhead athletes. The

purpose of this paper is to review the literature on the pathomechanics, EMG activity, and

clinical considerations in overhead athletes with impingement.

1.1 SIGNIFICANCE OF DISSERTATION

The goal of this project is to investigate the electromyographic (EMG) activity of the

lower trapezius during commonly used therapeutic exercises for individuals with shoulder

impingement and to determine the effect the lower trapezius has on scapular dyskinesis. Each

therapeutic exercise has a specific EMG profile and knowing this profile is beneficial to help a

rehabilitation professional determine which exercise dosage and movement pattern to select

muscle rehabilitation. In addition, the data from study one of this dissertation was used to pick

the specific exercise which exhibited the highest potential to activate and fatigue the lower

trapezius. From fatiguing the lower trapezius, we are able to determine the effect fatigue plays in

inducing scapula dyskinesis and increasing the injury risk of that individual. This is important in

preventing devastating shoulder injuries as well as overall shoulder health and wellness and these

studies may shed some light on the mechanism responsible for shoulder impingement and injury.

CHAPTER 2: LITERATURE REVIEW

This review will begin by discussing the history, incidence, and epidemiology of

shoulder impingement in Section 1.0, which will also discuss the relevant anatomy and

pathophysiology of the normal and pathologic shoulder. The next section, 2.0, will cover the

specific and general limitations of EMG analysis. The following section, 3.0, will discuss

shoulder and scapular movements, muscle activation, and muscle timing in the healthy and

impinged shoulder. Finally, section 4.0 will discuss the clinical implications and the effects of

rehabilitation on the overhead athlete with shoulder impingement.

2.1 HISTORY, INCIDENCE, AND EPIDEMIOLOGY OF SHOULDER IMPINGEMENT

Shoulder impingement accounts for 44%-65% of all cases of shoulder pain (Neer, 1972; Van

der Windt, Koes, de Jong, & Bouter, 1995) and is commonly seen in overhead athletes due to the

biomechanics and repetitive nature of overhead motions in sports. Commonly, the most affected

types of sports activities include throwing athletes, racket sports, gymnastics, swimming, and

volleyball (Kirchhoff & Imhoff, 2010).

Subacromial impingement syndrome (SIS), a diagnosis commonly seen in overhead athletes

presenting to rehabilitation, is characterized by shoulder pain that is exacerbated with arm

elevation or overhead activities. Typically the rotator cuff, the long head of the biceps tendon,

and/or the subacromial bursa are being “impinged” under the acromion in the subacromial space

causing pain and dysfunction (Ludewig & Cook, 2000; Lukaseiwicz, McClure, Michener, Pratt,

& Sennett, 1999; Michener, Walsworth, & Burnet, 2004; Nyberg, Jonsson, & Sundelin, 2010).

Factors proposed to contribute to SIS can be classified as either intrinsic or extrinsic and then

further classified, based on the cause of the problem, into primary, secondary, or posterior

impingement (Nyberg, Jonsson, & Sundelin, 2010).

2.1.1 Relevant anatomy and pathophysiology of shoulder complex

When discussing the relevant anatomy in shoulder impingement, it is important to have an

understanding of the glenohumeral and scapula-thoracic musculature, subacromial space (SAS),

and soft tissue which can become “impinged” in the shoulder. The primary muscles of the

shoulder complex include the rotator cuff (RTC) (supraspinatus, infraspinatus, teres minor, and

subscapularus), scapular stabilizers (rhomboid major and minor, upper trapezius, lower trapezius,

middle trapezius, serratus anterior), deltoid, and accessory muscles (latisimmus dorsi, biceps

brachii, coracobrachialis, pectoralis major, pectoralis minor). The shoulder also contains

numerous bursae, one of which is clinically significant in overhead athletes with impingement

called the subacromial bursae. The subacromial bursa is located between the deltoid muscle and

the glenohumeral joint capsule and extends between the acromion and supraspinatus muscle.

Often, with repetitive overhead activity, the subacromial bursae may become inflamed causing a

reduction in the subacromial space (Wilk, Reinold, & Andrews, 2009). The supraspinatus

tendon lies underneath the subacromial bursae and inserts on the superior facet of the greater

tubercle of the humerus and is the most susceptible to impingement of the RTC muscles. The

infraspinatus tendon inserts posterior-inferior to the supraspinatus tendon on the greater tubercle

and may become impinged by the anterior acromion during shoulder movement.

The SAS is a 10mm area below the acromial arch in the shoulder (Petersson & Redlund-

Johnell, 1984) and contains numerous soft tissue structures including tendons, ligaments, and

bursae (Figure 1). These structures can become compressed, or “impinged”, in the SAS causing

pain due to excessive humeral head migration, scapular dyskinesis, muscular weakness, and

bony abnormalities. Any subtle deviation (1-2 mm) from a normal decrease in the SAS can

contribute to impingement and pain (Allmann, et al., 1997; Michener, McClure, & Karduna,

2003). Researchers have compared static radiographs of painful and normal shoulders at

numerous positions of glenohumeral range of motion, and the findings include: 1) humeral head

excursion greater than 1.5 mm is associated with shoulder pathology (Poppen & Walker, 1976),

2) patient’s with impingement demonstrated a 1mm superior humeral head migration (Deutsch,

Altchek, Schwartz, Otis, & Warren, 1996), 3) patient’s with RTC tears (with and without pain)

demonstrated superior migration of the humeral head with increasing elevation between 60°-

150° compared to a normal control (Yamaguchi, et al., 2000), and 4) in all studies, it was

demonstrated that a decrease in SAS was associated with pathology and pain.

To maintain the SAS, the scapula upwardly rotates which will elevate the lateral

acromion and prevent impingement, but the SAS will exhibit a 3mm-3.9mm decrease in non-

pathologic subjects at 30-120 degrees of abduction (Ludewig & Cook, 2000; Graichen, et al.,

1999).

Scapular posterior tilting also prevents impingement of the RTC tendons by elevating

the anterior acromion and maintaining the SAS.

Shoulder impingement, believed to contribute to the development of RTC disease

(Ludewig & Braman, 2011; Van der Windt, Koes, de Jong, & Bouter, 1995), is the most

frequently diagnosed shoulder disorder in primary healthcare and despite its reported prevalence,

the diagnostic criteria and etiology of SIS are debatable (Ludewig & Braman, 2011). SIS is an

encroachment of soft tissues in the SAS due to narrowing of this space (Figure 1, B), and after

impingement occurs the shoulder soft tissue can and may progress through the 3 stages of

lesions (typically and overhead athlete progresses through these stages more rapidly)(Wilk,

Reinold, Andrews, 2009). Neer described (Neer, 1983) three stages of lesions (Table 1) and the

higher the stage the harder to respond to conservative care.

Table 1: Neer classifications of lesions in impingement syndrome

Stage Characteristics Typical Age of Patient

Stage I edema and hemorrhage of the bursa and cuff,

reversible with conservative treatment

< 25 y.o.

Stage II irreversible changes, such as fibrosis and

tendinitis of the rotator cuff

25-40 y.o.

Stage III by partial or complete tears of the rotator cuff

and/ or biceps tendon and acromion and/or

AC joint pathology

>40 y.o.

SIS can be separated into two main mechanistic theories and two less classic forms of

impingement. The two main theories include Neer’s (Neer, 1972) impingement theory which

focuses on the extrinsic mechanisms (primary impingement) and the second theory focuses on

intrinsic mechanisms (secondary impingement). The less classic forms of shoulder impingement

include internal impingement and coracoid impingement.

Primary shoulder impingement results from mechanical abrasion and compression of the

RTC tendons, subacromial bursa, or long head of the biceps tendon under the anterior

undersurface of the acromion, coracoacromial ligament, or undersurface of the

acromioclavicular joint during arm elevation (Neer, 1972). This type of impingement is

typically seen in persons older than 40 years old and is typically due to degeneration. Scapular

dyskinesis has been observed in this population and causes superior translation of the humeral

head, further decreasing the SAS (Lukaseiwicz, McClure, Michener, Pratt, & Sennett, 1999;

Ludewig & Cook, 2000; de Witte, et al., 2011).

In some studies, a correlation between acromial shape (Bigliani classification type II or

type III) (Figure 1) (Bigliani, Morrison, & April, 1986) and SIS has been observed and it is

presumed that the hooked acromion is a pre-existing anatomic variation or traction spur caused

by repetitive superior translation of the humerus or by tendinopathy (Nordt, Garretson, &

Plotkin, 1999; Hirano, Ide, & Takagi, 2002; Jacobson, et al., 1995; Morrison, 1987). This

subjective classification has applied to acromia studies using multiple imaging types and has

demonstrated poor to moderate intra-observer reliability and inter-observer repeatability.

Figure 1: Bigliani classification of acromion shapes based on a supraspinatus outlet view on a

radiograph (Bigliani, Morrison, & April, 1986; Wilk, Reinold, & Andrews, 2009).

Other studies conclude that there is no relation between SIS and acromial shape, or

discuss the difficulties of using subacromial shape as an assessment tool (Bright, Torpey, Magid,

Codd, & McFarland, 1997; Burkhead & Burkhart, 1995). Commonly, partial RTC tears are

referred to as a consequence of SIS and it would be expected that these tears would occur on the

bursal side of the RTC if it is “impinged” against a hooked acromion. However, the majority of

partial RTC tears occur either intra-tendinous or on the articular side of the RTC (Wilk, Reinold,

& Andrews, 2009). Despite these discrepancies, the extrinsic mechanism forms the rationale for

the acromioplasty surgical procedure, which is one of the most commonly performed surgical

procedures in the shoulder (de Witte, et al., 2011).

The second theory of shoulder impingement is based on degenerative intrinsic

mechanisms and is known as secondary shoulder impingement. Secondary shoulder

impingement results from intrinsic breakdown of the RTC tendons (most commonly the

supraspinatus watershed zone) as a result of tension overload and ischemia. It is typically seen

in overhead athletes from the age of 15-35 years old and is due to problems with muscular

dynamics and associated shoulder or scapular instability (de Witte, et al., 2011). Typically, this

condition is enhanced by overuse, subacromial inflammation, tension overload on degenerative

RTC tendons, or inadequate RTC function leading to an imbalance in joint stability and

mobility, with consequent altered shoulder kinematics (Yamaguchi, et al., 2000; Mayerhoefer,

Breitenseher, Wurnig, & Roposch, 2009; Uhthoff & Sano, 1997). Instability is generally

classified as traumatic or atraumatic in origin, as well as by the direction (anterior, posterior,

inferior, or multidirectional) and amount (grade I- grade III) of instability (Wilk, Reinold, &

Andrews, 2009). Instability in overhead athletes is typically due to repetitive microtrauma,

which can contribute to secondary shoulder impingement (Ludewig & Reynolds, 2009).

Recently, internal impingement has been identified and thought to be caused by friction

and mechanical abrasion of the undersurface of the supraspinatus and infraspinatus against the

anterior or posterior glenoid rim or glenoid labrum.

This has been seen posteriorly in overhead athletes when the arm is abducted to 90

degrees and externally rotated (Pappas, et al., 2006) and is usually accompanied with complaints

of posterior shoulder pain during this late cocking phase of throwing when the arm is at the end

range of external rotation (Myers, Laudner, Pasquale, Bradley, & Lephart, 2006). Posterior

shoulder tightness (PST) and glenohumeral internal rotation deficit (GIRD) have also been

linked to internal impingement by Burkhart and colleagues (Burkhart, Morgan, & Kibler, 2003).

Correction of the PST through physical therapy has been shown to lead to resolution of the

symptoms of internal impingement (Tyler, Nicholas, Lee, Mullaney, & Mchugh, 2012).

Coracoid impingement is typically associated with anterior shoulder pain at the extreme

ranges of glenohumeral internal rotation (Jobe, Coen, & Screnar, 2000). This type of

impingement is less commonly discussed but consists of the subscapularis tendon being

impinged between the coracoid process and lesser tuberosity of the humerus (Ludewig &

Braman, 2011).

Since the RTC muscles are involved in throwing and overhead activities, partial thickness

tears, full thickness tears, and rotator cuff disease is seen in overhead athletes. When this

becomes a chronic condition, secondary impingement or internal impingement can result in

primary tensile cuff disease (PTCD) or primary compressive cuff disease (PCCD). PTCD,

hypothesized to be a byproduct of internal impingement, occurs during the deceleration phase of

throwing in a stable shoulder and is the result of large repetitive eccentric loads placed on the

RTC as it attempts to decelerate the arm resulting in partial undersurface tears in the

supraspinatus and infraspinatus tendons (Andrews & Angelo, 1988; Wilk, et al., 2009). In

contrast, PCCD occurs on the bursal side of the RTC and results in partial thickness tears of the

RTC. It is hypothesized that processes that cause a decrease in the SIS increase the risk of this

pathology and this is a byproduct of RTC muscular imbalance and weakness especially during

the deceleration phase of throwing (Andrews & Angelo, 1988). During the late cocking and

early acceleration phases of throwing, with the arm at maximal external rotation, the rotator cuff

has the potential to become impinged between the humeral head and the posterior-superior

glenoid, internal or posterior impingement (Wilk, et al., 2009), and may cause articular or

undersurface tearing of the RTC in overhead athletes.

In conclusion, tears of the RTC may be caused by primarily 3 mechanisms in overhead

athletes including internal impingement, primary tensile cuff disease (PTCD), or primary

compressive cuff disease (PCCD) (Wilk, et al., 2009) and the causes of SIS are multifactorial

and variable.

2.2 HISTORY, INCIDENCE, AND EPIDEMIOLOGY OF SCAPULA DYSKINESIS

The scapula and its associated movements are a critical component facilitating normal

functional movements in the shoulder complex, while maintaining stability of the shoulder and

acting as an area of force transfer (Kibler & McMullen, 2003). Assessing scapular movement

and position is an important part of the clinical examination (Wright, et. al., 2012) and identifies

the presence or absence of optimal motion in order to guide specific treatment options (Ludwig

& Reynolds, 2009). The literature lacks the ability to identify if altered scapula positions or

motions are specific to shoulder pathology or if these alterations are a normal variation (Wright,

et al., 2012). Scapula motion abnormalities consist of premature, excessive, or dysrhythmic

motions during active glenohumeral elevation, lowering of the upper extremity or upon bilateral

comparison (Ludwig & Reynolds, 2009; Wright, et al., 2012). Research has demonstrated that

the scapula upwardly rotates (Ludwig & Reynolds, 2009), posteriorly tilts, and externally rotates

to clear the acromion from the humerus in forward elevation. Also, the scapula synchronously

externally rotates while posteriorly tilting to maintain the glenoid as a congruent socket for the

moving arm and maximize concavity compression of ball and socket kinematics. The scapula is

also dynamically stabilized in a position of retraction during arm use to maximize activation and

length tension relationships of all muscles that originate on the scapula (Ludwig & Reynolds,

2009). Finally, the scapula is a link in the kinetic chain of integrated segment motions that starts

from the ground and ends at the hand (Kibler, Ludewig, McClure, Michener, Bak, Sciascia,

2013). Because of the important but minimal bony stabilization of the scapula by the clavicle

through the acromioclavicular joint, dynamic muscle function is the major method by which the

scapula is stabilized and purposefully moved to accomplish its roles. Muscle activation is

coordinated in task specific force couple patterns to allow stabilization of position and control of

dynamic coupled motion. Also, the scapula will assist with acromial elevation to increase

subacromial space for underlying soft tissue clearance (Ludwig & Reynolds, 2009; Wright, et al.,

2012) and, for this reason, changes in scapular position are important.

The clavicle exists to help maintain optimal scapular position during arm motion (Ludwig &

Reynolds, 2009). In this manner, it acts as a strut for the shoulder as it attaches the arm to the

axial skeleton via the acromioclavicular and sternoclavicular joints. Injury to any of the static

restraints can cause the scapula to become unstable, which in turn will negatively affect arm

function (Kibler & Sciascia, 2010).

Previous research has found that changes to scapular positioning or motion were evident in

68% to 100% of patients with shoulder impairments (Warner, Micheli, Arslanian, Kennedy, &

Kennedy, 1992) resulting in compensatory motions at distal segments. The motions begin

causing a diminished dynamic control of humeral-head deceleration and lead to shoulder

pathologies (Voight, Hardin, Blackburn, Tippett, & Canner, 1996; Wilk, Meister, & Andrews,

2002; McQuade, Dawson, & Smidt, 1998; Kibler & McMullen, 2003; Warner, Micheli,

Arslanian, Kennedy, & Kennedy, 1992; Nadler, 2004; Hutchinson & Ireland, 2003). For this

reason, the effects of scapular fatigue warrants further research.

Scapular upward rotation provides a stable base during overhead activities and previous

research has examined the effect of fatigue on scapula movements and shoulder function

(Suzuki, Swanik, Bliven, Kelly, & Swanik, 2006; Birkelo, Padua, Guskiewicz, & Karas, 2003;

Su, Johnson, Gravely, & Karduna, 2004; Tsai, McClure, & Karduna, 2003; McQuade, Dawson,

& Smidt, 1998; Joshi, Thigpen, Bunn, Karas, & Padua, 2011; Tyler, Cuoco, Schachter, Thomas,

& McHugh, 2009; Noguchi, Chopp, Borgs, & Dickerson, 2013; Chopp, Fischer, & Dickerson,

2011; Madsen, Bak, Jensen, & Welter, 2011). Prior studies found no change in scapula upward

rotation due to fatigue in healthy individuals (Suzuki, Swanik, Bliven, Kelly, & Swanik, 2006)

and healthy overhead athletes (Birkelo, Padua, Guskiewicz, & Karas, 2003; Su, Johnson,

Gravely, & Karduna, 2004). However, the results of these studies should be interpreted with

caution and may not be applied to functional movements since one study (Suzuki, Swanik,

Bliven, Kelly, & Swanik, 2006) performed seated overhead throwing before and after fatigue

with healthy college age men. Since the kinematics and dynamics of overhead throwing cannot

be seen in sitting, the author’s results can’t draw a comparison to overhead athletes or the

pathological populations since the participants were healthy. Also, since the scapula is thought

to be involved in the kinetic chain of overhead motion (Kibler, Ludewig, McClure, Michener,

Bak, & Sciascia, 2013), sitting would limit scapula movements and limit the interpretation of the

resulting scapula motion.

Nonetheless, several researchers have identified decreased scapular upward rotation in both

healthy subjects and subjects with shoulder pathologies (Su, Johnson, Gravely, & Karduna,

2004; Warner, Micheli, Arslanian, Kennedy, & Kennedy, 1992; Lukaseiwicz, McClure,

Michener, Pratt, & Sennett, 1999). In addition, after shoulder complex fatigue, significant

changes in scapular position (decreased upward rotation, posterior tilting, and external rotation)

have been demonstrated using exercises that induced scapular and glenohumeral muscle fatigue

(Tsai, McClure, & Karduna, 2003). However, this previous research has focused on shoulder

external rotation fatigue and not on scapular musculature fatigue.

Lack of agreement in the findings are explained by the nature of measurements used, which

differ between static and dynamic movements, as well as instrumentation. One explanation for

these differences involves the muscles targeted for fatigue. For example, some studies have

examined shoulder complex fatigue due to a functional activity (Birkelo, Padua, Guskiewicz, &

Karas, 2003; Su, Johnson, Gravely, & Karduna, 2004; Madsen, Bak, Jensen, & Welter, 2011)

while others have compared a more isolated scapular-muscle fatigue protocol (McQuade,

Dawson, & Smidt, 1998; Suzuki, Swanik, Bliven, Kelly, & Swanik, 2006; Tyler, Cuoco,

Schachter, Thomas, & McHugh, 2009; Chopp, Fischer, & Dickerson, 2011), and others have

examined shoulder complex fatigue (Tsai, McClure, & Karduna, 2003; Joshi, Thigpen, Bunn,

Karas, & Padua, 2011; Noguchi, Chopp, Borgs, & Dickerson, 2013; Madsen, Bak, Jensen, &

Welter, 2011; Chopp, Fischer, & Dickerson, 2011). Therefore to date, no prior research has

specifically targeted the lower trapezius muscle using a therapeutic exercise with a maximal

activation pattern of the muscle.

2.2.1 Pathophysiology of scapula dyskinesis

Abnormal scapular motion and/or position have been collectively called “scapular winging”,

“scapular dyskinesia”, “altered scapula resting position”, and “scapular dyskinesis” (Table 2).

