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    journal o orthopaedic & sports physical therapy | volume 39 | number 2 | ebruary 2009 | 105

    [ CLINICAL COMMENTARY ]

    1Coordinator o Rehabilitation Research and Education, Department o Orthopedic Surgery, Division o Sports Medicine, Massachusetts General Hospital, Boston, MA; Rehabilitation

    Coordinator/Assistant Athletic Trainer, Boston Red Sox Baseball Club, Boston, MA. 2Proessor, Department o Physical Therapy, Caliornia State University, Sacramento, Sacramento,

    CA. 3Clinical Director, Champion Sports Medicine, Director o Rehabilitative Research, American Sports Medicine Institute, Birmingham, AL. Address correspondence to Dr Michael

    M. Reinold, Rehabilitation Coordinator/Assistant Athletic Trainer, Boston Red Sox Baseball Club, Fenway Park, 4 Yawkey Way, Boston, MA 02215. Email: [email protected]

    MICHAEL M. REINOLD, PT, DPT, ATC, CSCSH7

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    [ CLINICAL COMMENTARY ]

    toid activity (minimizing subacromial

    impingement).6,8,9,21,34,50,60,65,74 In addi-

    tion, rotator cuf muscles are requently

    treated either conservatively or surgically

    secondary to injuries.Exercise designed to strengthen the

    muscles o the rotator cuf are oten pre-

    scribed to patients with pathologies such

    as subacromial impingement. During

    scapular plane abduction in healthy sub-

    jects, the humeral head translates 1 to 3

    mm in the superior direction rom 0 to

    30 o abduction, slightly ineriorly rom

    30 to 60 o abduction, and in the su-

    perior or inerior direction during 60 to

    90 o abduction.26,50,67 Other data dem-

    onstrate that, during passive scapular

    plane abduction, the humeral head trans-

    lates superiorly 0.6 to 1.8 mm between

    0 to 150.25,26 But during active scapular

    plane abduction the humeral head re-

    mains nearly centered in the glenoid os-

    sa throughout the range o movement.26

    These data illustrate the importance o

    rotator cuf strength and muscle balance

    to resist humeral head superior transla-

    tion and help center the humeral head

    within the glenoid ossa during shoulder

    elevation.74 With rotator cuf pathology,

    altered kinematics and muscle activ-

    ity are present,31 and superior humeral

    head translation increases and subacro-

    mial space decreases.24 Moreover, during

    scapular plane shoulder abduction rom

    30 to 90, inraspinatus and subscapu-

    laris activity was ound to be significantly

    less in individuals with subacromial im-

    pingement compared to those without

    impingement.68

    Subjects with shoulder laxity and in-

    stability have also been shown to have

    altered kinematics and firing patterns othe rotator cuf.7,35,45,46,55,64,72 Compared to

    healthy subjects, patients with general-

    ized joint laxity demonstrated increased

    subscapularis activity during internal

    rotation (IR) exercise and decreased su-

    praspinatus and subscapularis activity

    during external rotation (ER) exercise.7,43

    Compared to healthy subjects, those with

    anterior instability exhibited less su-

    praspinatus activity between 30 to 60

    o shoulder elevation during abduction

    and scaption exercises.59

    These EMG data clearly illustrate

    aberrant muscle-firing patterns in in-

    dividuals with shoulder pathology. It isoten the goal o rehabilitation special-

    ists to prescribe exercises to normalize or

    prevent these abnormal firing patterns.

    Proper selection o exercises to activate

    muscle unction or each muscle o the

    rotator cuf should be considered during

    rehabilitation.

    IkfhWif_dWjkiThe supraspinatus compresses, abducts,

    and generates a small ER torque to the

    glenohumeral joint. Supraspinatus activi-

    ty increases as resistance increases during

    abduction/scaption movements, peaking

    at 30 to 60 o elevation or any given

    resistance. At lower elevation angles, su-

    praspinatus activity increases, providing

    additional humeral head compression

    within the glenoid ossa to counter the

    humeral head superior translation occur-

    ring with contraction o the deltoid.1 Due

    to a decreasing moment arm with abduc-

    tion, the supraspinatus is a more efective

    abductor in the scapular plane at smaller

    abduction angles.34,50,65

    Relatively high supraspinatus activity

    has been measured in several common

    rotator cuf exercises3,5,17,33,54,63,70,75,79,87

    and in several exercises that are not

    commonly thought o as rotator cuf ex-

    ercises, such as standing orward scap-

    ular punch, rowing exercises, push-up

    exercises, and 2-hand overhead medi-

    cine ball throws.13,17,32,81 These results

    suggest the importance o the rotator

    cuf in providing dynamic glenohumeral

    stability by centering the humeral headwithin the glenoid ossa during all up-

    per extremity unctional movements.