Table 2: Abnormal scapula motion terminology

Term Definition Possible Cause Static/Dynamic

scapular winging a visual abnormality of

prominence of the scapula

medial border

long thoracic nerve palsy

or overt scapular muscle

weakness

both

scapular

dyskinesia

loss of voluntary motion has

occurred only the scapular

translations

(elevation/depression and

retraction/protraction) can be

performed voluntarily,

whereas the scapular

rotations are accessory in

nature

adhesions, restricted range

of motion, nerve palsy

dynamic

scapular

dyskinesis

refers to movement of the

scapula that is dysfunctional

weakness/imbalance, nerve

injury and

acromioclavicular joint

injury, superior labral tears,

rotator cuff injury, clavicle

fractures, impingement

Dynamic

altered scapular

resting position

describing the static

appearance of the scapula

fractures, congenital

abnormality, SICK scapula

static

The most appropriate term to refer to dysfunctional dynamic movement of the scapula is the

term scapular dyskinesis (‘dys’—alteration of, ‘kinesis’—movement). When the arm is raised

overhead, the generally accepted pattern of scapulothoracic motion is upward rotation, external

rotation, and posterior tilt of the scapula as well as elevation and retraction of the clavicle

(Ludewig, et al., 1996; McClure, et al., 2001). Of the 14 muscles that attach to the scapula, the

trapezius and serratus anterior play a critical role in the production and control of scapulothoracic

motion (Ebaugh, et al., 2005; Inman, et al., 1944; Ludewig, et al., 1996). Furthermore, scapular

dyskinesis is reported to be more prominent as the arm is lowered from an overhead position and

individuals with shoulder pathology generally report more pain when lowering the arm (Kibler &

McMullen, 2003; Sharman, 2002).

Scapular dyskinesis has been identified by a group of experts as: (1) abnormal static scapular

position and/or dynamic scapular motion characterized by medial border prominence; or (2)

inferior angle prominence and/or early scapular elevation or shrugging on arm elevation; and/or

(3) rapid downward rotation during arm lowering (Kibler & Sciascia, 2010). Scapular

dyskinesis is a non-specific response to a painful condition in the shoulder rather than a specific

response to certain glenohumeral pathology and alters the scapulohumeral rhythm. Scapular

dyskinesis occurs when the upper trapezius, middle trapezius, lower trapezius, serratus anterior,

and latissimus dorsi (stabilizing muscles) are unable to preserve typical scapular movement

(Kibler & Sciascia, 2010). Scapula dyskinesis is potentially harmful when it results in increased

anterior tilting, downward rotation, and protraction, which reorients the acromion and decreases

the subacromial space width (Tsai, et al., 2003; Borstad, et al., 2009).

Alterations in static stabilizers (bone), muscle activation patterns, or strength in scapula

musculature have contributed to scapula dyskinesis. Researchers have shown that injuries to the

stabilizing ligaments of the acromioclavicular joint can cause the scapula to displace in a

downward, protracted, and internally rotated position (Kibler & Sciascia, 2010). With

displacement of the scapula, significant functional consequences to shoulder biomechanics occur

including an uncoupling of the scapulohumeral complex, inability of the scapular stabilizing

muscles to maintain appropriate positioning of the glenohumeral and acromiohumeral joints, and

a subsequent loss of rotator cuff strength and function (Joshi, Thigpen, Bunn, Karas, & Padua,

2011).

Scapular dyskinesis is associated with impingement by altering arm motion and scapula

position upon dynamic elevation, which is characterized by a loss of acromial upward rotation,

excessive scapular internal rotation, and excessive scapular anterior tilt (Cools, Struyf, De Mey,

Maenhout, Castelein, & Cagnie, 2013; Forthomme, Crielaard, & Croisier, 2008). These

associated alterations cause a decrease in the subacromial space and increase the individual’s

impingement risk.

Prior research has demonstrated altered activation sequencing patterns and strength of the

stabilizing muscles of the scapula in individuals diagnosed with impingement risk and scapular

dyskinesis (Cools, Struyf, De Mey, Maenhout, Castelein, & Cagnie, 2013; Kibler & Sciascia,

2010). Each scapula muscle makes a specific contribution to scapular function, but the lower

trapezius and serratus anterior appear to play the major role in stabilizing the scapula during arm

movement. Weakness, fatigue, or injury in either of these muscles may cause a disruption of the

dynamic stability, which leads to abnormal kinematics and symptoms of impingement. In a prior

study (Madsen, Bak, Jensen, & Welter, 2011), the authors demonstrated increased incidence of

scapula dyskinesis in pain-free competitive overhead athletes during increasing training and

fatigue. The prevalence of scapula dyskinesis seemed to increase with increased training to a

cumulative presence of 82% in pain-free competitive overhead athletes.

A classification system, which aids in clinical evaluation of scapula dyskinesis, has also been

reported in the literature (Kibler, Uhl, Maddux, Brooks, Zeller, & McMullen, 2002) and

modified to increase sensitivity (Uhl, Kibler, Gecewich, & Tripp, 2009). This method classifies

scapula dyskinesis based on the prominent part of the scapula and includes four types: 1) inferior

angle pattern (Type I), 2) medial border pattern (Type II), 3) superior border patters (Type III),

and 4) normal pattern (Type IV). The examiner first predicts if the individual has scapula

dyskinesis (yes/no method) then classifies the individual pattern type, which has a higher

sensitivity (76%) and positive predictive value (74%) than any other clinical dyskinesis measure

(Uhl, Kibler, Gecewich, & Tripp, 2009).

Increased upper trapezius activity, imbalance of upper trapezius/lower trapezius activation,

and decreased serratus anterior activity have been reported in patients with impingement (Cools,

Struyf, De Mey, Maenhout, Castelein, & Cagnie, 2013; Lawrence, Braman, Laprade, &

Ludewig, 2014). Authors have hypothesized that impingement due to lack of acromial elevation

is caused by increased upper trapezius activity (shrug maneuver) resulting in a type III (upper

medial border prominence) dyskinesis pattern (Kibler & Sciascia, 2010). Frequently, lower

trapezius activation is inhibited or is delayed (Cools, Struyf, De Mey, Maenhout, Castelein, &

Cagnie, 2013), which results in a type III/type II (entire medial border prominence) dyskinesis

pattern and impingement due to loss of acromial elevation and posterior tilt (Kibler & Sciascia,

2010).

Scapular position and kinematics influence rotator cuff strength (Kibler, Ludewig, McClure,

Michener, Bak, & Sciascia, 2013) and prior research (Kebaetse, McClure, & Pratt, 1999) has

demonstrated a 23% maximum rotator cuff strength decrease due to excessive scapular

protraction, a posture seen frequently in individuals with scapular dyskinesis. Another study

(Smith, Dietrich, Kotajarvi, & Kaufman, 2006) indicates that maximal rotator cuff strength is

achieved with a position of ‘neutral scapular protraction/retraction’ and the positions of

excessive protraction or retraction demonstrates decreased rotator cuff abduction strength.

Lastly, research has demonstrated (Kibler, Sciascia, & Dome, 2006) an increase of 24%

supraspinatus strength in a position of scapular retraction in individuals with shoulder pain and

11% increase in individuals without shoulder pain. The clinically observable finding in scapular

dyskinesis, prominence of the medial scapular border, is associated with the biomechanical

position of scapular internal rotation and protraction, which is a less than optimal base for muscle

strength (Kibler, & Sciascia, 2010).

Table 3: Causes of scapula dyskinesis

Cause Associated pathology

Bony thoracic kyphosis, clavicle fracture nonunion, clavicle shortened mal-union,

scapular fractures

Neurological cervical radiculopathy; long thoracic, dorsal scapular nerve, or spinal accessory

nerve palsy

Joint high grade AC instability, AC arthrosis, GH joint internal derangement (labral

injury), glenohumeral instability, biceps tendinitis

Soft Tissue inflexibility (tightness) or intrinsic muscle problems. Inflexibility and stiffness

of the pectoralis minor and biceps short head can create anterior tilt and

protraction due to their pull on the coracoid

soft tissue posterior shoulder inflexibility can lead to glenohumeral internal rotation

deficit (GIRD), shoulder rotation tightness (GIRD and Total Range of Motion

Deficit) and pectoralis minor inflexibility

Muscular periscapular muscle activation serratus anterior activation and strength is decreased

the upper trapezius/lower trapezius force couple may be altered delayed onset of

activation in the lower trapezius

lower trapezius and serratus anterior weakness, upper trapezius hyperactivity or

scapular muscle detachment and kinetic chain factors include hip/leg weakness and

core weakness

Causes of scapula dyskinesis remain multifactorial (Table 3), but altered scapular motion or

position decrease linear measures of the subacromial space (Giphart, van der Meijden, & Millett,

2012), increase impingement symptoms (Kibler, Ludewig, McClure, Michener, Bak, & Sciascia,

2013), decrease rotator cuff strength (Kebaetse, McClure, & Pratt, 1999; Smith, Dietrich,

Kotajarvi, & Kaufman, 2006; Kibler, Sciascia, & Dome, 2006) and increase the risk of internal

impingement (Kibler & Sciascia, 2010).

However, no conclusive study indicating the occurrence of scapular dyskinesis occurring as

a direct result of solely lower trapezius muscle fatigue, even though scapular orientation changes

in an impinging direction (downward rotation, anterior tilt, and protraction), have been reported

with fatigue (Birkelo, Padua, Guskiewicz, & Karas, 2003; Su, Johnson, Gravely, & Karduna,

2004; Madsen, Bak, Jensen, & Welter, 2011; McQuade, Dawson, & Smidt, 1998; Suzuki,

Swanik, Bliven, Kelly, & Swanik, 2006; Tyler, Cuoco, Schachter, Thomas, & McHugh, 2009;

Chopp, Fischer, & Dickerson, 2011; Tsai, McClure, & Karduna, 2003; Joshi, Thigpen, Bunn,

Karas, & Padua, 2011; Noguchi, Chopp, Borgs, & Dickerson, 2013; Madsen, Bak, Jensen, &

Welter, 2011; Chopp, Fischer, & Dickerson, 2011). Determining the effects of upper extremity

muscular fatigue and the associated mechanisms of subacromial space reduction is important

from a prevention and rehabilitation perspective. However, changes in scapular orientation

following targeted fatigue of scapular stabilizing lower trapezius muscles is currently unverified,

but one study (Borstad, Szucs, & Navalgund, 2009) used a ‘‘modified push-up plus’’ as a

fatiguing protocol, which elicited fatigue from the serratus anterior, upper and lower trapezius,

and the infraspinatus. The resulting kinematics from fatigue includes a decrease in posterior tilt

(-3.8˚), increase in internal rotation (protraction) (+3.2˚), and no change in upward rotation. The

prone rowing exercises, in which a patient lies prone on a bench and flexes the elbow from 0˚ to

90˚ while the shoulder flexion angle moves from 90˚ to 0˚ using a resistive weight, are clinically

recommended to strengthen the scapular stabilizers while minimally activating the rotator cuff

(Escamilla, et al., 2009; Reinold, et al., 2004). Research (Noguchi, Chopp, Borgs, & Dickerson,

2013) investigates the ability of this prone rowing task to solely target the scapular stabilizers in

order to help clarify whether scapular dyskinesis is a possible mechanism of fatigue-induced

subacromial impingement risk. However the authors (Noguchi, Chopp, Borgs, & Dickerson,

2013) showed no significant changes in 3-Dimensional scapula orientation. These results may

be due to the fact that the prone rowing exercise has a moderate to minimal EMG activation

profile of the lower trapezius (45±17%MVIC; Ekstrom, Donatelli, & Soderberg, 2003) and

(67±50%MVIC; Moseley, Jobe, Pink, Perry, & Tibone, 1992). Prone rowing has a maximal

activation of the upper trapezius (112±84%MVIC; Moseley, Jobe, Pink, Perry, & Tibone, 1992

and 63±17%MVIC; Ekstrom, Donatelli, & Soderberg, 2003), middle trapezius (59±51%MVIC;

Moseley, Jobe, Pink, Perry, & Tibone, 1992 and 79±23%MVIC; Ekstrom, Donatelli, &

Soderberg, 2003), and levator scapulae (117±69%MVIC; Moseley, Jobe, Pink, Perry, & Tibone,

1992). Therefore, it is difficult to demonstrate significant changes in scapular motion when the

primary scapular stabilizer (lower trapezius) isn’t specifically targeted in a fatiguing exercise.

Therefore, prone rowing or similar exertions intended to highly activate the scapular stabilizing

muscles, while minimally activating the rotator cuff, failed to do so, suggesting that the correct

muscle which contributes to maintain healthy glenohumeral and scapulothoracic kinematics was

not targeted.

2.3 LIMITATIONS OF STUDYING EMG ON SHOULDER MUSCLES

Abnormal muscle activity patterns have been observed in overhead athletes with

impingement (Lukaseiwicz, McClure, Michener, Pratt, & Sennett, 1999; Ekstrom, Donatelli, &

Soderberg, 2003; Ludewig, & Cook, 2000) and electromyography (EMG) analysis is used to

assess muscle activity in the shoulder (Kelly, Backus, Warren, & Williams, 2002). Fine wire

(fw) EMG and surface (s) EMG have been used to demonstrate changes in muscle activity

(Jaggi, et al., 2009) and the study of muscle function through EMG helps quantify muscle

activity by recording the electrical activity of the muscle (Solomonow, et al., 1994). In general,

the electrical activity of an individual muscle’s motor unit is measured and therefore the more

active the motor units the greater the electrical activity. The choice of electrode type is typically

determined by the size and site of the muscle being investigated with fwEMG used for deep

muscles and sEMG used for superficial muscles (Jaggi, et al., 2009). It is also important to note

that it can be difficult to test in the exact same area for fwEMG and sEMG, since they are both

attached to the skin and the skin can move above the muscle.

Jaggi (Jaggi, et al., 2009) examined the level of agreement in sEMG and fwEMG in the

infraspinatus, pectoralis major, latissimus dorsi, and anterior deltoid of 18 subjects with a

diagnosis of shoulder instability. While this study didn’t have a control, the sEMG and fwEMG

demonstrated a poor level of agreement but the sensitivity and specificity for the infraspinatus

was good (Jaggi, et al., 2009). However, this article demonstrated poor power, a lack of a

control group, and a possible investigator bias. In this article, two different investigators

performed the five identical uniplanar movements, but at different times the individual

investigator bias may have affected levels of agreement in this study. Also, the diagnosis of

shoulder instability is a multifactorial diagnosis which may or may not include pain and which

may also contain a secondary pathology like a RTC tear, labral tear, shoulder impingement, and

numerous types of instability (including anterior, inferior, posterior, and superior instability).

In a study by Meskers and colleagues (Meskers, de Groot, Arwert, Rozendaal, &

Rozing, 2004), 12 subjects without shoulder pathology underwent sEMG and fwEMG testing of

12 shoulder muscles while performing various movements of the upper extremity. Also, some

subjects were retested again at days 7 and 14 and this method demonstrated sufficient accuracy

for intra-individual measurements on different days. Therefore, this article gives some support

to the use of EMG testing of shoulder musculature before and after interventions.

In general, sEMG may be more representative of the overall activity of a given muscle,

but a disadvantage to this is that some of the measured electrical activity may originate from

other muscles not being studied, a phenomenon called crosstalk (Solomonow, et al., 1994).

Generally, sEMG may pick up 5-15% electrical activity from surrounding muscles not being

studied and subcutaneous fat may also influence crosstalk in sEMG amplitudes (Solomonow, et

al., 1994; Jaggi, et al., 2009). Inconsistencies in sEMG interpretations arise from differences in

subcutaneous fat layers, familiarity with test exercise, actual individual strain level during

movement, or other physiological factors.

Methodological inconsistencies of EMG testing include accuracy of skin preparation,

distance between electrodes, electrode localization, electrode type and orientation, and

normalization methods. The standard for EMG normalization is the calculation of relative

amplitudes, which is referred to as maximum voluntary contraction level (MVC) (Anders,

Bretschneider, Bernsdorf, & Schneider, 2005). However, some studies have shown non-linear

amplitudes due to recruitment strategies and the speed of contraction (Anders, Bretschneider,

Bernsdorf, & Schneider, 2005).

Maximum voluntary isometric contraction (MVIC) has also been used in normalization

of EMG data. Knutson et al. (Knutson, Soderberg, Ballantyne, & Clarke, 2005) found that

MVIC method of normalization demonstrates lower variability and higher inter-individual

reliability compared to MVC of dynamic contractions. The overall conclusion was that MVIC

was the standard for normalization in the normal and orthopedically impaired population. When

comparing EMG between subjects, EMG is normalized to MVIC (Ekstrom, Soderberg, &

Donatelli, 2005).

When testing EMG on healthy and orthopedically impaired overhead athletes, muscle

length, bone position, and muscle contraction can all add variance to final observed measures.

Intra-individual errors between movements and between groups (healthy vs pathologic) and

intra-observer variance can also add variance to the results. Pain in the pathologic population

may not allow the individual to perform certain movements, which is a limitation specific to this

population. Also, MVIC testing is a static test, which may be used for dynamic testing but allows

for between subject comparisons. Kelly and colleagues (Kelly, Backus, Warren, & Williams,

2002) have described 3 progressive levels of EMG activity in shoulder patients. The authors

suggested that a minimal reading was between 0-39% MVIC, a moderate reading was between

40-74% MVIC, and a maximal reading was between 75-100% MVIC.

When dealing with recording EMG while performing therapeutic exercise, changing

muscle length and the speed of contraction is an issue that should be addressed since it may

influence the magnitude of the EMG signal (Ekstrom, Donatelli, & Soderberg, 2003). This can

be addressed by controlling the speed by which the movement is performed since it has been

demonstrated that a near linear relationship exists between force production and EMG recording

in concentric and eccentric contractions with a constant velocity (Ekstrom, Donatelli, &

Soderberg, 2003). The use of a metronome has been used in prior studies to address the velocity

of movements and keep a constant rate of speed.

2.4 SHOULDER AND SCAPULA DYNAMICS

Shoulder dynamics result from the interplay of complex muscular, osseous, and

supporting structures, which provide a range of motion that exceeds that of any other joint in the

body and maintain proper control and stability of all involved joints. The glenohumeral joint

resting position and its supporting structures static alignment are influenced by static thoracic

spine alignment, humeral bone components, scapular bone components, clavicular bony

components, and the muscular attachments from the thoracic and cervical spine (Wilk, Reinold,

& Andrews, 2009).

Alterations in shoulder range of motion (ROM) have been associated with shoulder

impingement along with scapular dyskinesis, (Lukaseiwicz, McClure, Michener, Pratt, Sennett,

1999; Ludewig & Cook, 2000; Endo, Ikata, Katoh, & Takeda, 2001) clavicular movement, and

increased humeral head translations (Ludewig & Cook, 2002; Laudner, Myers, Pasquale,

Bradley, & Lephart, 2006; McClure, Michener, & Karduna, 2006; Warner, Micheli, Arslanian,

Kennedy, & Kennedy, 1992; Deutsch, Altchek, Schwartz, Otis, & Warren, 1996; Lin, et al.,

2005). All of these deviations are believed to reduce the subacromial space or approximate the

tendon undersurface to the glenoid labrum, creating decreased clearance of the RTC tendons and

other structures under the acromion (Graichen, et al., 1999). These altered shoulder kinematics

cause alterations in shoulder and scapular muscle activation patterns or altered resting length of

shoulder muscles.

2.4.1 Shoulder/scapular movements

Normal shoulder biomechanics have been studied with EMG during ROM (Ludewig &

Cook, 2000; Kibler & McMullen, 2003; Bagg & Forrest, 1986), cadaver studies (Johnson,

Bogduk, Nowitzke, & House, 1994), patients with nerve injuries (Brunnstrom, 1941; Wiater &

Bigliani, 1999), and in predictive biomechanical modeling of the arm and muscular function

(Johnson, Bogduk, Nowitzke, & House, 1994; Poppen & Walker, 1978). These approaches have

refined our knowledge about the function and movements of the shoulder and scapula

musculature. Understanding muscle adaptation to pathology in the shoulder is important for

developing guidelines for interventions to improve shoulder function. These studies have

defined a general consensus on what muscles will be active and when during normal shoulder

range of motion.

In 1944 Inman (Inman, Saunders, & Abbott, 1944) discussed the “scapulohumeral

rhythm”, which is a ratio of “2:1” glenohumeral joint to scapulothoracic joint range of motion

during active range of motion. Therefore, if the glenohumeral joint moves 180 degrees of

abduction then the scapula rotates 90 degrees. However, this ratio doesn’t account for the

different planes of motion, speed of motion, or loaded movements and therefore this 2:1 ratio has

been debated in the literature with numerous recent authors reporting various scapulohumeral

ratios (Table 4) from 2.2:1 to 1.7:1 with some reporting even larger ratios of 3:2 (Freedman &

Munro, 1966) and 5:4 (Poppen & Walker, 1976). Many of these discrepancies may be due to

different measuring techniques and different methodologies in the studies. McQuade and

Table 4: Scapulohumeral ratio during shoulder elevation

Study Year Scapulohumeral ratio

Fung et al. 2001 2.1/1

Ludewig et al. 2009 2.2/1

McClure et al. 2001 1.7/1

Inman et al. 1944 2:1

Freedman & Monro 1966 3:2

Poppen & Walker 1976 1.24:1 or 5:4

McQuade & Smidt 1998 7.9:1 to 2.1:1 (PROM) 1.9:1 to 4.5:1

(loaded)

colleagues (McQuade & Smidt, 1998) also reported that that the 2:1 ratio doesn’t adequately

explain normal shoulder kinematics. However, McQuade and colleagues didn’t look at

submaximal loaded conditions, a pathological population, EMG activity during the test, but

rather looked at only the concentric phase which will all limit the clinical application of the

research results.

There is also disagreement as to when this 2:1 scapulohumeral ratio occurs even though it

is generally considered to occur in 60 to 120 degrees with 1 degree of scapular movement

occurring for every 2 degrees of elevation movement until 120 degrees and thereafter 1 degree of

scapular movement for every 1 degrees of elevation movement (Reinold, Escamilla, & Wilk,

2009). Contrary to general considerations some authors have noted the greatest scapular

movement at 30 to 60 degrees while others have found the greatest movement at 80 to 140

degrees, but generally these discrepancies are due to different measuring techniques (Bagg &

Forrest, 1986).

Normal scapular movement during glenohumeral elevation helps maintain correct length

tension relationships of the shoulder musculature and prevent the subacromial structures from

being impinged and generally includes upward rotation, external rotation, and posterior tilting on

the thorax with upward rotation being the dominant motion (McClure, et al., 2001; Ludewig &

Reynolds, 2009). Overhead athletes generally exhibit increased scapular upward rotation,

internal rotation, and retraction during elevation and this is hypothesized to be an adaptation to

allow for clearance of subacromial structures during throwing (Wilk, Reinold, & Andrews,

2009). Generally accepted normal ranges have been observed for scapular upward rotation (45-

55 degrees), posterior tilting (20-40 degrees), and external rotation (15-35 degrees) during

elevation and the scapular muscles are vitally important in maintaining the scapulohumeral

kinematic balance since they cause scapular movements (Wilk, Reinold, & Andrews, 2009;

Ludewig & Reynolds, 2009).

However, the amount of scapular internal rotation during elevation has shown a great

deal of variability across investigations, elevation planes, subjects, and points in the

glenohumeral range of motion. Authors suggest that a slight increase in scapular internal

rotation may be normal early in glenohumeral elevation (McClure, Michener, Sennett, &

Karduna, 2001) and it is also generally accepted (but has limited evidence to support) that end

range elevation involves scapular external rotation (Ludewig & Reynolds, 2009).

Scapulothoracic “translations” (Figure 2) also occur during arm elevation and include

elevation/depression and adduction/abduction (retraction/protraction), which are derived from

clavicular movements. Also scapulothoracic kinematics involve combined acromioclavicular

(AC) and sternoclavicular (SC) joint motions, therefore, authors have performed studies of the 3-

dimensional motion analysis of the AC and SC joints in healthy subjects and have linked

scapulothoracic elevation to SC elevation and scapulothoracic abduction/adduction to SC

protraction/retraction (Ludewig & Reynolds, 2009).

Figure 2: Scapulothoracic translations during arm elevation

Despite these numerous scapular movements, there remain gaps in the literature and

unanswered questions including: 1) which muscles are responsible for internal/external rotation

or anterior/posterior tilting of the scapula, 2) what are normal values for protraction/retraction 3)

what are normal values for scapulothoracic elevation/depression, 4) how do we measure

scapulothoracic “translations”?

2.4.2 Loaded vs unloaded

The effect of an external load in the hand during elevation remains unclear on scapular

mechanics, scapulohumeral ratio, and EMG activity of the scapular musculature. Adding a .5kg

load in the hand while performing shoulder movements has been shown to increase the EMG

activity of the shoulder musculature. In a study of 16 subjects by Antony and Keir (Antony &

Keir, 2010), subjects performed scaption with a .5kg load added to the hand and shoulder

maximum voluntary excitation (MVE) increased by 4% across all postures and velocities. Also,

when the subjects use a firmer grip on the load a decrease of 2% was demonstrated in the

anterior and middle deltoid, and increase of 2% was seen in the posterior deltoid infraspinatus

and trapezius, and lastly the biceps increased by 6% MVE. While this study gives some

evidence for the use of a loaded exercise with a firmer grip on dumbbells while performing

rehabilitation, the study had limited participants and was only performed on a young and healthy

population which limits clinical application of the results.

Some researchers have shown no change in scapulothoracic ratio with the addition of

resistance (Freedman & Munro, 1966), while others reported different ratios with addition of

resistance (McQuade & Smidt, 1998). However, several limitations are noted in the McQuade &

Smidt study including: 1) submaximal loads were not investigated; 2) pathological population

not assessed; 3) EMG analysis was not performed; and 4) only concentric movements were

investigated. All of these shortcomings limit the study’s results to a pathological population and

more research is needed on the effect of loads on the scapulohumeral ratio.

Witt and colleagues (Witt, Talbott, & Kotowski, 2011) examined upper, middle, and

lower trapezius, and serratus anterior EMG activity with a 3 pound dumbbell weight and elastic

resistance during diagonal patterns of movement in 21 healthy participants. They concluded that

the type of resistance didn’t significantly change muscle activity in the diagonal patterns tested.

However, this study did demonstrate limitations which will alter interpretation including: 1) the

study population’s exercise/fitness level was not determined; 2) the resistance selection

procedure didn’t use any form of repetition maximum percentage; and 3) there may have been

crosstalk with the sEMG selection.

2.4.3 Scapular plane vs. other planes

The scapular plane is located 30 to 40 degrees anterior to the coronal plane, which offers

biomechanical and anatomical features. In the scapular plane elevation the joint surfaces have

greater conformity, the inferior shoulder capsule ligaments and RTC tendons remain untwisted,

and the supraspinatus and deltoid are advantageously aligned for elevation than flexion and/or

abduction (Dvir & Berme, 1978). Besides these advantages, the scapular plane is where most

functional activities are performed and is also the optimal plane for shoulder strengthening

exercises. While performing strengthening exercises in the scapular plane, shoulder

rehabilitation is enhanced since unwanted passive tension on the RTC tendons and the

glenohumeral joint capsule are at its lowest point and much lower than in flexion and/or

abduction (Wilk, Reinold, & Andrews, 2009). Scapular upward rotation is also greater in the

scapular plane, which will decrease during elevation, but will allow for more “clearance in the

subacromial space” and decrease the risk of impingement.

2.4.4 Scapulothoracic EMG activity

Previous studies have also examined scapulothoracic EMG activity and kinematics

simultaneously to relate the functional status of muscle with scapular mechanics. In general

during normal shoulder elevation, the scapula will upwardly rotate and posteriorly tilt on the

thorax. Scapula internal rotation has also been studied but shows variability across investigations

(Ludwig & Reynolds, 2009).

A general consensus has been established regarding the role of the scapular muscles

during arm movements even with various approaches (different positioning of electrodes on

muscles during EMG analysis [Ludwig & Cook, 2000; Lin, et al. 2005; Ekstrom, Bifulco,

Lopau, Andersen, & Gough, 2004)], different normalization techniques (McLean, Chislett,

Keith, Murphy, & Walton, 2003; Ekstrom, Soderberg, & Donatelli, 2005), varying velocity of

contraction, various types of contraction, and various muscle length during contraction. Though

EMG activity doesn’t specify if a muscle is stabilizing, translating or rotating a joint, it does

demonstrate how active a muscle is during a movement. Even with these various approaches and

confounding factors, it is generally understood that the trapezius and serratus anterior (middle

and lower) can stabilize and rotate the scapula (Bagg & Forrest, 1986; Johnson, Bogduk,

Nowitzke, & House, 1994; Brunnstrom, 1941; Ekstrom, Bifulco, Lopau, Andersen, Gough,

2004; Inman, Saunders, & Abbott, 1944). Also during arm elevation the scapulothoracic

muscles produce upward rotation and resist downward rotation acting on the scapula (Dvir &

Berme, 1978). Three muscles including the trapezius (upper, middle, and lower), the pectoralis

minor, and the serratus anterior (middle, lower, and superior) have been observed using EMG

analysis.

In prior studies, the trapezius has been responsible for stabilizing the scapula since the

middle and lower fibers are perfectly aligned to produce scapula external rotation facilitating

scapular stabilization (Johnson, Bogduk, Nowitzke, & House, 1994). Also, the trapezius is more

active during abduction versus flexion (Inman, Saunders, & Abbott, 1944; Wiedenbauer &

Mortensen, 1952) due to decreased internal rotation of the scapula in scapular plane abduction.

The upper trapezius is most active with scapular elevation and is produced through clavicular

elevation. The lower trapezius is the only part of the trapezius that can upwardly rotate the

scapula while the middle and lower trapezius are ideally suited for scapular stabilization and

external rotation of the scapula.

Another important muscle is the serratus anterior which can be broken into upper,

middle, and lower groups. The middle and lower serratus anterior fibers are oriented in such a

way that they are at a substantial mechanical advantage for scapular upward rotation (Dvir &

Berme, 1978) in combination with the ability to posterior tilt and externally rotate the scapula.

Therefore, the middle and lower serratus anterior are the primary movers for scapular rotation

during arm elevation and they are the only muscles that can posteriorly tilt the scapula on the

thorax. Lastly, the upper serratus has been minimally investigated (Ekstrom, Bifulco, Lopau,

Andersen, Gough, 2004).

The pectoralis minor can produce scapular downward rotation, internal rotation, and

anterior tilting (Borstad & Ludewig, 2005) opposing upward rotation and posterior tilting during

arm elevation (McClure, Michener, Sennett, & Karduna, 2001). Prior studies (Borstad &

Ludewig, 2005) have demonstrated that decreased length of the pectoralis minor decreases the

posterior tilt and increases the internal rotation during arm elevation which increases

impingement risk.

2.4.5 Glenohumeral EMG activity

Besides the scapulothoracic musculature, the glenohumeral musculature including the

deltoid and rotator cuff (supraspinatus, infraspinatus, subscapularis, and teres minor) are

contributors to proper shoulder function. The deltoid is the primary mover in elevation and it is

assisted by the supraspinatus initially (Sharkey, Marder, & Hanson, 1994). The rotator cuff

stabilizes the glenohumeral joint against excessive humeral head translations through a medially

directed compression of the humeral head into the glenoid (Sharkey & Marder, 1995). The

subscapularis, infraspinatus, and teres minor have an inferiorly directed line of action offsetting

the superior translation component of the deltoid muscle (Sharkey, Marder, & Hanson, 1994).

Therefore, proper balance between increasing and decreasing forces results in (1-2mm) superior

translation of humeral head during elevation. Finally, the infraspinatus and teres minor produce

humeral head external rotation during arm elevation.

2.4.6 Shoulder EMG activity with impingement

Besides experiencing pain and other deficits, decreased EMG activation of numerous muscles

has been observed in patients with shoulder impingement. In patients with shoulder

impingement, a decrease in overall serratus anterior activity from 70 to 100 degrees and a

decrease activation of lower serratus anterior from 31 to 120 degrees in scapular plane arm

elevation (Ludwig & Cook, 2000). The upper trapezius has also shown decreased activity

between 40 to 100 degrees and increased activity of the upper and lower trapezius from 61-120

degrees while performing scaption loaded (Ludwig & Cook, 2000; Peat & Grahame, 1977).

Increased upper trap activation is consistent (Ludwig & Cook, 2000; Peat & Grahame, 1977) and

associated with increased clavicular elevation or scapular elevation found in studies (McClure,

Michener, & Karduna, 2006; Kibler & McMullen, 2003). This increased clavicular elevation at

the SC joint may be produced by increased upper trapezius activity (Johnson, Bogduk,

Nowitzke, & House, 1994)

and results in scapular anterior tilting causing a potential mechanism

to cause or aggravate impingement symptoms. In conclusion, middle and lower serratus

weakness or decreased activity contributes to impingement syndrome. Increasing function of this

muscle may alleviate pain and dysfunction in shoulder impingement patients.

Alterations in rotator cuff muscle activation have been seen in patients with

impingement. Decreased activity of the deltoid and rotator cuff is not pronounced in early areas

of motion (Reddy, Mohr, Pink, & Jobe, 2000). However, the infraspinatus, supraspinatus, and

middle deltoid demonstrate decreased activity from 30-60 degrees, decreased infraspinatus

activity from 60-90 degrees, and no significant difference was seen from 90-120 degrees. This

decreased activity is theorized to be related to inadequate humeral head depression (Reddy,

Mohr, Pink, & Jobe, 2000). Another study demonstrated that impingement decreased activity of

the subscapularus, supraspinatus, and infraspinatus; increased middle deltoid activation from 0-

30 degrees; decreased coactivation of the supraspinatus and infraspinatus from 30-60 degrees;

and increased activation of the infraspinatus, subscapularis, and supraspinatus from 90-120

degrees (Myers, Hwang, Pasquale, Blackburn & Lephart, 2008). Overall, impingement caused

decreased RTC coactivation and increased deltoid activity at the initiation of elevation (Reddy,

Mohr, Pink, & Jobe, 2000; Myers, Hwang, Pasquale, Blackburn, & Lephart, 2008).

2.4.7 Normal shoulder EMG activity

Normal Shoulder EMG activity will allow for proper shoulder function and maintain

adequate clearance of the subacromial structures during shoulder function and elevation (Table

5). The scapulohumeral muscles are vitally important to provide motion, provide dynamic

stabilization, and provide proper coordination and sequencing in the glenohumeral complex of

overhead athletes due to the complexity and motion needed in overhead sports. Since the

glenohumeral and scapulothoracic joints are attached by musculature, the muscular activity of

the shoulder complex musculature can be correlated to the maintenance of the scapulothoracic

rhythm and maintenance of the shoulder force couples including: 1) Deltoid-rotator cuff; 2)

Upper trapezius and serratus anterior; and 3) anterior posterior rotator cuff.

Table 5: Mean glenohumeral EMG normalized by MVIC during scaption with neutral rotation

(Adapted from Alpert, Pink, Jobe, McMahon, & Mathiyakom, 2000).

Interval Anterior

Deltoid

EMG

Middle

Deltoid

EMG

Posterior

Deltoid

EMG

Supraspin

atus EMG

(%MVIC)

Infraspina

tus EMG

(%MVIC)

Teres

Minor

EMG

(%MVIC)

Subscapul

aris EMG

(%MVIC)

(%MVIC (%MVIC) (%MVIC)

)

0-30˚ 22±10 30±18 2±2 36±21 16±7 9±9 6±7

30-60˚ 53±22 60±27 2±3 49±25 34±14 11±10 14±13

60-90˚ 68±24 69±29 2±3 47±19 37±15 15±14 18±15

90-120˚ 78±27 74±33 2±3 42±14 39±20 19±17 21±19

120-150˚ 90±31 77±35 4±4 40±20 39±29 25±25 23±19

During initial arm elevation the more powerful deltoid exerts an upward and outward

force on the humerus. If this force would occur unopposed then superior migration of the

humerus would occur and result in impingement and a 60% pressure increase of the structures

between the greater tuberosity and the acromion when the rotator cuff is not working properly

(Ludewig & Cook, 2002). While the direction of the RTC force vector is debated to be parallel

to the axillary border (Inman, et al., 1944) or perpendicular to the glenoid (Poppen & Walker,

1978), the overall effect is a force vector which counteracts the deltoid.

In normal healthy shoulders, Matsuki and colleagues (Matsuki, et al., 2012) demonstrated

2.1mm of average humeral head superior migration from 0-105˚ of elevation and a .9mm

average inferior translation from 105-180˚ in elevation during fluoroscopic images of the

shoulder of 12 male subjects. The deltoid-rotator cuff force couple exists when the deltoids

superior directed force is counteracted by an inferior and medially directed force from the

infraspinatus, subscapularis, and teres minor. The supraspinatus also exerts a compressive force

on the humerus onto the glenoid, therefore serving an approximating role in the force couple

(Inman, Saunders, & Abbott, 1944). This RTC helps neutralize the upward shear force, reduces

workload on the deltoid through improving mechanical advantage (Sharkey, Marder, & Hanson,

1994), and assists in stabilization. Previous authors have also demonstrated that RTC fatigue or

tears will increase superior migration of the humeral head (Yamaguchi, et al., 2000)

demonstrating the importance of a correctly functioning force couple.

A second force couple, a synergistic relation between the upper trapezius and serratus

anterior, exists to produce upward rotation of the scapula during shoulder elevation and servers

4 functions: 1) allows for rotation of the scapula, maintaining the glenoid surface for optimal

positioning; 2) maintains efficient length tension relationship for the deltoid; 3) prevents

impingement of the rotator cuff from the subacromial structures; and 4) provides a stable

scapular base enabling appropriate recruitment of the scapulothoracic muscles. The

instantaneous center of rotation starts near the medial border of the scapular spine at lower

levels of elevation and therefore the lower trapezius has a small lever arm due to its distal

attachment being near the center of rotation. However during continued elevation the

instantaneous center of rotation moves laterally along the spine toward the acromioclavicular

joint and therefore at higher levels of abduction (≥90˚) the lower trapezius will have a larger

lever arm and a greater

influence on upward rotation and scapular stabilization, along with the serratus anterior (Bagg &

Forrest, 1988).

Overall, the position of the scapula is important to center the humeral head on the glenoid

creating a stable foundation for shoulder movements in overhead athletes (Ludwig & Reynolds,

2009). In healthy shoulders, the force couple between the serratus anterior and the trapezius

rotates the scapula whereby maintaining the glenoid surface in an optimal position, positions the

deltoid muscle in an optimal length tension relationship, and provides a stable foundation (Wilk,

Reinold, & Andrews, 2009). A correctly functioning force couple will prevent impingement of

the subacromial structures on the coracoacromial arch and enable the deltoid and scapulothoracic

muscles to generate more power, stability, and force (Wilk, Reinold, & Andrews, 2009). A

muscle imbalance from weakness or shortening can result in an alteration of this force couple,

whereby contributing to impaired shoulder stabilization and possibly leading to impingement.

The anterior-posterior RTC force couple creates inferior dynamic stability (depressing the

humeral head) and a concavity-compression mechanism (compress humeral head in glenoid) due

to the relationship between the anterior-based subscapularis and the posterior-based teres minor

and infraspinatus. Imbalances have been demonstrated in overhead athletes due to overdeveloped

internal rotators and underdeveloped external rotators in the shoulder.

2.4.8 Abnormal scapulothoracic EMG activity

While no significant change has been noted in resting scapular position of the

impingement population (Ludewig & Cook, 2000; Lukaseiwicz, McClure, Michener, Pratt, &

Sennett, 1999) alterations of scapular upward rotation, posterior tilting, clavicular

elevation/retraction, scapular internal rotation, scapular symmetry, and scapulohumeral rhythm

have been observed (Ludewig & Reynolds, 2009; Lukasiewicz, McClure, Michener, Pratt, &

Sennett, 1999; Ludewig & Cook, 2000; McClure, Michener, & Karduna, 2006; Endo, Ikata,

Katoh, & Takeda, 2001). Overhead athletes have also demonstrated a relationship between

scapulothoracic muscle imbalance and altered scapular muscle activity has been associated with

SIS (Reinold, Escamilla, & Wilk, 2009).

SAS has been linked with altered kinematics of the scapula while elevating the arm called

scapular dyskinesis, which is defined as observable alterations in the position of the scapula and

the patterns of scapular motion in relation to the thoracic cage. JP Warner coined the term

scapular dyskinesis and Ben Kibler described a classification system which outlined 3 primary

scapular dysfunctions which names the condition based on the portion of the scapula most

pronounced or most presently visible when viewed during clinical examination.

Burkhart and colleagues (Burkhart, Morgan, & Kibler, 2003) also coined the term SICK

(Scapular malposition, Inferior medial border prominence, Coracoid pain and malposition, and

dyskinesis of scapular movement) scapula to describe an asymmetrical malposition of the

scapula in throwing athletes.

In normal healthy arm elevation, the scapula will upwardly rotate, posteriorly tilt, and

externally rotate and numerous authors have studied the alterations in scapular movements with

SAS (Table 6). The current literature is conflicting in regard to the specific deviations of

scapular motion in the SAS population. Researchers have reported a decrease in posterior tilt in

the SAS population (Lukasiewicz, McClure, Michener, Pratt, & Sennett, 1999; Ludewig &

Cook, 2000, 2002; Endo, Ikata, Katoh, & Takeda, 2001; Lin, Hanten, Olson, Roddey, Soto-

quijano, Lim, et al., 2005) while others have demonstrated an increase (McClure, Michener, &

Karduna, 2006; McClure, Michener, Sennett, & Karduna, 2001; Laudner, Myers, Pasquale,

Bradley, & Lephart, 2006) or no difference (Hebert, Moffet, McFadyen, & Dionne, 2002).