    This is an important concept or the

    clinician to understand. The muscles

    ability to generate abduction torque in

    the scapular plane appears to be great-

    est with the shoulder in neutral rotation

    or in slight IR or ER.50,65 This biome-

    chanical advantage has led to the devel-

    opment o exercises in the plane o the

    scapula to specifically strengthen the

    supraspinatus.38

    Jobe38 was the first to recommend ele-

    vation in the scapular plane (30 anterior

    to the rontal plane) with glenohumer-al IR, or the empty can exercise, to

    strengthen the supraspinatus muscle.

    Other authors37,40,66,69,70,77have suggested

    the ull can position, or elevation in the

    scapular plane with glenohumeral ER,

    to best strengthen and test the supraspi-

    natus muscle. Furthermore, compared

    to the empty can exercise, Blackburn5

    reported significantly greater supraspi-

    natus activity during prone horizontal

    abduction at 100 with ull ER, or prone

    ull can, position. The results o studies

    comparing these exercises provide in-

    consistent results due to methodological

    limitations, including lack o statistical

    analysis,38,79 lack o data or all 3 exercis-

    es,40,54,79,87and absence o data on deltoid

    muscle activity.87

    Recently, Reinold et al69 comprehen-

    sively evaluated the EMG signal o the

    supraspinatus and deltoid musculature

    during the ull can, empty can, and

    prone ull can exercises in an attempt

    to clariy the muscular activation during

    these exercises. The results showed that

    all 3 exercises provide a similar amount

    o supraspinatus activity ranging rom

    62% to 67% o maximal voluntary iso-

    metric contraction (MVIC). However,

    the ull can exercise demonstrated a

    significantly lower amount o middle

    and posterior deltoid activity compared

    to the 2 other exercises. This is clinically

    significant when trying to strengthen

    the supraspinatus while simultaneously

    minimizing potentially disadvanta-

    geous superior sheer orce due to del-toid activity.

    In patients with shoulder pain,

    weakness o the rotator cuf, or ine-

    ficient dynamic stabilization, it is the

    authors opinion that activities that

    produce higher levels o deltoid activ-

    ity in relation to supraspinatus activity,

    such as the empty can and prone ull

    can exercise, may be detrimental. This

    is due to the increased amount o supe-

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    journal o orthopaedic & sports physical therapy | volume 39 | number 2 | ebruary 2009 | 107

    rior humeral head migration that may

    be observed when the rotator cuf doesnot adequately compress the humerus

    within the glenoid ossa to counteract,

    or oppose, the superior pull o the del-

    toid (

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    [ CLINICAL COMMENTARY ]

    until it is about 1.3 cm at 60 abduction.65

    These data imply that the inraspinatus is

    a more efective external rotator at lower

    shoulder abduction angles. The teres mi-

    nor has a relatively constant ER momentarm (approximately 2.1 cm) and the abil-

    ity to generate torque throughout shoul-

    der abduction movement, which implies

    that shoulder abduction angle does not

    afect the efectiveness o the teres minor

    to generate ER torque.65

    Several studies have been designed to

    test the results o the model; but, as in

    studies on the supraspinatus, variations

    in experimental methodology have result-

    ed in conflicting results and controversy

    in exercise selection.3,5,17,19,27,33,44,54,63,70,77,79,81

    Several exercises have been recommend-

    ed based on EMG data, including shoul-

    der ER in the side-lying,3,70,79 standing,27,70

    or prone3,70 positions perormed at 0,3,70

    45,27,70 and 903,70 o abduction. Another

    exercise that has been shown to generate

    a high EMG signal o the inraspinatus

    and teres minor is prone horizontal ab-

    duction with ER.5,79

    Reinold et al70 analyzed several di-

    erent exercises commonly used to

    strengthen the shoulder external rota-

    tors to determine the most efective

    exercise and position to recruit muscle

    activity o the posterior rotator cuf. The

    authors report that the exercise that elic-

    ited the most combined EMG signal or

    the inraspinatus and teres minor was

    shoulder ER in side-lying (inraspina-

    tus, 62% maximal voluntary isometric

    contraction [MVIC]; teres minor, 67%

    MVIC), ollowed closely by standing ER

    in the scapular plane at 45 o abduction

    (inraspinatus, 53% MVIC; teres minor,

    55% MVIC), and finally prone ER in the90 abducted position (inraspinatus,

    50% MVIC; teres minor, 48% MVIC).