Table 6: Scapular movement differences during shoulder elevation in healthy controls and the impingement population

Study Method Sample Upward

rotation

Posterior tilt External

rotation

internal

rotation

Interval (˚)/

plane

Comments

Lukasiewi

cz et al.

(1999)

Electromec

hanical

digitizer

20 controls

17 SIS

difference

↓ at 90° and

max elevation

difference

?0-max /

scapular

25-66 y.o. male

and female

Ludewig

& Cook

(2000)

sEMG 26 controls

26 SIS

↓ at 60°

elevation

↓ at 120°

elevation

↓ when

loaded

? 0-120 /

scapular

20-71 y.o. males

only, overhead

workers

McClure

et al.

(2006)

sEMG 45 controls

45 SIS

↑ at 90°

and 120°

in sagittal

plane

↑ at 120° in

scapular plane

difference

?0-max /

scapular and

sagittal

24-74 y.o. male

and female

Endo et

al. (2001)

Static

radiographs

27 SIS

bilateral

comparison

↓ at 90°

elevation

↓ at 45° and

90° elevation

difference

? 0-90 /

frontal

41-73 y.o. male

and female

Graichen

et al.

(2001)

Static MRI 14 controls

20 SIS

significant

difference

? ? ? 0-120 /

frontal

22-62 y.o. male

female

Hebert et

al. (2002)

calculated

with optical

surface

sensors

10 controls

41 SIS

significant

difference

No significant

differences

?↑ on side

with SIS

0-110 /

frontal and

coronal

30-60 y.o. both

genders, used

bilateral

shoulders

Lin et al.

(2005)

sEMG 25 controls,

21 shoulder

dysfunction

↓ in SD

group

↓ in SD group ? No

significant

differences

Approximat

e 0-120 /

scapular

plane

Males only, 27-

82 y.o.

Laudner

et al.

(2006)

sEMG 11 controls

11 internal

impingement

significant

difference

↑ in

impingement

? No

significant

differences

0-120 /

scapular

plane

Males only,

throwers, 18-30

y.o.

Similarly, Researchers have reported a decrease in upward rotation in the SAS

population (Ludewig & Cook, 2000, 2002; Endo, Ikata, Katoh, & Takeda, 2001; Lin, Hanten,

Olson, Roddey, Soto-quijano, Lim, et al., 2005) while others have demonstrated an increase

(McClure, Michener, & Karduna, 2006) or no difference (Lukasiewicz, McClure, Michener,

Pratt, & Sennett, 1999; Hebert, Moffet, McFadyen, & Dionne, 2002; Laudner, Myers, Pasquale,

Bradley, & Lephart, 2006; Graichen, Stammberger, Bone, Wiedemann, Englmeier, Reiser, &

Eckstein, 2001). Lastly, researchers have also reported a decrease in external rotation during

weighted elevation (Ludewig & Cook, 2000) while other have shown no difference during

unweighted elevation (Lukasiewicz, McClure, Michener, Pratt, & Sennett, 1999; Endo, Ikata,

Katoh, & Takeda, 2001; McClure, Michener, Sennett, & Karduna, 2001). One study has

reported an increase internal rotation (Hebert, Moffet, McFadyen, & Dionne, 2002) while

others have shown no differences (Lin, Hanten, Olson, Roddey, Soto-quijano, Lim, et al., 2005;

Laudner, Myers, Pasquale, Bradley, & Lephart, 2006) or reported a decrease (Ludewig & Cook,

2000). However with all these deviations and differences, researches seem to agree that athletes

with SIS have decreased upward rotation during elevation (Ludewig & Cook, 2000, 2002;

Endo, Ikata, Katoh, & Takeda, 2001; Lin, Hanten, Olson, Roddey, Soto-quijano, Lim, et al.,

2005) with exception of one study (McClure, Michener, & Karduna, 2006).

These conflicting results in the scapular motion literature are likely due to the smaller

measurements of scapular tilt and internal/external rotation (25˚-30˚) when compared to

scapular upward rotation (50˚), the altered scapular kinematics related to a specific type of

impingement, the specific muscular contributions to anterior/posterior tilting and

internal/external rotation are unclear, and/or the lack of valid scapular motion measurement

techniques in anterior/posterior tilting and internal/external rotation compared to upward

rotation.

The scapular muscles have also exhibited altered muscle activation patterns during

elevation in the impingement population including increased activation of the upper trapezius

and decreased activation of the middle/lower trapezius and serratus anterior (Cools et al., 2007;

Cools, Witvrouw, Declercq, Danneels, & Cambier, 2003; Wadsworth & Bullock-Saxton, 1997).

In contrast Ludewig & Cook (Ludewig & Cook, 2000), demonstrated increased activation in

both the upper and lower trapezius in SIS when compared to a control, and Lin and colleagues

(Lin, et al., 2005) demonstrated no change in lower trapezius activity. These different results

make the final EMG assessment unclear in the impingement population, however there are some

possible explanation for the differences in results including: 1) Ludewig & Cook performed

there experiment weighted in male and female construction workers, 2) Lin and colleagues

performed their experiment with numerous shoulder pathologies and in males only, 3) Cools and

colleagues used maximal isokinetic testing in abduction in overhead athletes, and 4) all of these

studies demonstrated large age ranges in their populations.

However, there is a lack of reliable studies in the literature pertaining to the EMG

activity changes in overhead throwers with SIS after injury/pre-rehabilitation and after injury

post- rehabilitation. The inability to detect significant differences between groups by

investigators is primarily due to limited sample sizes, limited statistical power for some

comparisons, the large variation in the healthy population, sEMG signals in studies is altered by

skin motion, and limited static imaging in supine.

2.4.9 Abnormal glenohumeral/rotator cuff EMG activity

Abnormal muscle patterns in the deltoid-rotator cuff and/or anterior posterior rotator cuff

force couple can contribute to SIS and have been demonstrated in the impingement population

(Myers, Hwang, Pasquale, Blackburn, & Lephart, 2008; Reddy, Mohr, Pink, & Jobe, 2000). In

general, researchers have found decreased deltoid activity (Reddy, Mohr, Pink, & Jobe, 2000),

deltoid atrophy (Leivseth & Reikeras, 1994), and decreased rotator cuff activity (Reddy, Mohr,

Pink, & Jobe, 2000) which can lead to decreased stabilization, unopposed deltoid activity, and

induce compression of subacromial structures causing a 1.7mm-2.1mm humeral head

anteriosuperior migration during 60˚-90˚ of abduction (Sharkey, Marder, & Hanson, 1994). The

impingement population has demonstrated decreased infraspinatus and subscapularis EMG

activity from 30˚-90˚ elevation when compared to a control (Reddy, Mohr, Pink, & Jobe, 2000).

Myers and colleagues (Myers, Hwang, Pasquale, Blackburn, & Lephart, 2009) have

demonstrated with fwEMG analysis, decreased rotator cuff coactivation (subscapularis-

infraspinatus and supraspinatus-infraspinatus) and abnormal deltoid activation (increased middle

deltoid activation from 0-30˚) during humeral elevation in 10 subjects with subacromial

impingent when compared to 10 healthy controls and the authors hypothesized this was

contributing to their symptoms.

Isokinetic testing has also demonstrated lower protraction/retraction ratios in 30 overhead

athletes with chronic shoulder impingement when compared to controls (Cools, Witvrouw,

Mahieu, & Danneels, 2005). Decreased isokinetic force output has also been demonstrated in the

protractor muscles of overhead athletes with impingement (-13.7% at 60degrees/s; -15.5% at

180degrees/s) (Cools, Witvrouw, Mahieu, & Danneels, 2005).

2.5 REHABILITATION CONSIDERATIONS

Current treatment of impingement generally starts with conservative methods, including

arm rest, physical therapy, nonsteroidal anti-inflammatory drugs (NSAIDs), and subacromial

corticosteroids injections (de Witte, et al., 2011). While it is beyond the scope of this paper,

interventions should be based on a thorough and accurate clinical examination including

observations, posture evaluation, manual muscle testing, individual joint evaluation, functional

testing, and special testing of the shoulder complex. Based on this clinical examination and

stage of healing, treatments and interventions are prescribed and, while each form of treatment

is important, this section of the paper will primarily focus on the role of prescribing specific

therapeutic exercise in rehabilitation. Also of importance but beyond the scope of this paper, is

applying the appropriate exercise progression based on pathology, clinical examination, and

healing stage.

Current treatments in rehabilitation aim to addresses the type of shoulder pathology

involved and present dysfunctions including compensatory patterns of movement, poor motor

control, shoulder mobility/stability, thoracic mobility, and finally decrease pain in order to

return the individual to their prior level of function. As our knowledge of specific muscular

activity and biomechanics have increased, a gradual progression towards more scientifically

based rehabilitation exercises, which facilitate recovery while placing minimal strain on healing

tissues, have been reported in the literature (Reinold, Escamilla, & Wilk, 2009). When treating

overhead athletes with impingement, the stage of the soft tissue lesion will have an important

impact on the prognosis for conservative treatment and overall recovery. Understanding the

previously discussed biomechanical factors of normal shoulder function, pathological shoulder

function, and the performed exercise is necessary to safely and effectively design and prescribe

appropriate therapeutic exercise programs.

2.5.1 Rehabilitation protocols in impingement

Typical treatments of impingement in the clinical setting of physical therapy include

specific supervised exercise, manual therapy, posture education, flexibility exercises, taping, and

modality treatments and are administered based on the phase of treatment (acute, intermediate,

advanced strengthening, or return to sport). For the purpose of this paper, the focus will be on

specific supervised exercise which refers to addressing individual muscles with therapeutic

exercise geared to address the strength or endurance deficits in that particular muscle. The

muscles which are the foci in rehabilitation include the rotator cuff (RTC) (supraspinatus,

infraspinatus, teres minor, and subscapularus), scapular stabilizers (rhomboid major and minor,

upper trapezius, lower trapezius, middle trapezius, serratus anterior), deltoid, and accessory

muscles (latisimmus dorsi, biceps brachii, coracobrachialis, pectoralis major, pectoralis minor).

Recent research has demonstrated strengthening exercises focusing on certain muscles

(serratus anterior, trapezius, infraspinatus, supraspinatus, and teres minor) may be more

beneficial for athletes with impingement and exercise prescription should be based on the EMG

activity profile of the exercise (Reinold, Escamilla, & Wilk, 2009). In order to prescribe the

appropriate exercise based on scientific rationale, the muscle EMG activity profile of the

exercise must be known and various authors have found different results with the same exercise

(See APPENDIX). Another important component is focusing on muscles which are known to be

dysfunctional in the shoulder impingement population, specifically the lower and middle

trapezius, serratus anterior, supraspinatus, and infraspinatus.

Numerous researchers have demonstrated the 3 parts of trapezius generally acting as a

scapular upward rotator and elevator (upper trapezius), a scapular retractor (middle trapezius),

and a downward rotator and depressor (lower trapezius)(Reinold, Escamilla, & Wilk, 2009). The

lower trapezius has also contributed to scapular posterior tilting and external rotation during

elevation, which is hypothesized to decrease impingement risk (Ludewig & Cook, 2000) and

make the lower trapezius vitally important in rehabilitation. Upper trapezius EMG activity has

demonstrated a progressive increase from 0-60˚, remain constant from 60-120˚, and increased

from 120-180˚ during elevation (Bagg & Forrest, 1986). In contrast, the lower trapezius EMG

activity tends to be low during elevation, flexion, and abduction below 90˚ and then

progressively increases from 90˚-180˚ (Bagg & Forrest, 1986; Ekstrom, Donatelli, & Soderberg,

2003; Hardwick, Beebe, McDonnell, & Lang, 2006; Moseley, Jobe, Pink, Perry, & Tibone,

1992; Smith, et al., 2006).

Several exercises have been recommended in order to maximally activate the lower

trapezius and the following exercises have demonstrated a high moderate to maximal (65-100%)

contraction including: 1) prone horizontal abduction at 135˚ with ER (97±16%MVIC; Ekstrom,

Donatelli, & Soderberg, 2003); 2) standing ER at 90˚ abduction (88±51%MVIC; Myers,

Pasquale, Laudner, Sell, Bradley, & Lephart, 2005); 3) prone ER at 90˚ abduction

(79±21%MVIC; Ekstrom, Donatelli, & Soderberg, 2003); 4) prone horizontal abduction at 90˚

abduction with ER (74±21%MVIC; Ekstrom, Donatelli, & Soderberg, 2003)(63±41%MVIC;

Moseley, Jobe, Pink, Perry, & Tibone, 1992); 5) abduction above 120˚ with ER (68±53%MVIC;

Moseley, Jobe, Pink, Perry, & Tibone, 1992); and 6) prone rowing (67±50%MVIC; Moseley,

Jobe, Pink, Perry, & Tibone, 1992).

Significantly greater EMG activity has been reported in prone ER at 90˚ when compared

to the empty can exercise (Ballantyne, et al., 1993) and authors have reported significant EMG

amplitude during prone ER at 90˚, prone full can, and prone horizontal abduction at 90˚ with ER

(Ekstrom, Donatelli, & Soderberg, 2003). Based on these results, it appears that obtaining

maximal EMG activity of the lower trapezius in prone exercises, requires performing exercises

prone approximately 120-130˚ of abduction may be most beneficial and will fluctuate depending

on body type. It is also important to note that these exercises have been performed in prone

instead of standing. Typically symptoms of SIS are increased during standing abduction greater

than 90˚, therefore this exercise is performed in the scapular plane with shoulder external

rotation in order to clear the subacromial structures from impinging on the acromion and should

not be performed during the acute phase of healing in SIS.

It is often clinically beneficial to enhance the ratio of lower trapezius to upper trapezius

in rehabilitation. Poor posture and muscle imbalance is often seen in shoulder impingement

along with alterations in the force couple between the upper trapezius and serratus anterior.

McCabe and colleagues (McCabe, Orishimo, McHugh, & Nicholas, 2007) demonstrated that

“the press up” (56%MVIC) and “scapular retraction” (40%MVIC) exercises exhibited

significantly greater lower trapezius sEMG activity than the “bilateral shoulder external

rotation” and “scapular depression” exercise. The authors also demonstrated that the “bilateral

shoulder external rotation” and “the press up” demonstrated the highest UT:LT ratios at 2.35 and

2.07 (McCabe, Orishimo, McHugh, & Nicholas, 2007). Even with the authors proposed

interpretation to apply to patient population; it is difficult to apply the results to a patient since

the experiment was performed on a healthy population.

The middle trapezius has demonstrated high EMG activity during elevation at 90˚ and

>120˚ (Bagg & Forrest, 1986; Decker, Hintermeister, Faber, & Hawkins, 1999; Ekstrom,

Donatelli, & Soderberg, 2003), while other authors have shown low EMG activity in the same

exercise (Moseley, Jobe, Pink, Perry, & Tibone, 1992).

However, several exercises have been recommended in order to maximally activate the

middle trapezius and the following exercises have demonstrated a high moderate to maximal

(65-100%) contraction including: 1) prone horizontal abduction at 90˚ abduction with IR

(108±63%MVIC; Moseley, Jobe, Pink, Perry, & Tibone, 1992); 2) prone horizontal abduction at

135˚ abduction with ER (101±32%MVIC; Ekstrom, Donatelli, & Soderberg, 2003); 3) prone

horizontal abduction at 90˚ abduction with ER (87±20%MVIC; Ekstrom, Donatelli, &

Soderberg, 2003)(96±73%MVIC; Moseley, Jobe, Pink, Perry, & Tibone, 1992); 4) prone rowing

(79±23%MVIC; Ekstrom, Donatelli, & Soderberg, 2003); and 5) prone extension at 90˚ flexion

(77±49%MVIC; Moseley, Jobe, Pink, Perry, & Tibone, 1992). In the” prone horizontal

abduction at 90˚ abduction with ER” exercise, the authors demonstrated some agreement in

amplitude of EMG activity. One author demonstrated 87±20%MVIC (Ekstrom, Donatelli, &

Soderberg, 2003) while a second demonstrated 96±73%MVIC (Moseley, Jobe, Pink, Perry, &

Tibone, 1992), while these amplitudes are not exact they are both considered maximal EMG

activity.

The supraspinatus is also a very important muscle to focus on in rehabilitation of SIS due

to the numerous force couples it is involved in and the potential for injury during SIS. Initially

Jobe (Jobe & Moynes, 1982) recommended scapular plane elevation with glenohumeral IR

(empty can) exercises to strengthen the supraspinatus muscle, but other authors (Poppen &

Walker, 1978; Reinold, et al., 2004) have suggested scapular plane elevation with glenohumeral

ER (full can) exercises. Recently, evidence based therapeutic exercise prescriptions have

avoided the use of the empty can exercise due to the increased deltoid activity potentially

increasing the amount of superior humeral head migration and the inability of a weak RTC to

counteract the force in the impingement population (Reinold, Escamilla, & Wilk, 2009).

Several exercises have been recommended in order to maximally activate the

supraspinatus and the following exercises have demonstrated a high moderate to maximal (65-

100%) contraction including: 1) push-up plus (99±36%MVIC; Decker, Tokish, Ellis, Torry, &

Hawkins, 2003), 2) prone horizontal abduction at 100˚ abduction with ER (82±37%MVIC;

Reinold et al., 2004); 3) prone ER at 90˚ abduction (68±33%MVIC; Reinold et al., 2004); 4)

military press (80±48%MVIC; Townsend, Jobe, Pink, & Perry, 1991); 5) scaption above 120˚

with IR (74±33%MVIC; Townsend, Jobe, Pink, & Perry, 1991); and 6) flexion above 120˚ with

ER (67±14%MVIC; Townsend, Jobe, Pink, & Perry, 1991)(42±21%MVIC; Myers, Pasquale,

Laudner, Sell, Bradley, & Lephart, 2005). Interestingly, some of the same exercises showed

different results in the EMG amplitude in different studies. For example, “flexion above 120˚

with ER” demonstrated 67±14%MVIC (Townsend, Jobe, Pink, & Perry, 1991) in one study and

42±21%MVIC (Myers, Pasquale, Laudner, Sell, Bradley, & Lephart, 2005) in another study. As

you can see this is a large disparity but potential mechanisms for the difference may be due to the

fact that one study used dumbbell’s and the other used resistance tubing. Also the participants

weren’t given a weight based on a ten repetition maximum.

3-D biomechanical model data implies that the infraspinatus is a more effective shoulder

ER at lower angles of abduction (Reinold, Escamilla, & Wilk, 2009) and numerous studies have

tested this model with conflicting results in exercise selection (Decker, Tokish, Ellis, Torry, &

Hawkins, 2003; Myers, Pasquale, Laudner, Sell, Bradley, & Lephart, 2005; Townsend, Jobe,

Pink, & Perry, 1991; Reinold, et al., 2004). In general infraspinatus and teres minor activity

progressively decrease as the shoulder moves into the abducted position while the supraspinatus

and deltoid increase activity.

Several exercises have been recommended in order to maximally activate the

infraspinatus, the following exercises have demonstrated a high moderate to maximal (65-

100%) contraction including: 1) push-up plus (104±54%MVIC; Decker, Tokish, Ellis, Torry, &

Hawkins, 2003); 2) SL ER at 0˚ abduction (62±13%MVIC; Reinold et al., 2004)

(85±26%MVIC, Townsend, Jobe, Pink, & Perry, 1991); 3) prone horizontal abduction at 90˚

abduction with ER (88±25%MVIC; Townsend, Jobe, Pink, & Perry, 1991); 4) prone horizontal

abduction at 90˚ abduction with IR (74±32%MVIC; Townsend, Jobe, Pink, & Perry, 1991); 5)

abduction above 120˚ with ER (74±23%MVIC; Townsend, Jobe, Pink, & Perry, 1991); and 6)

flexion above 120˚ with ER (66±16%MVIC; Townsend, Jobe, Pink, & Perry, 1991)

(47±34%MVIC; Myers, Pasquale, Laudner, Sell, Bradley, & Lephart, 2005).