    Exercises in the 90 abducted posi-

    tion are oten incorporated to simulate

    the position and strain on the shoulder

    during overhead activities such as throw-

    ing. This position produced moderate

    activity o the external rotators but also

    increased activity o the deltoid and su-

    praspinatus. It appears that the amount

    o inraspinatus and teres minor activity

    progressively decreases as the shoulder

    moves into an abducted position, while

    activity o the supraspinatus and deltoid

    increases. This suggests that as the armmoves into a position o increased vulner-

    ability away rom the body, the supraspi-

    natus and deltoid are active to assist in

    the ER movement, while providing some

    degree o glenohumeral stability through

    muscular contraction.

    While standing ER exercises per-

    ormed at 90 o shoulder abduction may

    have a unctional advantage over exercis-

    es perormed at 0 o shoulder abduction

    or perormed in the scapular plane, due

    to the close replication in sporting activi-

    ties, the combination o shoulder abduc-

    tion and ER places strain on the shoulder

    capsule, particularly the anterior band o

    the inerior glenohumeral ligament.30,85,86

    The clinician must careully consider this

    when designing programs or patients

    with capsulolabral pathology.

    Side-lying ER may be the optimal ex-

    ercise to strengthen the external rotators

    based on the previously mentioned stud-

    ies. The inclusion o this exercise should

    be considered in all exercise programs

    attempting to increase ER strength or

    decrease capsular strain.

    Theoretically, ER perormed at 0 o

    shoulder abduction with a towel roll be-

    tween the rib cage and the arm provides

    both the low capsular strain and also a

    good balance between the muscles that

    externally rotate the arm and the muscles

    that adduct the arm to hold the towel.

    Our clinical experience has shown that

    adding a towel roll to the ER exercise

    provides assistance to the patient by en-

    suring that proper technique is observedwithout muscle substitution. Reinold et

    al70 report that adding a towel roll to the

    exercise consistently exhibited a tendency

    towards higher activity o the posterior

    rotator cuf muscles as well. An increase

    o 20% to 25% in EMG signal o the in-

    raspinatus and teres minor was noted

    when using the towel roll compared to

    no towel roll.

    What is not readily apparent is the

    strengthening the scapular retractors and

    maintaining a scapular retracted posture

    during shoulder exercises. The authors

    routinely instruct patients to emphasize

    an upright posture and a retracted posi-tion o the scapula during all shoulder

    and scapula strengthening exercises.

    Thus, the ull can exercise appears to

    be the most advantageous exercise while

    the empty can exercise is not commonly

    recommended. The prone ull can exer-

    cise warrants urther consideration be-

    cause the exercise results in greater EMG

    signal o the posterior deltoid than the

    middle deltoid, which may result in less

    superior sheer orce. The prone ull can

    exercise may also be beneficial because o

    scapular muscle recruitment.

    ?d\hWif_dWjkiWdZJ[h[iC_dehThe inraspinatus and teres minor com-

    prise the posterior cuf, which provides

    glenohumeral compression and resists

    superior and anterior humeral head

    translation by exerting an ineroposteri-

    or orce on the humeral head.74 The pos-

    terior cuf muscles provide glenohumeral

    ER, which unctionally helps clear the

    greater tuberosity rom under the cora-

    coacromial arch during overhead move-

    ments, thus minimizing subacromial

    impingement.

    Based on 3-D biomechanical shoulder

    models, the maximum predicted isomet-

    ric inraspinatus orce was 723 N or ER

    at 90 o abduction and 909 N or ER at

    0 o abduction.34 The maximum predict-

    ed teres minor orce was much less than

    or the inraspinatus during maximum

    ER at both 90 (111 N) and 0 abduction

    (159 N).34 The efectiveness o the muscles

    o the posterior rotator cuf to externallyrotate the arm depends on glenohumeral

    position. The superior, middle, and ine-

    rior heads o the inraspinatus have their

    largest ER moment arm (approximate-

    ly 2.2 cm) and generate their greatest

    torque at 0 abduction.65 As the abduc-

    tion angle increases, the moment arms o

    the inerior and middle heads stay rela-

    tively constant, while the moment arm o

    the superior head progressively decreases

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    journal o orthopaedic & sports physical therapy | volume 39 | number 2 | ebruary 2009 | 109