Reinold and colleagues (Reinold, et al., 2004) also examined several exercises,

commonly used in rehabilitation, used to strengthen the posterior RTC and specifically the

infraspinatus and teres minor. The authors determined that 3 exercise’s demonstrated the best

combined EMG activity and in order include: 1) side lying ER (infraspinatus, 62%MVIC; teres

minor, 67%MVIC); 2) standing ER in scapular plane at 45˚ abduction (infraspinatus,

53%MVIC; teres minor, 55%MVIC); and 3) prone ER in the 90˚ abducted position

(infraspinatus, 50%MVIC; teres minor, 48%MVIC). The 90˚ abducted position is commonly

used in overhead athletes to simulate the throwing position in overhead athletes. The side lying

ER exercise is also clinically significant since it exerts less capsular strain, specifically on the

anterior band of the glenohumeral ligament (Reinold, et al., 2004), than the more functionally

advantageous standing ER at 90˚. It has also been demonstrated that the application of a towel

roll while performing ER at 0˚ increases EMG activity by approximately 20% when compared to

no towel roll (Reinold, et al., 2004).

The serratus anterior contributes to scapular posterior tilting, upward rotation, and

external rotation of the scapula (Ludewig & Cook, 2000; McClure, Michener, & Karduna, 2006)

and has demonstrated decreased EMG activity in the impingement population (Cools et al.,

2007; Cools, Witvrouw, Declercq, Danneels, & Cambier, 2003; Wadsworth & Bullock-Saxton,

1997). Serratus anterior activity tends to increase as arm elevation increases; however, increased

elevation may also increase impingement symptoms and risk (Reinold, Escamilla, & Wilk,

2009). Interestingly, performing 90˚ shoulder abduction with IR or ER has generated high

serratus anterior activity, while initially Jobe (Jobe & Moynes, 1982) recommended IR or ER for

rotator cuff strengthening. Serratus anterior activity also increases as the gravitational challenge

increased when comparing the wall push up plus, push-up plus on knees, and push up plus with

feet elevated (Reinold, Escamilla, & Wilk, 2009).

Prior authors have recommended the push-up plus, dynamic hug, and punch exercise to

specifically recruit the serratus anterior (Decker, Hintermeister, Faber, & Hawkins, 1999) while

other authors’ (Ekstrom, Donatelli, & Soderberg, 2003) data indicated that performing

movements which create scapular upward rotation/protraction (punch at 120˚ abduction) and

diagonal exercises incorporating flexion, horizontal abduction, and ER.

Hardwick and colleges (Hardwick, Beebe, McDonnell, & Lang, 2006) contrary to

previous authors (Ekstrom, Donatelli, & Soderberg, 2003) demonstrated no statistical difference

in serratus anterior EMG activity during the wall slide, push-up plus (only at 90˚), and scapular

plane shoulder elevation in 20 healthy individuals measured at 90˚, 120˚, and 140˚. The study

also demonstrated that the wall slide and scapular plane shoulder elevation EMG activity was

highest at 140˚ (approximately 76%MVIC and 82%MVIC). However, these results should be

interpreted with caution since the methodological issues of limited healthy sample and only the

plus phase of the push up plus exercise was examined in the study.

The serratus anterior is important for the acceleration phase of overhead throwing and

several exercises have been recommended to maximally activate this muscle. The following

exercises have demonstrated a high moderate to maximal (65-100%) contraction including: 1)

D1 diagonal pattern flexion, horizontal adduction, and ER (100±24%MVIC; Ekstrom, Donatelli,

& Soderberg, 2003); 2) scaption above 120˚ with ER (96±24%MVIC; Ekstrom, Donatelli, &

Soderberg, 2003)(91±52%MVIC Middle Serratus, 84±20%MVIC Lower Serratus; Moseley,

Jobe, Pink, Perry, & Tibone, 1992); 3) supine upward punch (62±19%MVIC; Ekstrom,

Donatelli, & Soderberg, 2003); 4) flexion above 120˚ with ER(96±45%MVIC Middle Serratus,

72±46%MVIC Lower Serratus; Moseley, Jobe, Pink, Perry, & Tibone, 1992) (67±37%MVIC;

Myers, Pasquale, Laudner, Sell, Bradley, & Lephart, 2005); 5) abduction above 120˚ with ER

(96±53%MVIC Middle Serratus, 74±65%MVIC Lower Serratus; Moseley, Jobe, Pink, Perry, &

Tibone, 1992); 7) military press (82±36%MVIC Middle Serratus, 60±42%MVIC Lower

Serratus; Moseley, Jobe, Pink, Perry, & Tibone, 1992); 7) push-up plus (80±38%MVIC Middle

Serratus, 73±3%MVIC Lower Serratus; Moseley, Jobe, Pink, Perry, & Tibone, 1992); 8) push-

up with hands separated (57±36%MVIC Middle Serratus, 69±31%MVIC Lower Serratus;

Moseley, Jobe, Pink, Perry, & Tibone, 1992); 9) standing ER at 90˚ abduction (66±39%MVIC;

Myers, Pasquale, Laudner, Sell, Bradley, & Lephart, 2005); and 10) standing forward scapular

punch (67±45%MVIC; Myers, Pasquale, Laudner, Sell, Bradley, & Lephart, 2005).

Even though the research has demonstrated exercises which may be more beneficial than

others, the lack of statistical analysis, lack of data, and absence of the significant muscle activity

(including the deltoid) were methodological limitations of these studies. Also, while performing

exercises with a high EMG activity are the most effective to maximally exercise specific

muscles, the stage of rehabilitation may contraindicate the specific exercise recommended. For

example, it is generally accepted that performing standing exercises below 90˚ elevation is

necessary to avoid exacerbations of impingement symptoms. In conclusion, the previously

described therapeutic exercises have demonstrated clinical benefit and high EMG activity in the

prior discussed muscles (Table 5).

2.5.2 Rehabilitation of scapula dyskinesis

Scapular rehabilitation should be based on an accurate and thorough clinical evaluation

performed by an individual licensed to evaluate and treat dysfunction to permit appropriate goal

setting and rehabilitation for the patient. A comprehensive initial patient interview is necessary

to ascertain the individual’s functional requirements and problematic activities followed by the

physical examination. The health care professional should address all possible deficiencies

found on different levels of the kinetic chain and appropriate treatment goals should be set

leading to proper rehabilitation strategies. Therefore, although considered to be key points in

functional shoulder and neck rehabilitation, more proximal links in the kinetic chain, such as

thoracic spine mobility and strength, core stability and lower limb function, will not be addressed

in this manuscript.

Treatment of scapular dyskinesis is only successful if the anatomical base is optimal and

the individual does not exhibit problems which require surgery such as nerve injury, scapular

muscle detachment, severe bony derangement (acromioclavicular separation, fractured clavicle)

or soft tissue derangement (labral injury, rotator cuff disease, glenohumeral instability) (Kibler &

Sciascia, 2010; Wright, Wassinger, Frank, Michener, & Hegedus, 2012). The large majorities of

cases of dyskinesis, however, are caused by muscle weakness, inhibition or inflexibility, and can

be managed with rehabilitation.

Optimal rehabilitation of scapular dyskinesis requires addressing all of the causative

factors that can create the dyskinesis and then restoring the balance of muscle forces that allow

scapular position and motion. The emphasis of scapular dyskinesis rehabilitation should start

proximally and end distally with an initial goal of achieving the position of optimal scapular

function (posterior tilt, external rotation and upward elevation). The serratus anterior is an

important external rotator of the scapula, and the lower trapezius is a stabilizer of the acquired

scapular position. Scapular stabilization protocols should focus on re-educating these muscles to

act as dynamic scapula stabilizers, first by the implementation of short lever, kinetic chain

assisted exercises then progress to long lever movements. Maximal rotator cuff strength is

achieved off a stabilized, retracted scapula and rotator cuff emphasis should be after scapular

control is achieved (Kibler & Sciascia, 2010). An increase in impingement pain when doing

open chain rotator cuff exercises indicates an incorrect protocol emphasis and stage of

rehabilitation. A logical progression of exercises (isometric to dynamic) focused on

strengthening the lower trapezius and serratus anterior while minimizing upper trapezius

activation has been described in the literature (Kibler & Sciascia, 2010; Kibler, Ludewig,

McClure, Michener, Bak, & Sciascia, 2013), and on an algorithm guideline (Figure 3) has been

proposed that is based on restoration of soft tissue inflexibilities and maximizing muscle

performance (Cools, Struyf, De Mey, Maenhout, Castelein, & Cagnie, 2013).

Several principles guide the progression through the algorithm with the first requirement

being acquisition of flexibility in muscles and joints because tight muscles and joint capsules can

inhibit strength activation. Also, later protocols in rehabilitation should train functional

movements in sport or activity specific patterns since research has demonstrated maximal

scapular muscle activation when muscles are activated in functional patterns (vs isolated)(i.e.

when the muscles are activated in specific diagonal patterns using kinetic chain sequencing)

(Kibler & Sciascia, 2010). Using these principles, many rehabilitation interventions can be

considered, but a reasonable program could start with standing low-load/low-activation (activate

the scapular retractors >20% MVIC) exercises with the arm below shoulder level and progress

to prone and side-lying exercises that increase the load, but still emphasize lower trapezius and

Figure 3: A scapular rehabilitation algorithm guideline (Adapted from Cools, Struyf, De Mey,

Maenhout, Castelein, & Cagnie, 2013).

serratus anterior activation over upper trapezius activation. Additional loads and activations can

be stimulated by integrating ipsilateral and contralateral kinetic chain activation and adding

distal resistance. Final optimization of activation can occur through weight training emphasizing

proper retraction and stabilization. Progression can be made by increasing holding time,

repetitions, resistance, and speed parameters of exercise relevant to the patient’s functional

needs.

The lower trapezius is frequently inhibited in activation, and specific effort may be

required to ‘jump start’ it. Tightness, spasm and hyperactivity in the upper trapezius, pectoralis

minor and latissimus dorsi are frequently associated with lower trapezius inhibition, and specific

therapy should address these muscles.

Multiple studies have identified methods to activate scapular muscles that control

scapular motion and have identified effective body and scapular positions that allow optimal

activation in order to improve scapular muscle performance and decrease clinical symptoms.

Only two randomized clinical trials have examined the effects of a scapular focused program by

comparing it to a general shoulder rehabilitation, and the findings indicate the use of scapular

exercises results in higher patient-rated outcomes (Başkurt, Başkurt, Gelecek, & Özkan, 2011;

Struyf, Nijs, Mollekens, Jeurissen, Truijen, Mottram, & Meeusen, 2013).

Multiple clinical trials have incorporated scapular exercises within their rehabilitation

programs and have found positive patient-rated outcomes in patients with impingement

syndrome (Kromer, Tautenhahn, de Bie, Staal, & Bastiaenen, 2009). It appears that it is not only

the scapular exercises but also the inclusion of the scapular exercises as part of a rehabilitation

program that may include the use of the kinetic chain is what achieves positive outcomes. When

the scapular exercises are prescribed, multiple components must be emphasized, including

activation sequencing, force couple activation, concentric/eccentric emphasis, strength,

endurance and avoidance of unwanted patterns (Cools, Struyf, De Mey, Maenhout, Castelein, &

Cagnie, 2013).

2.5.3 Effects of rehabilitation

Conservative therapy is successful in 42% (Bigliani type III) to 91% (Bigliani type I) (de

Witte, et al., 2011) and most shoulder injuries in the overhead thrower can be successfully

treated non-operatively (Wilk, Obma, Simpson, Cain, Dugas, & Andrews, 2009). Evidence

supports the use of thoracic mobilizations (Theisen, et al., 2010), glenohumeral mobilizations

(Tyler, Nicholas, Lee, Mullaney, & Mchugh, 2012; Sauers, 2005), supervised shoulder and

scapular muscle strengthening (Fleming, Seitz, & Edaugh, 2010; Osteras, Torstensen, &

Osteras, 2010; McClure, Bialker, Neff, Williams, & Karduna, 2004; Sauers, 2005; Bang &

Deyle, 2000; Senbursa, Baltaci, & Atay, 2007), supervised shoulder and scapular muscle

strengthening with manual therapy (Bang & Deyle, 2000; Senbursa, Baltaci, & Atay, 2007),

taping (Lin, Hung, &

Yang, 2011; Williams, Whatman, Hume, & Sheerin, 2012; Selkowitz, Chaney, Stuckey, & Vlad,

2007; Smith, Sparkes, Busse, & Enright, 2009), and laser therapy (Sauers, 2005) in decreasing

pain, increasing mobility, improving function, and improving altering muscle activity of shoulder

muscles.

In systematic reviews of randomized controlled trials, there is a lack of high quality

intervention studies, but some studies suggest that therapeutic exercise is as effective as surgery

in SIS (Nyberg, Jonsson, & Sundelin, 2010; Trampas & Kitsios, 2006), the combination of

manual therapy and exercise is better than exercise alone in SIS (Michener, Walsworth, &

Burnet, 2004), and high dosage exercise is better than low dosage exercise in SIS (Nyberg,

Jonsson, & Sundelin, 2010) in reducing pain and improving function. In evidence-based clinical

practice guidelines, therapeutic exercise is effective in treatment of SIS (Trampas & Kitsios,

2006; Kelly, Wrightson, & Meads, 2010) and is recommended to be combined with joint

mobilization of the shoulder complex (Tyler, Nicholas, Lee, Mullaney, & Mchugh, 2012;

Sauers, 2005). Joint mobilization techniques have demonstrated increased improvements in

symptoms when applied by experienced physical therapists rather than applied by novice

clinicians (Tyler, Nicholas, Lee, Mullaney, & Mchugh, 2012). A course of therapeutic exercise

in the SIS population has also been shown to be more beneficial than no treatment or a placebo

treatment, and should be attempted to reduce symptoms and restore function before surgical

intervention is considered (Michener, Walsworth, & Burnet, 2004).

In a study by McClure and colleagues (McClure, Bialker, Neff, Williams, & Karduna,

2004), the authors demonstrated, after a 6 week therapeutic exercise program combined with

education, significant improvements in pain, shoulder function, increased passive range of

motion, increased ER and IR force, and no changes in scapular kinematics in a SIS population.

However, these results should be interpreted with caution since the rate of attrition was 33%,

there was no control group, and numerous clinicians performed the interventions.

In a randomized clinical trial by Conroy & Hayes (Conroy & Hayes, 1998), 14 patients

with SIS underwent either a supervised exercise program or a supervised exercise program with

joint mobilization for 9 sessions over 3 weeks. At 3 weeks, the supervised exercise program

with joint mobilization had less pain compared to the supervised exercise program group. In a

larger randomized clinical trial by Bang & Deyle (Bang & Deyle, 2000), patients’ with SIS

underwent either an exercise program or an exercise program with manual therapy for 6 sessions

over 3-4 weeks. At the end of treatment and at 1 month follow up, the exercise program with

manual therapy group had superior gains in strength, function, and pain compared to the

exercise program group.

Recently, numerous studies have observed the EMG activity in the shoulder complex

musculature during numerous rehabilitation exercises. In exploring evidence-based exercises

while treating SIS the population, the following has been shown to be effective to improve

outcome measures for this population: 1) serratus anterior strengthening, 2) scapular control with

external rotation exercises, 3) external rotation exercises with tubing, 4) resisted flexion

exercises, 5) resisted extension exercises, 6) resisted abduction exercise, 7) resisted internal

rotation exercise (Dewhurst, 2010).

Table 7: Therapeutic exercises for the shoulder musculature, which is involved in rehabilitation, that has demonstrated a moderate to maximal EMG profile for that particular

muscle along with its clinical significance (DB=dumbbell, T=Tubing)

Muscle Exercise Clinical Significance

lower

trapeziu

1. Prone horizontal abduction at 135˚ with ER (DB)

2. Standing ER at 90˚ (T)

3. Prone ER at 90˚ abd (DB)

4. Prone horizontal abduction at 90˚ with ER (DB)

5. Abd > 120˚ with ER (DB)

6. Prone rowing (DB)

1. In line with lower trapezius fibers, High EMG activity of trapezius, effective/good supraspinatus/serratus anterior

2. High EMG activity lower trap, rhomboids, serratus anterior; moderate-maximal EMG activity of RTC

3. Below 90˚ abduction; High EMG of lower trapezius

4. Below 90˚ abduction, good UT:LT ratio, moderate to maximal EMG of upper, middle and lower trapezius

5. Used later in rehabilitation since >90˚ abduction can  symptoms, high serratus anterior EMG, moderate upper and lower

trapezius EMG

6. Below 90˚ abduction, High EMG of upper, middle, and lower trapezius

middle

trapeziu

1. Prone horizontal abduction at 90˚ with IR (DB)

2. Prone horizontal abduction at 135˚ with ER (DB)

3. Prone horizontal abduction at 90˚ with ER (DB)

4. Prone rowing (DB)

5. Prone extension at 90˚ flexion (DB)

1. IR  tension on subacromial structures,  deltoid activity not for patient with SIS, high EMG for all parts of trapezius

2. High EMG activity of all parts of trapezius, effective and good for supraspinatus and serratus anterior also

3. Below 90˚ abduction, good UT:LT ratio, moderate to maximal EMG of upper, middle and lower trapezius

4. Below 90˚ abduction, High EMG of upper, middle, and lower trapezius

5. Below 90˚ abduction, High middle trapezius activity

serratus

1. D1 diagonal pattern flexion, horizontal adduction,

and ER (T)

2. Scaption above 120˚ with ER (DB)

3. Supine upward punch (DB)

4. Flexion above 120˚ with ER (DB)

5. Abduction above 120˚ with ER (DB)

6. Military press (DB)

7. Push-up Plus

8. Push-up with hands separated

9. Standing ER at 90˚ abduction (T)

10. Standing forward scapular punch (T)

1. Effective to begin functional movements patterns later in rehabilitation, high EMG activity

2. Above 90˚ to be performed after resolution of symptoms

3. Effective and below 90˚

4. Above 90˚ to be performed after resolution of symptoms

5. Used later in rehabilitation since >90˚ abduction can  symptoms, high serratus anterior EMG, moderate upper and lower

trapezius EMG

6. Perform in advanced strengthening phase since can cause impingement

7. Closed chain exercise below 90˚, high serratus anterior, supraspinatus, and infraspinatus activity

8. Closed chain exercise

9. High teres minor, lower trapezius and rhomboid EMG activity

10. Below 90˚ abduction, high subscapularis and teres minor EMG activity

suprasp

inatus

1. Push-up plus

2. Prone horizontal abduction at 100˚ with ER (DB)

3. Prone ER at 90˚ abd (DB)

4. Military press (DB)

5. Scaption above 120˚ with IR (DB)

6. Flexion above 120˚ with ER (DB)

1. Closed chain exercise below 90˚, high serratus anterior, supraspinatus, and infraspinatus activity

2. High supraspinatus, middle/posterior deltoid EMG activity

3. Below 90˚ abduction; High EMG of lower trapezius also

4. Perform in advanced strengthening phase since can cause impingement

5. IR  tension on subacromial structures,  anterior/middle deltoid activity not for patient with SIS moderate infraspinatus

EMG activity

6. High anterior/middle deltoid activity not for patient with SIS, moderate infraspinatus and subscapularis EMG activity

Table 7: Therapeutic exercises for the shoulder musculature, which is involved in rehabilitation, that has demonstrated a moderate to maximal EMG profile for that particular

muscle along with its clinical significance (DB=dumbbell, T=Tubing)(Continued)

Muscle Exercise Clinical Significance

Infraspi

natus

1. Push-up plus

2. SL ER at 0˚ abduction (DB)

3. Prone horizontal abduction at 90˚ with ER (DB)

4. Prone horizontal abduction at 90˚ with IR (DB)

5. Abduction > 120˚ with ER (DB)

6. Flexion above 120˚ with ER (DB)

1. Closed chain exercise below 90˚, high serratus anterior, supraspinatus, and infraspinatus activity

2. Stable shoulder position; Most effective exercise to recruit infraspinatus

3. Below 90˚ abduction, good UT:LT ratio, moderate to maximal EMG of upper, middle and lower trapezius

4. IR increases tension on subacromial structures, increased deltoid activity not for patient with SIS, high EMG for all parts

of trapezius

5. Used later in rehabilitation since >90˚ abduction can increase symptoms, high serratus anterior EMG, moderate upper

and lower trapezius EMG

6. High anterior/middle deltoid activity not for patient with SIS, moderate infraspinatus and subscapularis EMG activity

Infraspi

natus &

Teres

minor

1. SL ER at 0˚ abduction (DB)

2. Standing ER in scapular plane at 45˚ abduction

(DB)

3. Prone ER in 90˚ abduction (DB)

1. Stable shoulder position; Most effective exercise to recruit infraspinatus

2. High EMG of teres and infraspinatus

3. Below 90˚ abduction; High EMG of lower trapezius

However, no studies have explored whether or not specific rehabilitation exercises

targeting muscles, based on EMG profile, could correct prior EMG deficits and speed recovery

in patients with shoulder impingement. In conclusion, there is a need for further well-defined

clinical trials on specific exercise interventions for the treatment of SIS. This literature reveals

the need for improved sample sizes, improved diagnostic criteria and similar diagnostic criteria

applied between studies, longer follow ups, studies measuring function and pain, and

(specifically in overhead athletes) sooner return to play.