    significant role o the inraspinatus as

    a shoulder abductor in the scapular

    plane.34,50,65 From 3-D biomechanical

    shoulder models, predicted inraspina-

    tus orce during maximum isometricefort scapular plane abduction (90

    position) was 205 N, nearly twice the

    predicted orce rom the supraspinatus

    in this position.34 Liu et al50 reported

    that in scapular plane abduction with

    neutral rotation the inraspinatus has an

    abductor moment arm that was small at

    0 abduction, but increased to 1 cm at

    15 abduction, and remained airly con-

    stant throughout increasing abduction

    angles. Moreover, inraspinatus activity

    increases as resistance increases, peaking

    at 30 to 60 or any given resistance.1 As

    resistance increases, inraspinatus activ-

    ity increases to help generate a higher

    shoulder scapular abduction torque, and,

    at lower elevation angles, inraspinatus

    activity increases to resist superior hu-

    meral head translation due to the action

    o the deltoid.74

    In contrast to the inraspinatus, the

    teres minor generates a weak shoulder

    adductor torque due to its relatively

    lower attachments to the scapula and hu-

    merus.34,50,65 A 3-D biomechanical mod-

    el o the shoulder reveals that the teres

    minor does not generate scapular plane

    abduction torque when it contracts, but,

    rather, generates an adduction torque

    and 94 N o orce during maximum efort

    scapular plane adduction.34 In addition,

    Otis et al65 reported that the adductor

    moment arm o the teres minor was ap-

    proximately 0.2 cm at 45 o IR and ap-

    proximately 0.1 cm at 45 o ER. These

    data imply that the teres minor is a weak

    adductor o the humerus, regardless othe rotational position o the humerus.

    In addition, because o its posterior posi-

    tion at the shoulder, it also helps gener-

    ate a weak horizontal abduction torque.

    Thereore, although its activity is simi-

    lar to the inraspinatus during ER, it is

    hypothesized that the teres minor would

    not be as active as the inraspinatus dur-

    ing scapular abduction, abduction, and

    flexion movements, but would show ac-

    tivity similar to that o the inraspina-

    tus during horizontal abduction. This

    hypothesis is supported by EMG and

    magnetic resonance imaging data, which

    show that teres minor activity duringflexion, abduction, and scapular abduc-

    tion is drastically less than inraspinatus

    activity.1,3,5,54,77,79 Even though the teres

    minor generates an adduction torque, it

    is active during these diferent elevation-

    type movements, as it likely acts to en-

    hance joint stability by resisting superior

    humeral head translation and providing

    humeral head compression within the

    glenoid ossa.74 This is especially likely

    the case at lower shoulder abduction

    angles and when abduction and scapu-

    lar abduction movements are perormed

    against greater resistance.1 In contrast to

    the movements o shoulder abduction,

    scapular abduction, and flexion, teres mi-

    nor activity is much higher during prone

    horizontal abduction at 100 abduction

    with ER, exhibiting similar activity as the

    inraspinatus.5,54,70,77,79

    IkXiYWfkbWh_iThe subscapularis provides glenohumer-

    al compression, IR, and anterior stability

    o the shoulder. From 3-D biomechanical

    shoulder models, predicted subscapu-

    laris orce during maximum efort IR

    was 1725 N at 90 abduction and 1297

    N at 0 abduction.34 Its superior, middle,

    and inerior heads all have their larg-

    est IR moment arm (approximately 2.5

    cm) and torque generation at 0 abduc-

    tion.65 As the abduction angle increases,

    the moment arms o the inerior and

    middle heads stay relatively constant,

    while the moment arm o the superior

    head progressively decreases until it isabout 1.3 cm at 60 abduction.65 These

    data imply that the upper portion o the

    subscapularis muscle (innervated by the

    upper subscapularis nerve) may be a

    more efective internal rotator at lower

    abduction angles compared to higher ab-

    duction angles. However, there is no sig-

    nificant diference in upper subscapularis

    activity among IR exercises perormed at

    0, 45, or 90 abduction.17,39 Abduction

    angle does not appear to afect the ability

    o the lower subscapularis (innervated by

    the lower subscapularis nerve) to gener-

    ate IR torque.65 However, lower sub-

    scapularis muscle activity is afected byabduction angle, where some EMG data

    show significantly greater activity with

    IR at 0 abduction compared to IR at 90

    abduction,17 while EMG data o another

    study show greater activity with IR ex-

    ercise perormed at 90 compared to 0

    abduction.39 Perorming IR at 0 abduc-

    tion produces similar amounts o upper

    and lower subscapularis activity.17,28,39

    Although biomechanical data remain

    inconclusive as to which position to per-

    orm IR exercises (0 versus 90 abduc-

    tion), during IR at 0 abduction the action

    o the subscapularis is assisted by several

    large muscles, such as the pectoralis ma-

    jor, latissimus dorsi, and teres major.17

    Clinically, this may allow or compensa-

    tion o larger muscles during the exercise

    in the presence o subscapularis weak-

    ness. Decker et al17demonstrated that IR

    at 90 abduction produced less pectoralis

    major activity compared to 0 abduction.

    The authors findings revealed that pecto-

    ralis major and latissimus dorsi activity

    increased when perorming IR exercises

    in an adducted position or while mov-

    ing into an adducted position during the

    exercise. Thus, IR at 90 abduction may

    be perormed i attempting to strengthen

    the subscapularis while minimizing larg-

    er muscle group activity.