2.6 SUMMARY

Overhead athletes with SIS or shoulder impingement will exhibit muscle imbalances and

tightness in the GH and scapular musculature. These dysfunctions can lead to altered shoulder

complex kinematics, altered EMG activity, and functional limitations, which will cause

impingement. The exact mechanism of impingement is debated in the literature as well its

relation to scapular kinematic variation. Therapeutic exercise has shown to be beneficial in

alleviating dysfunctions and pain in SIS, and supervised exercise with manual techniques by an

experienced clinician is an effective treatment. It is unknown whether prescribing specific

therapeutic exercise based on EMG profile will speed the recovery time, increase force

production, resolve scapular dyskinesis, or change SAS height in SIS. Few research articles

have examined these variables and its association with prescribing specific therapeutic exercise

and there is a general need for further well-defined clinical trials on specific exercise

interventions for the treatment of SIS.

CHAPTER 3: THE EFFECT OF VARIOUS POSTURES ON THE SURFACE

ELECTROMYOGRAPHIC ANALYSIS OF THE LOWER TRAPEZIUS DURING

SPECIFIC THERAPEUTIC EXERCISE

3.1 INTRODUCTION

Individuals diagnosed with shoulder impingement exhibit muscle imbalances in the

shoulder complex and specifically in the force couple (lower trapezius, upper trapezius, and

serratus anterior), which controls scapular movements. The deltoid plays an important role in the

muscle force couple since it is the prime mover of the glenohumeral joint. Dysfunctions in these

muscles lead to altered shoulder complex kinematics and functional limitations, which will cause

an increase in impingement symptoms. Therapeutic exercises are beneficial in alleviating

dysfunctions and pain in individuals diagnosed with shoulder impingement. However, no studies

demonstrate the effect various postures will have on electromyographic (EMG) activity in

healthy adults or in adults with impingement during specific therapeutic exercise. The purpose

of the study was to identify the therapeutic exercise and posture which elicits the highest EMG

activity in the lower trapezius shoulder muscle tested. This study also tested the exercises and

postures in the healthy population and the shoulder impingement population since very few

studies have correlated specific therapeutic exercises in the shoulder impingement population.

Individuals with shoulder impingement exhibit muscle imbalances in the shoulder

complex and specifically in the lower trapezius, upper trapezius, and serratus anterior, all of

which control scapular movements, with the deltoid acting as the prime mover of the shoulder.

Dysfunctions in these muscles lead to altered kinematics and functional limitations,

which cause an increase in impingement symptoms. Therapeutic exercise has shown to be

beneficial in alleviating dysfunctions and pain in impingement and the following exercises have

been shown to be effective treatment to improve outcome measures for this diagnosis: 1)

serratus

anterior strengthening, 2) scapular control with external rotation exercises, 3) external rotation

exercises, 4) prone extension, 5) press up exercises, 6) bilateral shoulder external rotation

exercise, and 7) prone horizontal abduction exercises at 135˚ and 90˚ of abduction (Dewhurst,

2010; Trampas & Kitsios, 2006; Kelly, Wrightson, & Meads, 2010; Fleming, Seitz, & Edaugh,

2010; Osteras, Torstensen, & Osteras, 2010; McClure, Bialker, Neff, Williams, & Karduna,

2004; Sauers, 2005;; Senbursa, Baltaci, & Atay, 2007; Bang & Deyle, 2000; Senbursa, Baltaci,

& Atay, 2007). The therapeutic exercises in this study were derived from specific therapeutic

exercises shown to improve outcomes in the impingement population and of particular

importance are the amount of EMG activity in the lower trapezius since this muscle is directly

responsible for stabilizing the scapula.

Evidence based treatment of impingement requires a high dosage of therapeutic exercises

over a low dosage (Nyberg, Jonsson, & Sundelin, 2010) and applying the exercise EMG profile

to exercise prescription facilitates a speedy recovery. However, no studies have correlated the

effect various postures will have on the EMG activity of the lower trapezius in healthy adults or

in adults with impingement. The purpose of this study was to identify the therapeutic exercise

and posture which elicits the highest EMG activity in the lower trapezius muscle. The postures

included in the study include a normal posture with towel roll under the arm (if applicable), a

posture with the feet staggered/scapula retracted and a towel roll under the arm (if applicable),

and a normal posture/scapula retracted with a towel roll under the arm (if applicable) with a

physical therapist observing and cueing to maintain the scapula retraction. Recent research has

demonstrated that the application of a towel roll increases the EMG activity of the shoulder

muscles by 20% in certain exercises (Reinold, Wilk, Fleisig, Zheng, Barrentine, Chmielewski,

Cody, Jameson, & Andrews, 2004) thereby increasing the effectiveness of therapeutic exercise.

However, no studies have examined the effect of the towel roll in conjunction with

different postures or the effect of a physical therapist observing the movement and issuing

verbal and tactile cues.

This study addressed two current issues. First, it sought to demonstrate if it is more

beneficial to change posture in order to facilitate increased activity of the lower trapezius in

healthy individuals or individuals diagnosed with shoulder impingement. Second, it attempts to l

provide more clarity over which therapeutic exercise exhibits the highest percentage of EMG

activity in a healthy and pathologic population. Since physical therapists use therapeutic

exercise to target specific weak muscles, this study will better help determine which of the

selected exercises help maximally activate the target muscle, and allow for better exercise

selection and, although it is unknown in research, a hypothesized faster recovery time for an

individual with shoulder impingement.

3.2 METHODS

One investigator conducted the assessment for the inclusion and exclusion criteria

through the use of a verbal questionnaire. The inclusion criteria for all subjects are: 1) 18-50

years old, and 2) able to communicate in English. The exclusion criteria of the healthy adult

group (phase 1) include: 1) recent history (less than 1 year) of a musculoskeletal injury,

condition, or surgery involving the upper extremity or the cervical spine, and 2) a prior history

of a neuromuscular condition, pathology, or numbness or tingling in either upper extremity. The

inclusion criteria for the adult impingement group (phase 2) included: 1) recent diagnosis of

shoulder impingement by physician, 2) diagnosis confirmed by physical therapist (based on

having at least 4 of the following 7 criteria): 1) a Neer impingement sign, 2) a Hawkins sign, 3) a

positive empty or full can test, 4) pain with active shoulder elevation, 5) pain with palpation of

the rotator cuff tendons, 6) pain with isometric resisted abduction, and 7) pain in the C5 or C6

dermatome region (Table 8).

Table 8: Description of the inclusion criteria for the adult impingement group (phase 2)

Criteria Description

Neer impingement sign This is a reproduction of pain when the examiner passively flexes

the humerus, or shoulder, to the end range of motion and applies

overpressure

Hawkins sign This is reproduction of pain when the shoulder is passively

placed in 90˚ of forward flexion and internally rotated to the end

range of motion

positive empty or full can test pain with resisted forward flexion at 90˚ either with the thumb

pointing up (full can) or the thumb pointing down (empty can)

pain with active shoulder

elevation

pain during active shoulder elevation or shoulder abduction from

0-180 degrees

pain with palpation of the

rotator cuff tendons

pain with palpation of the shoulder muscles including the

supraspinatus, infraspinatus, teres minor, and subscapularus

pain with isometric resisted

abduction

pain with a manual muscle test where a downward force is placed

on the shoulder at the wrist while the shoulder is in 90 degrees of

abduction and the elbow is extended

pain in the C5 or C6

dermatome region

pain the C5 and C6 dermatome is located from the front and back

of the shoulder down to the wrist and hand, dermatomes correlate

to the nerve root level with the location of pain, so since the

rotator cuff is involved then then dermatome which will present

with pain includes the C5, C6 dermatomes since the rotator cuff

is innervated by that nerve root

The exclusion criteria of the adult impingement group included: 1) diagnosis and/or MRI

confirmation of a complete rotator cuff tear, 2) signs of acute inflammation including severe

resting pain or severe pain with resisted isometric abduction, 3) subjects who had previous spine

related symptoms or are judged to have spine related symptoms, 4) glenohumeral instability (as

determined by a positive apprehension test, anterior drawer, and sulcus sign; (Table 9), and 5) a

previous shoulder surgery. Subjects were also excluded if they exhibited any contraindications

to exercise (Table 10).

The study was explained to all subjects and they signed the informed consent agreement

approved by the Louisiana State University institutional review board. Subjects were screened

Table 9: Glenohumeral instability tests used in exclusion criteria of the adult impingement group

Test Procedure

apprehension

test

reproduction of pain when an anteriorly directed force is applied to the

proximal humerus in the position of 90˚ of abduction an 90˚ of external

rotation

anterior drawer subject supine and examiner stands facing the affected shoulder and holds it at

80-120° of abduction, 0-20° of forward flexion and 0-30° of external rotation.

The examiner holds the patients scapula spine forward with his index and

middle fingers; the thumb exerts counter pressure on the coracoid. The

examiner uses his right hand to grasp the patient's relaxed upper arm and

draws it anteriorly with a force. The relative movement between the fixed

scapula and the moveable humerus is appreciated and graded. An audible click

on forward movement of the humeral head due to labral pathology is a positive

sign

sulcus sign with the subject sitting, the elbow is grasped and an inferior traction is applied,

the area adjacent to the acromion is observed and if dimpling of the skin is

present then a positive sulcus sign is present

Table 10: Contraindications to exercise

1. a recent change in resting ECG suggesting significant ischemia

2. a recent myocardial infarction (within 7 days),

3. an acute cardiac event

4. unstable angina

5. uncontrolled cardiac dysrhythmias

6. symptomatic severe aortic stenosis

7. uncontrolled symptomatic heart failure

8. acute pulmonary embolus or pulmonary infarction

9. acute myocarditis or pericarditis

10. suspected or known dissecting aneurysm

11. acute systemic infection accompanied by fever, body aches,

or swollen lymph glands.

for latex allergies or current pregnancy. Pregnant individuals were excluded from the study and

individuals with latex allergy used the latex free version of the resistance band.

Phase 1 participants were recruited from university students, pre-physical therapy

students, and healthy individuals willing to volunteer. Phase 2 participants were recruited from

current physical therapy patients willing to volunteer who are diagnosed by a physician with

shoulder impingement and referred to physical therapy for treatment. Participants filled out an

informed consent, PAR-Q, HIPAA authorization agreement, and screened for the inclusion and

exclusion criteria through the use of a verbal questionnaire. Each phase participants was

randomized into one of three posture groups, blinded from the expected/hypothesized outcomes

of the study, and all exercises were counterbalanced.

Surface electrodes were applied and recorded EMG activity of the lower trapezius during

exercises and various postures in 30 healthy adults and 16 adults with impingement.

The

healthy subjects (phase 1) were randomized into one of three groups and performed ten

repetitions on each of seven exercises. The subjects with impingement (Phase 2) and were

randomized into one of three groups and perform ten repetitions on each of the same exercises.

The therapeutic exercises selected are common in rehabilitation of individuals diagnosed

with shoulder impingement and each subject performed ten repetitions of each exercise (Table

11) with the repetition speed regulated by a metronome set to sixty beats per minute (bpm). The

subject performed each concentric or eccentric phase of the exercise during 2 beats of the

metronome. The mass determination was based on a standardizing formula based on

anthropometrics and calculated the desired weight from height, arm length, and weight

measurements.

On the day of testing, the subjects were informed of their rights, procedures of

participating in this study, read and signed the informed consent, read and signed the HIPPA

authorization, discussed inclusion and exclusion criteria with examiner, received a brief

screening examination, and were oriented to the testing protocol. The protocol was sequenced as

follows: randomization, 10-repetition maximum determination, electrode placement, practice

and familiarization, MVIC testing, five minute rest, and exercise testing. In total, the study took

one hour of the individual’s time. Phase 1 participants (healthy adult subjects) were randomized

into 1 of three groups (Table 11). Group 1 consisted of specific therapeutic exercises performed

with

Table 11: Specific Therapeutic Exercises Descriptions and EMG activation

Group 1(control Group, not

altered posture):

1.Prone horizontal abduction at

90˚ abduction

2.Prone horizontal abduction at

130˚ abduction

3.Sidelying external rotation

4.Prone extension

5.Bilateral shoulder external

rotation

6.Prone ER at 90˚ abduction

7.Prone rowing

1. The subject is positioned prone with the shoulder resting at 90˚ forward flexion. From this position, the subject horizontally abducts the arm while

maintaining the shoulder at 90˚ abduction with the shoulder in external rotation (thumb up) until the arm reached the frontal plane. (without

conscious correction,)

2. The subject is positioned prone with the shoulder resting at 90˚ forward flexion. From this position, the subject horizontally abducts the arm while

maintaining the shoulder at 130˚ abduction with the shoulder in external rotation (thumb up) until the arm reached the frontal plane. (without

conscious correction,)

3. The subject is side lying with the arm at the side with a towel between the elbow and rib cage. The subject then externally rotates the shoulder to 50

degrees above the horizontal then returns back to resting position.

4. The subject is positioned prone with the arm resting at 90˚ forward flexion. The subject then extends the shoulder while keeping the hand in

supination (thumb pointing outward) until the arm reaches 5 degrees past the frontal plane then returns back to resting position.

5. The subject is standing with a taut elastic band in the subjects hand with the palms facing each other. The subject then bilaterally externally rotates

the shoulder while maintaining the shoulder and elbow position past 50 degrees from the sagittal plane and then returns to the resting position.

6. The subject is lying prone with the shoulder in 90˚ abduction and the elbow in 90˚ flexion the slight hand supination (thumb up). The subject then

lifts the arm off the mat in its entirety clearing the ulna and humerus from the mat then returns to the resting position. (without conscious

correction,)

7. The subject is lying prone with the arm resting at 90˚ forward flexion and hand in supination (thumb facing laterally). The subject then extends the

shoulder and flexes the elbow simultaneously until the hand is parallel to the body. The subject then returns to resting position.

Group 2 exercises include (feet

staggered Group):

1.Standing horizontal abduction

at 90˚ abduction

2.Standing horizontal abduction at

130˚ abduction

3.Standing external rotation

4.Standing extension

5.Bilateral shoulder external

rotation

6.Standing ER at 90˚ abduction

7.Standing rowing

1. The subject is positioned standing with the shoulder resting at 90˚ forward flexion and holds an elastic band. From this position, the subject

horizontally abducts the arm while maintaining the shoulder at 90˚ abduction with the shoulder in external rotation (thumb up) until the arm reached

the frontal plane. While performing this exercise, a therapist will initially verbally and tactilely cueing the subject to stand in a feet staggered

posture with the ipsilateral (relative to the test shoulder) foot placed 1 foot length posterior to the midline and maintain a constant scapular squeeze

while performing the exercise (staggered posture,

2. The subject is positioned standing with the shoulder resting at 90˚ forward flexion. From this position, the subject horizontally abducts the arm

while maintaining the shoulder at 130˚ abduction with the shoulder in external rotation (thumb up) until the arm reached the frontal plane. While

performing this exercise, a therapist will initially verbally and tactilely cueing the subject to stand in a feet staggered posture with the ipsilateral

(relative to the test shoulder) foot placed 1 foot length posterior to the midline and maintain a constant scapular squeeze while performing the

exercise (staggered posture,).

3. The subject is standing with the arm at the side with a towel between the elbow and rib cage. The subject then externally rotates the shoulder to 50

degrees above the horizontal then returns back to resting position. While performing this exercise, a therapist will initially verbally and tactilely

cueing the subject to stand in a feet staggered posture with the ipsilateral (relative to the test shoulder) foot placed 1 foot length posterior to the

midline and maintain a constant scapular squeeze while performing the exercise (staggered posture).

Table 11: Specific Therapeutic Exercises Descriptions and EMG activation (continued 1)

4. The subject is positioned standing with the arm resting at 90˚ forward flexion. The subject then extends the shoulder while keeping the hand in

supination (thumb pointing outward) until the arm reaches 5 degrees past the frontal plane then returns back to resting position. While performing

this exercise, a therapist will initially verbally and tactilely cueing the subject to stand in a feet staggered posture with the ipsilateral (relative to the

test shoulder) foot placed 1 foot length posterior to the midline and maintain a constant scapular squeeze while performing the exercise (staggered

posture,).

5. The subject is standing with a taut elastic band in the subjects hand with the palms facing each other. The subject then bilaterally externally rotates

the shoulder while maintaining the shoulder and elbow position past 50 degrees from the sagittal plane and then returns to the resting position.

While performing this exercise, a therapist will initially verbally and tactilely cueing the subject to stand in a feet staggered posture with the

ipsilateral (relative to the test shoulder) foot placed 1 foot length posterior to the midline and maintain a constant scapular squeeze while performing

the exercise (staggered posture,).

6. The subject is standing with the shoulder in 90˚ abduction and the elbow in 90˚ flexion the slight hand supination (thumb up). The subject then

extends the arm clearing the frontal plane then returns to the resting position. While performing this exercise, a therapist will initially verbally and

tactilely cueing the subject to stand in a feet staggered posture with the ipsilateral (relative to the test shoulder) foot placed 1 foot length posterior

to the midline and maintain a constant scapular squeeze while performing the exercise (staggered posture).

7. The subject is standing with the arm resting at 90˚ forward flexion and hand in supination (thumb facing laterally). The subject then extends the

shoulder and flexes the elbow simultaneously until the hand is parallel to the body. The subject then returns to resting position. While performing

this exercise, a therapist will initially verbally and tactilely cueing the subject to stand in a feet staggered posture with the ipsilateral (relative to the

test shoulder) foot placed 1 foot length posterior to the midline and maintain a constant scapular squeeze while performing the exercise (staggered

posture,).

Group 3 exercises include

(conscious correction Group):

1.Prone horizontal abduction at

90˚ abduction

2.Prone horizontal abduction at

130˚ abduction

3.Sidelying external rotation

4.Prone extension

5.Bilateral shoulder external

rotation

6.Prone ER at 90˚ abduction

7.Prone rowing

1. The subject is positioned prone with the shoulder resting at 90˚ forward flexion. From this position, the subject horizontally abducts the arm while

maintaining the shoulder at 90˚ abduction with the shoulder in external rotation (thumb up) until the arm reached the frontal plane. While

performing this exercise, a therapist will be verbally and tactilely cueing the subject to contract the lower trapezius (conscious correction).

2. The subject is positioned prone with the shoulder resting at 90˚ forward flexion. From this position, the subject horizontally abducts the arm while

maintaining the shoulder at 130˚ abduction with the shoulder in external rotation (thumb up) until the arm reached the frontal plane. While

performing this exercise, a therapist will be verbally and tactilely cueing the subject to contract the lower trapezius (conscious correction).

3. The subject is side lying with the arm at the side with a towel between the elbow and rib cage. The subject then externally rotates the shoulder to 50

degrees above the horizontal then returns back to resting position. While performing this exercise, a therapist will be verbally and tactilely cueing

the subject to contract the lower trapezius (conscious correction).

4. The subject is positioned prone with the arm resting at 90˚ forward flexion. The subject then extends the shoulder while keeping the hand in

supination (thumb pointing outward) until the arm reaches 5 degrees past the frontal plane then returns back to resting position. While performing

this exercise, a therapist will be verbally and tactilely cueing the subject to contract the lower trapezius (conscious correction,).

Table 11: Specific Therapeutic Exercises Descriptions and EMG activation (continued 2)

5. The subject is standing with a taut elastic band in the subjects hand with the palms facing each other. The subject then bilaterally externally rotates

the shoulder while maintaining the shoulder and elbow position past 50 degrees from the sagittal plane and then returns to the resting position.

While performing this exercise, a therapist will be verbally and tactilely cueing the subject to contract the lower trapezius (conscious correction,).

6. The subject is lying prone with the shoulder in 90˚ abduction and the elbow in 90˚ flexion the slight hand supination (thumb up). The subject then

lifts the arm off the mat in its entirety clearing the ulna and humerus from the mat then returns to the resting position. While performing this

exercise, a therapist will be verbally and tactilely cueing the subject to contract the lower trapezius (conscious correction).

7. The subject is lying prone with the arm resting at 90˚ forward flexion and hand in supination (thumb facing laterally). The subject then extends the

shoulder and flexes the elbow simultaneously until the hand is parallel to the body. The subject then returns to resting position. While performing

this exercise, a therapist will be verbally and tactilely cueing the subject to contract the lower trapezius (conscious correction,).

a normal posture without conscious correction or a staggered foot posture. Group 2 performed

specific therapeutic exercises with a staggered foot posture where the foot ipsilateral to the arm

performing the exercise is placed behind the frontal plane. Group 3 was comprised of specific

therapeutic exercises performed with a conscious posture correction by a physical therapist.

Phase 2 of the study involved individuals who had been diagnosed with shoulder impingement

and met the inclusion and exclusion criteria. Then each subject in phase 2 was randomized into

one of the three groups described above and shown in Table 11.

Group 1 exercises included (control Group, not altered posture): 1) prone horizontal

abduction at 90˚ abduction, 2) prone horizontal abduction at 130˚ abduction, 3) side lying

external rotation, 4) prone extension, 5) bilateral shoulder external rotation, 6) prone external

rotation at 90˚ abduction, and 7) prone rowing. Exercises for Group 2 included (feet staggered

Group): 1) standing horizontal abduction at 90˚ abduction, 2) standing horizontal abduction at

130˚ abduction, 3) standing external rotation, 4) standing extension, 5) bilateral shoulder

external rotation, 6) standing external rotation at 90˚ abduction, and 7) standing rowing. The

exercises Group 3 performed were (conscious correction Group): 1) prone horizontal abduction

at 90˚ abduction, 2) prone horizontal abduction at 130˚ abduction, 3) side lying external

rotation,

4) prone extension, 5) bilateral shoulder external rotation, 6) prone

external rotation at 90˚ abduction, 7) prone rowing (Table 11).

The phase 1 participants included 30 healthy adults (12 males and 18 females) with an

average height of 59.6 inches (range 52 to 72 inches), average weight of 149.37 pounds (range

115 to 220 pounds), and average of 22.57 years (range 18-49 years). In phase 2, participants

included 16 adults diagnosed with impingement and having an average height of 65.3 inches

(range 58 to 70 inches), average weight of 182.31 pounds (range 129 to 290 pounds), average

age of 47.44 years (range 19-65 years), and an average duration of symptoms of 12.81 months

(range 20 days to 10 years).

Muscle activity was measured in the dominant shoulder’s lower trapezius muscle using

surface electromyography (sEMG). Noraxon Ag–AgCl bipolar surface electrodes (Noraxon,

Arizona, USA) were placed over the belly of the lower trapezius using published placements

(Basmajian & DeLuca, 1995). The electrode position of the lower trapezius was placed

obliquely upward and laterally along a line between the intersection of the spine of the scapula

with the vertebral border of the scapula and the seventh thoracic spinous process (Figure 4).

Prior to electrode placement, the placement area was shaved and cleaned with alcohol to

minimize impedance with a ground electrode placed over the clavicle. EMG signals were

collected using a Noraxon MyoSystem 1200 system (Noraxon, Arizona, USA) 4 channel EMG

to collect data on a processing and analyzing computer program. The lower trapezius EMG

activity was collected during therapeutic exercises and the skin was prepared prior to electrode

placement by shaving hair (if necessary), abrading the skin with fine sandpaper, and cleaning

the skin with isopropyl alcohol to reduce skin impedance.

Figure 4: Surface electrode placement for lower trapezius muscle.

Data collection for each subject began by first recording the resting level of EMG

electrical activity. Post exercise EMG data was rectified and smoothed within a root mean square

in 150ms window and MVIC was normalized over a 500ms window. ECG reduction was also

used if ECG rhythm was present in the data.

During the protocol, EMG data was recorded over a series of three isometric contractions

selected to obtain the maximum voluntary isometric contraction (MVIC) of the lower trapezius

muscle tested and sustained for three seconds in positions specific to the muscle of interest

(Kendall, 2005)(Figure 5). The MVIC test consisted of manual resistance provided by the

investigator, a physical therapist, and a metronome used to control the duration of contraction.

Figure 5: The MVIC position for the lower trapezius was prone, shoulder in 125˚ of abduction

and the MVIC action will be resisted arm elevation.

All analyses were performed using SPSS statistics software (SPSS Science Inc, Chicago,

Illinois) with significance established at the p ≤ 0.05 level. A 3x7 repeated measures analysis of

variance (ANOVA) was used to test hypothesis. Mauchly's tests of sphericity were significant in

phase one and phase two, therefore the Huynh-Feldt correction for both phases. Tukey post-hoc

tests were used in phase one and phase two and least significant difference adjustment for

multiple comparisons were used in comparison of means.

3.3 RESULTS

Our data revealed no significant difference in EMG activation of the lower trapezius with

varying postures in phase one participants. Pairwise comparisons between Group 1 and Group 2

(p = .371) p Group 2 and Group 3 (p = .635, and Group 1 and Group 3 (p = .176 (Table 12).

However, statistical differences did exist between exercises. All exercises were

Table 12: Pairwise comparisons of the 3 Groups in phase 1

Comparison Significance

Group 1 v Group 2 .371

Group 3 .176

Group 2 v Group 3 .635

statistically significant from the others with the exceptions of exercise 1 and 6 for lower

trapezius activation (p=.323), exercise 3 and 5 (p=.783), and exercise 4 and 7 (p=.398). Also,

some exercises exhibited the highest EMG activity of the lower trapezius including exercises 2,

6, and 1. Exercise 2 exhibited 73.9% (Group 1), 88.9% (Group 2), and 73.6% (Group 3)

%MVIC EMG activation of the lower trapezius. Exercise 6 exhibited 58.5% (Group 1), 79.2%

(Group 2), and 47.9% (Group 3) %MVIC EMG activation of the lower trapezius. Lastly,

exercise 1 exhibited 59.7% (Group 1), 59.5% (Group 2), and 57.4% (Group 3) %MVIC EMG

activation of the lower trapezius. Overall exercise 2 exhibited the greatest EMG activation of the

lower trapezius.

Our data suggests no significant difference in EMG activation of the lower trapezius with

varying postures when comparing Group 1 to Group 2 (p =.161) and when comparing Group 3 to

Group 1 (p=.304) in phase two participants (Table 13). However a significant difference was

obtained when comparing Group 2 to Group 3 (p=.021). In general, Group 3 exhibited higher

Table 13: Pairwise comparisons of the 3 Groups in phase 2

Comparison Significance

Group 1 v Group 2 .161

Group 3 .304

Group 2 v Group 3 .021

EMG activity of the lower trapezius in every exercise when compared to Group 2. Also,

statistical differences existed between exercises. All exercises were statistically significant from

the others for lower trapezius activation with the exceptions of exercise 2 and 6 (p=.481),

exercise 3 and 4 (p=.270), exercise 3 and 5 (p=.408), and exercise 3 and 7 (p=.531). Also, some

exercises exhibited the highest %MVIC EMG activity of the lower trapezius including exercises

2, 6, and 1. Exercise 2 exhibited an average of 76.4% (Group 1), 55.3% (Group 2), and 80.1%

(Group 3) %MVIC EMG activation of the lower trapezius. Exercise 6 exhibited 80.3% (Group

1), 43.9% (Group 2), and 73% (Group 3) %MVIC EMG activation of the lower trapezius. Lastly,

exercise 1 exhibited 48.9% (Group 1), 39.3% (Group 2), and 60.8% (Group 3) %MVIC EMG

activation of the lower trapezius. Overall exercise 2 exhibited the greatest EMG activation of the

lower trapezius and Group 3 exhibited the highest percentage 80.1% (Table 14).

Table 14: Percentage of MVIC

exhibited by exercise 2 in all

Groups

Group 1 76.4%

Group 2 55.27%

Group 3 80.1%

3.4 DISCUSSION

Our data showed no differences between EMG activation in different postures in phase one

and phase two except for Groups 2 and 3 in phase two, which contradicted what other authors

have demonstrated (Reinold, et al., 2004; De Mey, et. al., 2013). In phase 2 however, Group 2

(feet staggered Group) performed standing resistance band exercises and Group 3 (conscious

correction Group) performed the exercises lying on a plinth while a physical therapist cued the

participant to contract the lower trapezius during repetitions. This gave some evidence to the

need for individuals, who have shoulder impingement, to have a supervised rehabilitation

program. While there was no statistical difference between Groups one and three in phase 2,

every exercise in Group 3 exhibited higher EMG activation of the lower trapezius than Groups 1

and 2 except for exercise 6 in Group 1 (Group 1=80%, Group 3=73%). While the data was not

statistically significant, it was important to note that this project looked at numerous exercises

which did made it more difficult to show a significant difference between Groups. This may

warrant further research looking at individual exercises with changed posture and the effect on

EMG activation.

When looking at the exercises which exhibited the highest EMG activation, phase one

exercise 2 exhibited the highest EMG activation in the participants 73.9% (Group 1), 88.9%

(Group 2), and 73.6% (Group 3) and there was no statistical difference between Groups. Phase

2 participants also exhibited a high EMG activation in the lower trapezius in exercise two 76.4%

(Group 1), 55.3% (Group 2), and 80.1% (Group 3). Overall this exercise showed to exhibited

the highest EMG activity of the lower trapezius which demonstrates its importance to activating

the lower trap during therapeutic exercises in rehabilitation patients. Prior research has

demonstrated the prone horizontal abduction at 135˚ with external rotation (97±16%MVIC;

Ekstrom, Donatelli, & Soderberg, 2003) to exhibit high EMG activity of the lower trapezius.

Therefore, in both phases the prone horizontal abduction at 130˚ with external rotation exercise

is the optimal exercise to activate the lower trapezius.

Exercise 6 also exhibited a high EMG activity of the lower trapezius in both phases. In phase

one, exercise 6 exhibited 58.5% (Group 1), 79.2% (Group 2), and .47.9% (Group 3) %MVIC

EMG activation of the lower trapezius and in phase two exercise 6 exhibited 80.3% (Group 1),

43.9% (Group 2), and 73% (Group 3) %MVIC EMG activation of the lower trapezius. Prior

research has demonstrated standing external rotation at 90˚ abduction (88±51%MVIC; Myers,

Pasquale, Laudner, Sell, Bradle, & Lephart, 2005) to have a high EMG activation of the lower

trapezius, which was comparable to the Group 2 postures in phase one (79.2%) and two (43.9%).

Both Groups seemed consistent in the findings of prior research on activation of the lower

trapezius.

Prior research has also demonstrated the prone external rotation at 90˚ abduction

(79±21%MVIC; Ekstrom, Donatelli, & Soderberg, 2003) exhibited high EMG activation of the

lower trapezius. This was comparable to exercise 6 in Group 1 (58.5%) and Group 3 (.47.9%) in

phase one and Group 1 (80.3%) and Group 3 in phase 2 (73%). Our results seemed comparable

to prior research on the EMG activation of this exercise. Exercise 1 also exhibited high-moderate

lower trapezius activation, which was comparable to prior research. In phase one, exercise 1

exhibited 59.7% (Group 1), 59.5% (Group 2), and 57.4% (Group 3) and in phase two exercise 1

exhibited 48.9% (Group 1), 39.3% (Group 2), and 60.8% (Group 3) EMG activation of the

lower trapezius. Prior research has demonstrated prone horizontal abduction at 90˚ abduction

with external rotation (74±21%MVIC; Ekstrom, Donatelli, & Soderberg, 2003)(63±41%MVIC;

Moseley, Jobe, Pink, Perry, & Tibone, 1992) exhibited moderate to high EMG activation, which

was comparable to phase one Group 1(59.7%), phase one Group 3(57.4%), phase two Group 1

(48.9%), and phase two Group 3(60.8%). Our results seemed comparable to prior research.

Inherent limitations existed using surface EMG (sEMG) since the point of attachment was a

mobile skin, and the skins mobility made it difficult to test over the same area in different

exercises. Another limitation was the possibility that some electrical activity originated from

other muscles not being studied, called crosstalk (Solomonow, et al., 1994). In this study,

subjects also had varying amounts of subcutaneous fat, which may have may have influenced

crosstalk in the sEMG amplitudes (Solomonow, et al., 1994; Jaggi, et al., 2009). Another

limitation included the fact that the phase two participants were currently in physical therapy and

possibly had performed some of the exercises in a rehabilitation program, which would have

increased their familiarity with the exercise as compared to phase one participants.

In weight selection determination, a standardization formula was used, which calculated the

weight for the individual, based on their anthropometrics. This limits the amount of

interpretation because individuals were not all performing at the same level of their % rep

maximum, which may decrease or increase the individuals strain level and alter EMG

interpretation. One reason for the lack of statistically significant differences may be due to the

participants were not performing a repetition maximum test and determining the weight to use

from a percentage of the one repetition max. This may have yielded higher EMG activation in

certain Groups or individuals. Also, fatiguing exertion may have caused perspiration or changes

in skin temperature which may have decreased the adhesiveness of electrodes and or skin

markers, where by altering EMG signals.

Intra-individual errors between movements and between Groups (healthy vs pathologic)

and intra-observer variance can also add variance to the results. Even though individuals in

phase 2 were screened for pain during the project, pain in the pathologic population may not

allow the individual to perform certain movements, which is a limitation specific to this

population.

3.5 CONCLUSION

In conclusion, the prone 130 of abduction with external rotation exercise demonstrated a

maximal %MVIC activation profile for the lower trapezius. Unfortunately, no differences were

displayed in the Groups to correlate a change in posture with an increase in EMG activation of

the lower trapezius; however, this may warrant further research which examines each exercise

individually.

3.6 ACKNOWLEDGEMENTS

I would like to acknowledge Dennis Landin for his help guidance in this project, Phil Page for

providing me with the tools to perform EMG analysis, and Peak Performance Physical Therapy

for providing the facilities for this project.

CHAPTER 4: THE EFFECT OF LOWER TRAPEZIUS FATIGUE ON SCAPULAR

DYSKINESIS IN INDIVIDUALS WITH A HEALTHY PAIN FREE SHOULDER

COMPLEX

4.1 INTRODUCTION

Subacromial impingement is used to describe a decrease in the distance between the

inferior border of the acromion and superior border of the humeral head and proposed

precursors include altered scapula kinematics or scapula dyskinesis. The proposed study

examined the effect of lower trapezius fatigue on scapular dyskinesis in a healthy male adult

population with a pain-free (dominant arm) shoulder complex. During the study, the subjects

were under the supervision and guidance of a licensed physical therapist while each individual

performed a fatiguing protocol on the lower trapezius, a passive stretching protocol on the lower

trapezius, and the individual was evaluated for scapular dyskinesis and muscle weakness before

and after the protocols.

Subacromial impingement is defined by a decrease in the distance between the inferior

border of the acromion and superior border of the humeral head (Neer, 1972). This has been

shown to cause compression and potential damage of the soft tissues including: the supraspinatus

tendon, subacromial bursa, long head of the biceps tendon, and the shoulder capsule (Bey, et al.,

2007; Flatow, et al., 1994; McFarland, et al., 1999; Michener, et al., 2003). This impingement,

often a precursor to rotator cuff tears, have been shown to result from either (1) superior humeral

head translation (2) altered scapular kinematics (Grieve & Dickerson, 2008), or a combination of

the two. The first mechanism, superior humeral translation, has been linked to rotator cuff

fatigue, (Chen, et al., 1999; Chopp, et al., 2010; Cote, et al., 2009; Teyhen, et al., 2008) and

confirmation has been attained radiographically following a generalized rotator cuff fatigue

protocol (Chopp, et al., 2010). The second previously proposed mechanism for impingement has

been altered scapular kinematics during movement. Individuals diagnosed with shoulder

impingement have exhibited muscle imbalances in the shoulder complex and specifically in the

force couple responsible for controlled scapular movements. The lower trapezius, upper

trapezius, and serratus anterior have been included as the target muscles in this force couple

(Figure 6).

Figure 6: Trapezius Muscles

During arm elevation in an asymptomatic shoulder, upward rotation, posterior tilt, and

retraction of the scapula have been demonstrated (Michener, et al., 2003). However, for

individuals diagnosed with subacromial impingement or shoulder dysfunction, these movements

have been impaired (Endo, et al., 2001; Lin, et al., 2005; Ludewig & Cook, 2000). Endo et al.

(2001) examined scapular orientation through radiographic assessment in patients with shoulder

impingement and healthy controls, taking radiographs at three angles of abduction: 0°, 45°, and

90°. Patients with unilateral impingement syndrome had significant decreases in upward rotation

and posterior tilt of the scapula compared to the contralateral arm, and these decreases were more

pronounced when the arm was abducted from neutral (0°). These decreases were absent in both

shoulders of healthy controls; thus changes seem related to impingement.

Prior research has demonstrated that shoulder external rotator muscle fatigue contributed

to altered scapular muscle activation and kinematics (Joshi, et al., 2011), but to this authors

knowledge, no prior articles have examined the effect of fatiguing the lower trapezius. The

lower trapezius and serratus anterior have been generally accepted as the scapular stabilizing

muscles, which have produced scapular upward rotation, posterior tilting, and retraction during

arm elevation. It has been anticipated that by functionally debilitating these muscles by means of

fatigue, changes in scapular orientation similar to impingement should occur. In prior shoulder

external rotator fatiguing protocols from pre-fatigue to post-fatigue, lower trapezius activation

decreased by 4% and scapular upward rotation motion increased in the ascending phase by 3°

while serratus activation remained unchanged from pre-fatigue to post-fatigue (Joshi, et al.,

2011). The authors concluded that alterations in the lower trapezius due to shoulder external

rotator muscle fatigue might predispose the shoulder to injury and has contributed to alterations

in scapula movements.

Scapular dysfunction or scapular dyskinesis has been defined as abnormal motion or

position of the scapula during motion (McClure, et al., 2009). These altered kinematics have

been caused by a shoulder injury such as impingement or by alterations in muscle force couples

(Forthomme, Crielaard & Croisier, 2008; Kolber & Corrao, 2011; Cools, et al., 2007). Kibler et

al. (2002) published a classification system for scapular dyskinesis for use during clinically

practical visual observation. This classification system has included three abnormal patterns and

one normal pattern of scapular motion. Type I pattern, characterized by inferior angle

prominence, has been present when increased prominence or protrusion of the inferior angle

(increased anterior tilting) of the scapula was noted along a horizontal axis parallel to the

scapular spine. Type II pattern, characterized by medial border prominence, has been present

when the entire medial border of the scapula was more prominent or protrudes (increased

internal rotation of the scapula) representing excessive motion along the vertical axis parallel to

the spine. Type III pattern, characterized by superior scapular prominence, has been present

when excessive upward motion (elevation) of the scapula was present along an axis in the

sagittal plane. Type IV pattern was considered to be normal scapulohumeral motion with no

excess prominence of any portion of the scapula and motion symmetric to the contralateral

extremity (Kibler, et al., 2002).

According to Burkhart et al., scapular dysfunction has been demonstrated in

asymptomatic overhead athletes (Burkhart, Morgan, & Kibler, 2003). Therefore, dyskinesis can

also be the causative factor of a wide array of shoulder injuries not only a result. Of particular

importance, the lower trapezius has formed and contributed to a force couple with other shoulder

muscles and the general consensus from current research has stated that lower trapezius

weakness has been a predisposing factor to shoulder injury although little data has demonstrated

this theory (Joshi, et al., 2011; Cools, et. al., 2007) However, one study has demonstrated that

scapula dyskinesis can occur in asymptomatic shoulders of competitive swimmers during a

training session (Madsen, Bak, Jensen, & Welter, 2011). Previous authors (Madsen, et al., 2011)

have demonstrated that training fatigue can induce scapula dyskinesis in healthy adults without

shoulder problems and current research has stated that the lower trapezius can predispose and

individual to injury and scapula dyskinesis. However, limited data has reinforced this last claim,

and current research has lacked information as to what qualifies as weakness or strength.

Therefore, the purpose of this study was to look at asymptomatic shoulders for lower trapezius

weakness using hand held dynamometry and scapula dyskinesis due to a fatiguing and stretching

protocol.

Our aim therefore was to determine if strength, endurance, or stretching of the lower

trapezius will have an effect on inducing scapula dyskinesis. The purpose of the study is to

identify if fatigue or stretching can cause scapula dyskinesis in healthy adults and predispose

individuals to shoulder impingement. We based a fatiguing protocol on prior research which has

shown to produce known scapula orientation changes (Chopp, et al., 2010; Tsai, et al., 2003)

and on prior research and studies which have shown exercises with a high EMG activity profile

of the lower trapezius (Coulon & Landin, 2014). Previous studies have consistently

demonstrated that an acute bout of stretching reduces force generating capacity (Behm, et al.,

2001; Fowles, et al., 2000; Kokkonen, et al., 1998; Nelson, et al., 2001), which led us in the

present investigation to hypothesize that such reductions would translate to an increase in

muscle fatigue.

This study has helped address two currently open questions. First, we have demonstrated

if lower trapezius fatigue can induce scapula dyskinesis in healthy individuals as classified by

Kibler’s classification system. Second, we have provided more clarity over which mechanism

(superior humeral translation or altered scapular kinematics) dominates changes in the

subacromial space following fatigue. Lastly, we have determined if there is a difference in

fatigue levels after a stretching protocol or resistance training protocol and if either causes

scapula dyskinesis.