    The subscapularis is active in numer-

    ous shoulder exercises other than specific

    IR o the shoulder. Decker et al 17reported

    high subscapularis activity during the

    push-up with plus and dynamic-hug ex-

    ercises. These authors also described an-other exercise that consistently produced

    high levels o subscapularis activity, which

    they called the diagonal exercise (

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    [ CLINICAL COMMENTARY ]

    clock, depression, elevation, protraction,

    and retraction movements.17,33,44,63,75,79

    The subscapularis also generates

    an abduction torque during arm eleva-

    tion.50,65 From 3-D biomechanical shoul-

    der models, predicted subscapularis orce

    during maximum efort scapular plane

    abduction at 90 was 283 N, approxi-

    mately 2.5 times the predicted orce or

    the supraspinatus in this position.34 This

    was similar to that o the inraspinatus,

    highlighting the theoretical orce couple

    that the 2 muscles provide to center the

    humeral head within the glenoid ossa

    during abduction. Liu et al50 reported

    that in scapular plane abduction with

    neutral rotation the subscapularis had a

    peak abductor moment arm o 1 cm at 0

    abduction, which slowly decreased to 0

    cm at 60 abduction. Moreover, the ab-

    ductor moment arm o the subscapularisgenerally decreased as abduction was per-

    ormed with greater shoulder IR,50 such

    as perorming the empty can exercise. In

    contrast, the abductor moment arm o

    the subscapularis generally increased as

    abduction was perormed with greater

    shoulder ER, similar to perorming the

    ull can exercise.

    Otis et al65 reported that the superior,

    middle, and inerior heads o the sub-

    scapularis all have an abductor moment

    arm (greatest or the superior head and

    least or the inerior head) that varies as a

    unction o humeral rotation. The lengths

    o the moment arm or the 3 muscle heads

    are approximately 0.4 to 2.2 cm at 45 o

    ER, 0.4 to 1.4 cm in neutral rotation, and

    0.4 to 0.5 cm at 45 o IR. These data sug-

    gest that the subscapularis is most efec-

    tive as a scapular plane abductor with the

    shoulder in ER and least efective with

    the shoulder in IR. Thereore, the simul-

    taneous activation o the subscapularis

    and inraspinatus during arm elevation

    generates both an abductor moment and

    an ineriorly directed orce to the humer-

    al head to resist superior humeral head

    translation.74 In addition, a simultane-

    ous activation neutralizes the IR and ER

    torques these muscles generate, urther

    enhancing joint stability.

    DELTOID

    The deltoid plays an important

    role in shoulder biomechanics and

    during glenohumeral and scapu-

    lothoracic exercises. Extensive research

    has been conducted on deltoid activity

    during upper extremity weight-liting

    exercises, such as bench press, dumb-

    bell flys, military press, and push-

    ups.4,13,16,19,44,57,63,79,81,83

    The abductor moment arm is ap-

    proximately 0 cm or the anterior del-

    toid and 1.4 cm or the middle deltoidwhen the shoulder is in 0 abduction

    and neutral rotation in the scapular

    plane.50,65 The magnitude o these mo-

    ment arms progressively increases with

    shoulder abduction, such that, by 60

    o abduction, they are approximately

    1.5 to 2 cm or the anterior deltoid and

    2.7 to 3.2 cm or the middle deltoid.

    From 0 to 40o abduction the moment

    arms or the anterior and middle del-

    toids are less than the moment arms or

    the supraspinatus, subscapularis, and

    inraspinatus.50,65 These data suggest

    that the anterior and middle deltoid

    are not efective shoulder abductors at

    low abduction angles and the shoulder

    in neutral rotation, especially the ante-

    rior deltoid. This is in contrast to the

    supraspinatus and to a lesser extent the

    inraspinatus and subscapularis, which

    are more efective shoulder abductors

    at low abduction angles. These biome-

    chanical data are consistent with EMG

    data, in which anterior and middle del-

    toid activity generally peaks between

    60 to 90 o abduction in the scapular

    plane, while supraspinatus, inraspina-

    tus, and subscapularis activity generally

    peaks between 30 and 60 o shoulder

    abduction in the scapular plane.1

    The abductor moment arm or the

    anterior deltoid changes considerably

    with humeral rotation, increasing with

    ER and decreasing with IR.50 At 60 ER

    and 0 abduction, a position similar to

    the beginning o the ull can exercise, the

    anterior deltoid moment arm is 1.5 cm(compared to 0 cm in neutral rotation),

    which makes the anterior deltoid an e-

    ective abductor even at small abduction

    angles.50 By 60 abduction with ER, its

    moment arm increased to approximately

    2.5 cm (compared to approximately 1.5

    to 2 cm in neutral rotation).50 In con-

    trast, at 60 IR at 0 abduction, a po-

    sition similar to the beginning o the

    empty can exercise, its moment arm was

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    0 cm (the same as with neutral rotation),