4.2 METHODS

The proposed study examined the effect of lower trapezius fatigue on scapular dyskinesis

in 15 healthy males with a pain-free (dominant arm) shoulder complex. During the study, the

subjects were under the supervision and guidance of a licensed physical therapist with each

individual performing a fatiguing protocol on the lower trapezius, a passive stretching protocol

on the lower trapezius, and an individual evaluation for scapular dyskinesis and muscle

weakness

before and after the protocols. The exercise consisted of an exercise (prone horizontal abduction

at 130˚ of abduction) specifically selected since it exhibited high EMG activity in the lower

trapezius from prior work (Coulon & Landin, 2012) and research (Ekstrom, Donatelli, &

Soderberg, 2003)(Figure 7).

STUDY EMG activation (%MVIC)

Coulon & Landin, 2012 80.1%

Ekstrom, Donatelli, & Soderberg,

2003

97%

Figure 7: EMG activation of the lower trapezius during the prone horizontal abduction at 130˚ of

abduction

The stretching protocol consisted of a passive stretch which attempted to increase the

distance from the origin (spinous process T7-T12 vertebrae) to the insertion (spine of the

scapula) as previously described (Moore & Dalley, 2006). There were a minimum of ten days

between protocols if the fatiguing protocol was performed first and three days between protocols

if the stretching protocol was performed first. The extended amount of time was given for the

fatiguing protocol since delayed onset muscle soreness has been demonstrated to cause a

detrimental effect of the shoulder complex movements and force production and prior research

has shown these effects have resolved by ten days (Braun & Dutto, 2003; Szymanski, 2001;

Pettitt, et al., 2010).

Upon obtaining consent, subjects were familiarized with the perceived exertion scale

(PES) and rated their pretest level of fatigue. Subjects were instructed to warm up for 5 minutes

at resistance level one on the upper body ergometer (UBE). After the subject completed the

warm up, the lower trapezius isometric strength was assessed using a hand held dynamometer

(microFET2, Hoggan Scientific LLC, Salt Lake City, UT). The isometric hold was assessed 3

times and the average of the 3 trials was used as the pre-fatigue strength score. The isometric

hold position used for the lower trapezius has been described in prior research (Kendall, et al.,

2005)(Figure 8) and the handheld dynamometer was attached to a platform device, which the

subject pushed into at a specific point of contact.

Figure 8: The MMT position for the lower trapezius will be prone, shoulder in 125-130˚ of

abduction and the action will be resisted arm elevation against device (not shown).

A lever arm measurement of 22 inches was taken from the acromion to the wrist for each

individual and was the point of contact for isometric testing. Following dynamometry testing, a

visual observation classification system was used to classify the subject’s pattern of scapular

dyskinesis (Kibler, et al., 2002). Subjects were then given instructions on how to perform the

prone horizontal abduction at 130˚ exercise. In this exercise, the subject was positioned prone

with the shoulder resting at 90˚ forward flexion. From this position, the subject horizontally

abducted the arm while maintaining the shoulder at 130˚ abduction (as measured by a licensed

physical therapist with a goniometric device) with the shoulder in external rotation (thumb up)

until the arm reached the frontal plane (Figure 9).

Figure 9: Prone horizontal abduction at 130˚ abduction (goniometric device not pictured)

This exercise was designed to isolate the lower trapezius muscle and was therefore used

to facilitate fatigue of the lower trapezius. The percent of MVIC and EMG profile of this

exercise is 97% for lower trapezius, 101% middle trapezius, 78% upper trapezius, and 43%

serratus anterior (Ekstrom, Donatelli, & Soderberg, 2003). Data collection for each subject

began with a series of three isometric contractions of which the average was determined and a

scapula classification system and lateral scapular glide test allowed for scapula assessment and

was performed before and after each fatiguing protocol.

Once the subjects were comfortable with the lower trapezius exercise, they were then

instructed to complete this exercise for two minutes at a rate of 30 repetitions per minute

(metronome assisted) using a dumbbell weight and maintaining a scapular squeeze. Each subject

performed repetitions of each exercise with the speed of the repetition regulated by the use of a

metronome set to 60 beats per minute. The subject performed each concentric and eccentric

phase of the exercise during two beats. The repetition rate was set by a metronome and all

subjects used a weighted resistance 15%-20% of their average maximal isometric hold

assessment. Subjects were asked to rate their level of fatigue using the PES after the 2 minutes

(Figure 10) and were given max encouragement during the exercise.

Figure 10: Perceived Exertion Scale (PES) (Adapted from Borg, 1998)

The subjects were then given a one minute rest period before performing the exercise for

another two minutes. This process was repeated until they could no longer perform the exercise

and reported a 20 on the PES. This fatiguing activity is unilateral and once fatigue was reached,

the subject’s lower trapezius isometric strength was again assessed using a hand held

dynamometer. The isometric hold was assessed three times and the average of the three trials

was used as the post-fatigue strength. Then the scapula classification system and lateral scapula

slide test were assessed again.

The participants of this study had to meet the inclusion/exclusion criteria. The inclusion

criteria for all subjects were: 1) 18-65 years old, and 2) able to communicate in English. The

exclusion criteria of the healthy adult Group included: 1) recent history (less than 1 year) of a

musculoskeletal injury, condition, or surgery involving the upper extremity or the cervical spine,

and 2) a prior history of a neuromuscular condition, pathology, or numbness or tingling in either

upper extremity. Subjects were also excluded if they exhibited any contraindications to exercise

(Table 15).

Table 15: Contraindications to exercise

1. a recent change in resting ECG suggesting significant ischemia

2. a recent myocardial infarction (within 7 days),

3. an acute cardiac event

4. unstable angina

5. uncontrolled cardiac dysrhythmias

6. symptomatic severe aortic stenosis

7. uncontrolled symptomatic heart failure

8. acute pulmonary embolus or pulmonary infarction

9. acute myocarditis or pericarditis

10. suspected or known dissecting aneurysm

11. acute systemic infection accompanied by fever, body aches,

or swollen lymph glands.

Participants were recruited from Louisiana State University students, pre-physical

therapy students, and healthy individuals willing to volunteer. Participants filled out an informed

consent, PAR-Q, HIPAA authorization agreement, and met the inclusion and exclusion criteria

through the use of a verbal questionnaire. Each participant was blinded from the expected

outcomes and hypothesized outcome of the study. Data was processed and the study will look at

differences in muscle force production, scapula slide test, and scapula dyskinesis classification.

Fifteen males participated in this study and data was collected from their dominant upper

extremity (13 right and 2 left upper extremities). Sample size was determined by a power

analysis using the results from previous studies (Chopp, et al., 2011; Noguchi, et al., 2013);

fifteen participants were required for adequate power. The mean height, weight, and age were

69.27 inches (range 66 to 75), weight 175.8 pounds (range 150 to 215), and age 24.67 years

(range 20 to 57 years), respectively. Participants were excluded from the study if they reported

any upper extremity pain or injury within the past year, or any bony structural damage (humeral

head, clavicle or acromion fracture, or joint dislocation). The study was approved by the

Louisiana State University Institutional Review Board, and each participant provided informed

consent.

The investigators conducted the assessment for the inclusion and exclusion criteria

through the use of a verbal questionnaire and PAR-Q. The study was explained to all subjects

and they read and signed the informed consent agreement approved by the university

institutional review board. On the first day of testing, the subjects were informed of their rights

and procedures of participating in this study, discussed and signed the informed consent, read

and signed the HIPPA authorization, discussed inclusion and exclusion criteria, received a brief

screening examination, and were oriented to the testing protocol.

The fatiguing protocol was sequenced as follows: pre-fatigue testing, practice and

familiarization, two minute fatigue protocol and one minute rest (repeated), post-fatigue testing.

The stretching protocol was sequenced as follows: pre-stretch testing, practice and

familiarization, manually stretch protocol (three stretches for 65 seconds each), one min rest

(after each stretch), and post-stretch testing. In total the individual was tested over two test

periods, with a minimum of ten days between protocols if the fatiguing protocol was performed

first and three days between protocols if the stretching protocol was performed first. The

extended amount of time was given for the fatiguing protocol since delayed onset muscle

soreness may cause a detrimental effect of the shoulder complex movements and force

production and prior research has shown these effects have resolved by ten days (Braun & Dutto,

2003; Szymanski, 2001).

The fatiguing protocol consisted of five parts: (1) pre-fatigue scapula kinematic

evaluation, (2) muscle-specific maximum voluntary contractions, used to determine repetition

max and weight selection, (3) scaling of a weight used during the fatiguing protocol, (4) a prone

horizontal abduction at 130˚ fatiguing task, and (5) post-fatigue scapula kinematic evaluation.

The stretching protocol consisted of four parts: (1) pre-stretch scapula kinematic evaluation, (2)

muscle-specific maximum voluntary contractions, (3) a manual lower trapezius stretch

performed by a physical therapist performed in prone, and (5) post-stretch scapula kinematic

evaluation.

Participants performed three repetitions of lower trapezius muscle-specific maximal

voluntary contractions (MVCs) against a stationary device using a hand held dynamometer

(microFET2, Hoggan Scientific LLC, Salt Lake City, UT). Two minute rest periods were

provided between each exertion to reduce the likelihood of fatigue (Knutson, et al., 1994; Chopp,

et al., 2010) and the MVC were preformed prior to and after the stretching and fatigue protocols.

During the fatiguing protocol, participants held a weight in their hand (determined to be between

15%-20% of MVC) with their thumb facing up and a tight grip on the dumbbell.

Pre-fatigue trials consisted of obtaining MVC test levels during isometric holds and

scapular evaluation/orientation measurements at varying humeral elevation angles and during

active elevation. Data was later compared to post-fatigue trials. To avoid residual fatigue from

MVCs, participants were given approximately five minutes of rest prior to the pre-fatigue

measurements.

The fatiguing protocol consisted of a repeated voluntary movement of prone horizontal

abduction at 130˚ repeated until exhaustion. The task consisted of repetitively lifting a dumbbell

with thumb up and a firm grip on dumbbell weight from 90˚ shoulder flexion with 0˚ elbow

flexion to 180˚ shoulder flexion with 0˚ elbow flexion at a controlled speed of 60 bpm

(controlled by metronome) until fatigued. The subject performed each task for two minutes and

the subjects were given a one minute rest period before performing the task for another two

minutes. The subject repeated the process until the task could no longer be performed and the

subject reported a 20 on the PES. The subject performed the fatiguing activity unilateral and

once fatigue was reached, the subject’s lower trapezius isometric strength was assessed using a

hand held dynamometer. The isometric hold was assessed three times and the average of the

three trials was used as the post-fatigue strength. The subject was also classified with the

scapular dyskinesis classification system and data was analyzed. All arm angles during task

were positioned by the experimenter using a manual goniometer.

During the protocol, verbal coaching and max encouragement were continuously

provided by the researcher to promote scapular retraction and subsequent scapular stabilizer

fatigue. Fatigue was monitored using a Borg Perceived Exertion Scale (PES)(Borg, 1982). The

participants verbally expressed the PES prior to and after every two minute fatiguing trial during

the fatiguing protocol. Participants continued the protocol until “failure” as determined by prior

scapular retractor fatigue research (Tyler, et al., 2009; Noguchi, et al., 2013). The subject was

considered in failure when the subject verbally indicated exhaustion (PES of 20), the subject

demonstrated and inability to maintain repetitions at 60 bpm, the subject demonstrated an

inability to retract the scapula completely before exercise on three consecutive repetitions, and

the subject demonstrated the inability to break the frontal plane at the cranial region with the

elbow on three consecutive repetitions.

Fifteen healthy male adults without shoulder pathology on their dominant shoulder

performed the stretching protocol. Upon obtaining consent, subjects were familiarized with the

perceived exertion scale (PES) and asked to rate their pretest level of fatigue. Subjects were

instructed to warm up for five minutes at resistance level one on the upper body ergometer

(UBE). After the warm up was completed, the examiner assessed the lower trapezius isometric

strength using a hand held dynamometer (microFET2, Hoggan Scientific LLC, Salt Lake City,

UT). The isometric hold was assessed three times and the average of the three trials indicated the

pre-fatigue strength score. The isometric hold position used for the lower trapezius is described

in prior research (Kendall et al, 2005); the handheld dynamometer was attached to a platform

and the subject then pushed into the device. Prior to dynamometry testing, a visual observation

classification system classified the subject’s pattern of scapular dyskinesis (Kibler, et al., 2002).

Subjects were then manually stretched which attempted to increase the distance from the origin

(spinous process of T7-T12 thoracic vertebrae) to the insertion (spine of the scapula) as

previously described (Moore & Dalley, 2006). The examiner performed three passive stretches

and held each for 65 seconds since only long duration stretches (>60 s) performed in a pre-

exercise routine have been shown to compromise maximal muscle performance and are

hypothesized to induce scapula dyskinesis. The examiner performed the stretching activity

unilaterally and once performed the subject’s lower trapezius isometric strength was assessed

using a hand held dynamometer. The isometric hold was assessed 3 times and the average of the

3 trials was then used as the post-stretch strength. Lastly, the subject was classified into the

scapular dyskinesis classification system and all data will be analyzed.

Post-fatigue trials were collected using an identical protocol to that described in pre-

fatigue trials. In order to prevent fatigue recovery confounding the data, the examiner

administered post-fatigue trials immediately after completion of the fatiguing or stretching

protocol.

When evaluating the scapula, the examiner observed both the resting and dynamic

position and motion patterns of the scapula to determine if aberrant position or motion was

present (Magee, 2008; Ludewig & Reynolds, 2009; Wright, et al., 2012). This classification

system (discussed earlier in this paper) consisted of three abnormal patterns and one normal

pattern of scapular motion. (Kibler, et al., 2002). The examiner used two observational methods.

First determining if the individual demonstrated scapula dyskinesis with the YES/NO method

and secondary determining what type the individual demonstrated (type I-type IV). The

sensitivity (76%), inter-rater agreement (79%), and positive predictive value (74%) have all been

documented (Kibler, et al., 2002). The second method used was the lateral scapula slide test, a

semi-dynamic test used to evaluate scapular position and scapular stabilizer strength. The test is

performed in three positions (arms at side, hands-on-hips, 90˚ glenohumeral abduction with full

internal rotation) measured (cm) from the inferior angle of the scapula to the spinous process in

direct horizontal line. A positive test consisted of greater than 1.5cm difference between sides

and indicated a deficit in dynamic stabilization or postural adaptations. The ICC (.84) and inter-

tester reliability (.88) have been determined for this test (Kibler, 1998).

A paired-sample t-test was used to determine differences in lower trapezius muscle

testing and stretching between pre-fatigue and post-fatigue conditions. All analyses were

performed using Statistical Package for Social Science Version 12.0 software (SPSS, Inc,

Chicago, IL). An alpha level of .05 probability was set a priori to be considered statistically

significant.

4.3 RESULTS

Data suggested a statistically significant difference between the fatigue and stretching

Group (p=.002). The stretching Group exhibited no scapula dyskinesis pre-stretching protocol

and post-stretching protocol in the scapula classification system or the 3 phases of the scapula

slide test (arms at side, hands on hips, 90˚ glenohumeral abduction with full humeral internal

rotation). However, a statistically significant difference (p<.001) was observed in the pre-stretch

MVC test (25.1556 pounds) and post-stretch MVC test (24.5556 pounds). This is a 2.385%

decrease in force production after stretching.

In the pre-testing of the pre-fatigue Group, all participants exhibited no scapula

dyskinesis in the Yes/No classification system and all exhibited type IV scapula movement

pattern prior to fatigue protocol. All participants were negative for the three phases of the

scapula slide test (arms at side, hands on hips, 90˚ glenohumeral abduction with full humeral

internal rotation) with the exception of one participant who had a positive result on the 90˚

glenohumeral abduction with full humeral internal rotation part of the test. During testing, this

participant did report he had participated in a fitness program prior to coming to his assessment.

Our data suggests a statistically significant difference (p<.001) in pre-fatigue MVC

(25.2444 pounds) and post-fatigue MVC (16.5333 pounds). This is a 34.5% decrease in force

production, and all participants exhibited a decrease in average MVC with a mean of 16.533

pounds. There was also a statistically significant difference in mean force production pre- and

post- fatiguing exercise (p=<.001) demonstrating the individuals exhibited true fatigue. In the

post-fatigue trial all but four of the participants were classified as yes (73.3%) for scapula

dyskinesis and the post fatigue dyskinesis types were type I (6; 40%), type II (5; 33.33%), type

III (0), and type IV (4; 26.67%). All participants were negative for the arms at side phase of the

scapula slide test except for participants 4,6,10,11,12, and 14 (6; 40%). All participants were

negative for the hands on hips phase of the scapula slide test except participants 4, 6, 9, and 10

(4; 26.67%). All participants were negative for the 90˚ glenohumeral abduction with full

humeral internal rotation phase of the scapula slide test with the exception of participants 1, 2, 3,

4, 7, 8, 9, 10, 12, 13, and 14 (10; 66.67%).

The average number of fatiguing trials each participant completed was 8.466 with the

lowest being four trials and the longest being sixteen trials. The average weight used based on

MVC was 4.6 pounds with the lowest being four pounds and the highest being seven pounds.

4.4 DISCUSSION

In this study, the participants exhibited scapula dyskinesis with an exercise specifically

selected to fatigue the lower trapezius. The results agreed with prior research, which has shown

significant differences in scapula upward rotation and posterior tilt for 0 to 45 degrees and 45 to

90 degrees of elevation (Chopp, Fischer, & Dickerson, 2010). The presence of scapula

dyskinesis gives some evidence that fatigue of the lower trapezius had a detrimental effect on

shoulder function and possibly leads to shoulder pathology. Also, these results demonstrated

that proper function and training of the lower trapezius is vitally important for overhead

athletes and shoulder health.

With use of the classification system, an investigator bias was possible since the same

participants and tester participated in both sessions. Also, the scapula physical examination test

have demonstrated a moderate level of sensitivity and specificity (Table G in Appendix) with

prior research finding sensitivity measurements from 28-96 depending on position and

specificity measurements ranging from 4-58.

The results of our study have also demonstrated relevance for shoulder rehabilitation and

injury-prevention programs. Fatigue induced through repeated overhead glenohumeral

movements while in external rotation resulted in altered strength and endurance in the lower

trapezius muscle and in scapular dyskinesis, and has been linked to many injuries, including

subacromial impingement, rotator cuff tears, and glenohumeral instability. Addressing

imbalances in the lower trapezius through appropriate exercises is imperative for establishing

normal shoulder function and health.

4.5 CONCLUSION

In conclusion, lower trapezius fatigue appeared to contribute or even caused scapula

dyskinesis after a fatiguing task, which could have identified a precursor to injury in repetitive

overhead activities. This demonstrated the importance of addressing lower trapezius endurance,

especially in overhead athletes, and the possibility that lower trapezius is the key muscle in

rehabilitation of scapula dyskinesis.

CHAPTER 5: SUMMARY AND CONCLUSIONS

In summary, shoulder impingement has been identified as a common problem in the

orthopedically impaired population and scapula dyskinesis is involved in this pathology. The

literature has been uncertain as to the causative factor of scapula dyskinesis in shoulder

impingement and no links have been demonstrated as to the specific muscle contributing to the

biomechanical abnormality. These studies attempted to demonstrate therapeutic exercises which

specifically activate the lower trapezius and use the appropriate exercise to fatigue the lower

trapezius and induce scapula dyskinesis.

The first study demonstrated that healthy individuals and individuals diagnosed with

shoulder impingement can maximally activate the lower trapezius with a specific prone shoulder

exercise (prone horizontal abduction at 130˚ with external rotation). This knowledge

demonstrated an important finding in the application of rehabilitation exercise prescription in

shoulder pathology and scapula pathology. The results from the second study demonstrated the

importance of the lower trapezius in normal scapula dynamic movements and the important

muscles contribution to scapula dyskinesis. Interestingly, lower trapezius fatigue was a causative

factor in initiating scapula dyskinesis and possibly increased the risk of injury. Applying this

knowledge to clinical practice, a clinician might have assumed that lower trapezius endurance

may be a vital component in preventing injuries in overhead athletes. This might lead future

injury prevention studies to examine the effect of a lower trapezius endurance program on

shoulder injury prevention.

Also, the results of this research have allowed further research to specifically target

rehabilitation protocols in scapula dyskinesis which determine if addressing the lower trapezius

may abolish scapula dyskinesis and prevent future shoulder pathology. This would be a

groundbreaking discovery since no other studies have demonstrated appropriate rehabilitation

protocols for scapula dyskinesis and no research articles have demonstrated a cause effect

relationship to correct the abnormal movement pattern.

Lower Trapezius Muscle Contribution to Shoulder Impingement and Scapular Dyskinesis

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