    which suggests that in this position

    the anterior deltoid is not an efective

    abductor.50

    It has been reported that, given a peakisometric abduction torque o 25 Nm at

    0 abduction and neutral rotation, up to

    35% to 65% o this torque may be gener-

    ated by the middle deltoid, 30% by the

    subscapularis, 25% by the supraspinatus,

    10% by the inraspinatus, 2% by the an-

    terior deltoid, and 0% by the posterior

    deltoid.50 Interestingly, the rotator cuf

    provides a significant contribution to the

    abduction torque. The inefectiveness

    o the anterior and posterior deltoids to

    generate abduction torque with neutral

    rotation may appear surprising.50,65 How-

    ever, it is important to understand that

    the low abduction torque or the anterior

    deltoid does not mean that this muscle is

    only minimally active. In act, because the

    anterior deltoid has an abductor moment

    arm near 0 cm, the muscle could be very

    active and generate very high orce but

    very little torque (in 0 abduction this

    orce attempts to translate the humeral

    head superiorly).

    The aorementioned torque data are

    complemented and supported by muscle

    orce data rom Hughes and An.34 These

    authors reported predicted orces rom

    the deltoid and rotator cuf during maxi-

    mum efort abduction with the arm 90

    abducted and in neutral rotation. Poste-

    rior deltoid and teres minor orces were

    only 2 N and 0 N, respectively, which

    urther demonstrates the inefectiveness

    o these muscles as shoulder abductors.

    In contrast, middle deltoid orce was the

    highest at 434 N, which suggests a high

    contribution o this muscle during abduc-tion. The anterior deltoid generated the

    second highest orce o 323 N. This may

    appear surprising given the low abductor

    torque or this muscle reported above,

    but it should be re-emphasized that orce

    and torque are not the same, and that the

    shoulder was positioned at 90 abduction

    in the study by Hughes and An,34 in con-

    trast to 0 abduction in the study by Liu

    et al.50 As previously mentioned, the mo-

    ment arm o the anterior deltoid progres-

    sively increases as abduction increases,

    and it becomes a more efective abduc-

    tor. It is also important to remember

    that muscle orce is generated not only togenerate joint torque, but also to provide

    stabilization, such as joint compression.

    Also o interest is the 608-N orce that,

    collectively, the subscapularis (283 N),

    inraspinatus (205 N), and supraspinatus

    (117 N) generate. These larges orces are

    generated not only to abduct the shoul-

    der but also to compress and stabilize

    the joint, and neutralize the superiorly

    directed orce generated by the deltoid at

    lower abduction angles.

    It should also be noted that deltoid

    muscle orce in diferent shoulder posi-

    tions may also afect shoulder stability.

    All 3 heads o the deltoid generate a orce

    that increases shoulder stability at 60

    abduction in the scapular plane (helps to

    stabilize the humeral head in the glenoid

    ossa) but decreases shoulder stability at

    60 abduction in the rontal plane (tends

    to translate the humeral head anterior).48

    These data provide evidence or the use

    o scapular abduction exercises instead o

    abduction exercises or individuals with

    anterior instability.

    Thus, it appears that the 3 heads o

    the deltoid have diferent roles during

    upper extremity movements and, there-

    ore, diferent implications or exercise

    selection. The middle deltoid may have

    the most significant impact on superior

    humeral head migration, and exercises

    with high levels o middle deltoid activity

    (as well as anterior deltoid activity), such

    as the empty can exercise, should likely

    be minimized or most patients. Con-

    versely, high levels o posterior deltoidactivity may not be as disadvantageous

    as high levels o middle or anterior del-

    toid activity. It does not appear that the

    posterior deltoid has a significant role in

    providing abduction or superior humeral

    head migration. Thus, exercises such as

    the prone ull can, which generates high

    levels o rotator cuf and posterior deltoid

    activity, may be both sae and efective or

    rotator cuf strengthening.

    I97FKBEJ>EH79?9CKI9B;I

    T

    he primary muscles that con-

    trol scapular movements include the

    trapezius, serratus anterior, levatorscapulae, rhomboids, and pectoralis mi-

    nor. Appropriate scapular muscle strength

    and balance are important because the

    scapula and humerus move together in

    coordination during arm movement,

    reerred to as scapulohumeral rhythm.

    During humeral elevation, the scapula

    upwardly rotates in the rontal plane,

    rotating approximately 1 or every 2

    o humeral elevation until 120 humeral

    elevation, and thereater rotates approxi-

    mately 1 or every 1 humeral elevation

    until maximal arm elevation, achieving

    at least 45 to 55 o upward rotation.52,58

    During humeral elevation, in addition to

    scapular upward rotation, the scapula also

    normally tilts posteriorly approximately

    20 to 40 in the sagittal plane and exter-

    nally rotates approximately 15 to 35 in

    the transverse plane.52,58

    When the normal 3-D scapular move-

    ments are disrupted by abnormal scapular

    muscle-firing patterns, atigue, or injury,

    it has been hypothesized that the shoulder

    complex unctions less eciently, leading

    to injuries to the shoulder, including the

    glenohumeral joint.10,11,12,18,58,76,80,82 During

    arm elevation in the scapular plane, in-

    dividuals with subacromial impingement

    exhibit decreased scapular upward rota-

    tion, increased scapular IR (winging) and

    anterior tilt, and decreased subacromial

    space width, compared to those without

    subacromial impingement.24,51 Altered

    scapular muscle activity is commonly as-

    sociated with impingement syndrome.

    For example, upper and lower trapeziusactivity increased and serratus anterior

    activity decreased in individuals with im-

    pingement as compared to those without

    impingement.51 Thereore, it is important

    to include the scapulothoracic muscula-

    ture in the rehabilitation o patients with

    shoulder pathology.42

    I[hhWjki7dj[h_eh

    The serratus anterior works with the

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    pectoralis minor to protract the scapula

    and with the upper and lower trapezius

    to upwardly rotate the scapula. The ser-

    ratus anterior is an important muscle be-

    cause it contributes to all components o

    normal 3-D scapular movements during

    arm elevation, which includes upward

    rotation, posterior tilt, and external ro-

    tation.52,58 The serratus anterior is also

    important in athletics, such as during

    overhead throwing, to accelerate the

    scapula during the acceleration phase o

    throwing. The serratus anterior also helps

    stabilize the medial border and ineriorangle o the scapula, preventing scapular

    IR (winging) and anterior tilt.

    Several exercises elicit high serratus

    anterior activity, such as D1 and D2 di-

    agonal PNF pattern flexion, D2 diagonal

    PNF pattern extension, supine scapular

    protraction, supine upward scapular

    punch, military press, push-up plus, gle-

    nohumeral IR and ER at 90 abduction,

    and shoulder flexion, abduction, and

    scaption with ER above 120.16,20,32,62,63

    Serratus anterior activity tends to increase

    in a somewhat linear ashion with arm el-

    evation.2,20,29,52,62 However, increasing arm

    elevation increases subacromial impinge-

    ment risk,15,71 and arm elevation at lower

    abduction angles also generates relatively

    high serratus anterior activity.20

    It is interesting that perorming

    shoulder IR and ER at 90 o abduction

    generates relatively high serratus ante-

    rior activity, because these exercises are

    usually thought to primarily work rotator

    cuf muscles.20,63 However, during IR and

    ER at 90 abduction the serratus ante-

    rior helps stabilize the scapula. It should

    be noted that the rotator cuf muscles

    also act to move the scapula (where they

    originate) in addition to the humerus.

    For example, the orce exerted by the su-praspinatus at the supraspinous ossa has

    the ability to downwardly rotate the scap-

    ula i this orce is not counterbalanced by

    the scapulothoracic musculature.

    Not surprising is high serratus ante-

    rior activity generated during a push-up

    exercise. When perorming the stan-

    dard push-up, push-up on knees, and

    wall push-up, serratus anterior activity

    is greater when ull scapular protrac-

    tion occurs ater the elbows ully extend

    (push-up plus).53 Moreover, serratus

    anterior activity was lowest in the wall

    push-up plus, exhibited moderate activi-

    ty during the push-up plus on knees, and

    relatively high activity during the stan-

    dard push-up plus.16,53 Compared to the

    standard push-up, perorming a push-

    up plus with the eet elevated produced

    significantly greater serratus anterior

    activity.47 These findings demonstrate

    that serratus anterior activity increases

    as the positional (gravitational) chal-

    lenge increases.

    Decker et al16 compared several com-

    mon exercises designed to recruit the ser-

    ratus anterior. The authors identified that

    the 3 exercises that produced the great-

    est serratus anterior EMG signal were the

    push-up with a plus, dynamic hug (

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    tion and during a diagonal exercise that

    incorporated protraction with shoulder

    flexion, horizontal adduction, and exter-

    nal rotation. It appears that the punch ex-

    ercise can be enhanced by starting at 0abduction and extending the elbow, while

    elevating and protracting the shoulder

    (

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    reported during D2 diagonal PNF pat-

    tern flexion and extension, standing

    shoulder ER at 0 and 90 abduction,

    standing shoulder IR at 90 abduction,

    standing shoulder extension rom 90

    to 0, prone shoulder horizontal abduc-

    tion at 90 abduction with IR, scapular

    abduction, abduction, and shoulder flex-

    ion above 120 with ER, prone rowing,

    and standing high, mid, and low scapu-

    lar rows.62,63 Relatively high rhomboids

    and levator scapulae activity has been

    reported with scapular abduction above

    120 with ER, prone horizontal abduc-tion at 90 abduction with ER and IR,

    prone rowing, and prone extension at

    90 flexion.62 Thereore, the prone ex-

    tension exercise may be perormed in

    addition to many o the previously men-

    tioned exercises or other scapulotho-

    racic muscles. Other specific exercises

    to activate the rhomboids and levator

    scapulae muscles are not oten neces-

    sary to perorm.

    H;9ECC;D:7J?EDI

    T

    he preceding review can be used

    to identiy appropriate rehabilitation

    exercises or specific muscles. Basedon the reported studies and the collective

    experience o the authors, we recommend

    that exercises should be selected based on

    the appropriate anatomical, biomechani-

    cal, and clinical implications. We have

    identified a set o exercises that the cur-

    rent authors use clinically or rehabilita-

    tion and injury prevention (TABLE). These

    exercises have been selected based on the

    results o the numerous studies previous-

    ly cited and take into consideration these

    implications or each exercise described.

    Furthermore, the authors encourage the

    clinician to careully consider emphasiz-

    ing posture and scapular retraction dur-

    ing the perormance o glenohumeral and

    scapulothoracic exercises.

    A common recommendation in reha-

    bilitation is to limit the amount o weight

    used during glenohumeral and scapu-

    lothoracic exercises to assure that the ap-

    propriate muscles are being utilized and

    not larger compensatory muscles. Two

    recent studies have analyzed this theory

    and appear to prove the recommenda-

    tion inaccurate and not necessary. Alpert

    et al7studied the rotator cuf and deltoid

    muscles during scapular plane elevation

    and noted that EMG signal amplitude

    o the smaller rotator cuf muscles and

    larger deltoid muscles increased linearly

    in relation to the amount o weight used.

    This finding is consistent with that o

    Dark et al,14 who showed similar results

    or the rotator cuf, deltoid, pectoralis,

    and latissimus dorsi during ER and IR

    at 0 abduction. Thus, it appears thatlarger muscle groups do not overpower

    smaller groups, such as the rotator cuf.

    Weight selection should be based on the

    individual goals and perormance o each

    patient. It does not appear necessary to

    limit the amount o weight perormed

    during these rotator cuf exercises.

    As our understanding o the anatomi-

    cal and biomechanical implications asso-

    ciated with exercise selection continues

    to grow, we are seeing advances in exer-

    cise selection and the integration o the

    whole-body kinetic-chain approach to

    strengthening and rehabilitating injuries.

    This may involve strengthening multiplejoints simultaneously and during move-

    ment patterns that mimic athletic and

    unctional daily activities o living. The

    authors oten employ these techniques

    when our patients improve in strength

    yet continue to have symptoms during

    activities. In addition, we oten attempt

    to urther challenge our patients by per-

    orming many o the recommended exer-

    cise on various unstable suraces (such as

    oam or physioballs), with altered bases

    o support (such as sitting, standing, or

    single-leg balancing), in an attempt to

    recruit whole-body muscle patterns that

    interact together to perorm active range

    o motion while stabilizing other areas o

    the body. We believe that these concepts

    are important to consider in addition to

    straight-plane, isolated movements o

    specific muscle groups, and that strength,

    posture, balance, and neuromuscular

    control are all vital components to any

    injury prevention o rehabilitation pro-

    gram. Future research on the validity o

    these techniques is needed to justiy their

    use. We believe that this is the next step

    in the evolution o research on the clini-

    cal and biomechanical implications o

    exercise selection or the glenohumeral

    and scapulothoracic musculature.

    9ED9BKI?ED

    Athorough understanding o

    the biomechanical actors as-

    sociated with normal shoulder

    movement, as well as during commonlyperormed exercises, is necessary to

    saely and efectively design appropriate

    programs. We have reviewed the normal

    biomechanics o the glenohumeral and

    scapulothoracic muscles during unc-

    tional activities, common exercises, and

    in the presence o pathology. These find-

    ings can be used by the clinician to design

    appropriate rehabilitation and injury

    prevention programs. T

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    TABLERecommended Exercises or Glenohumeral and Scapulothoracic Muscles

    Based on Anatomical, Biomechanical, and Clinical Implications

    Abbreviations: EMG, electromyography; ER, external rotation; IR, internal rotation.

    CkiYb[ ;n[hY_i[ 7dWjec_YWb?cfb_YWj_edi 8_ec[Y^Wd_YWb?cfb_YWj_edi 9b_d_YWb?cfb_YWj_edi

    Supraspinatus 1. Full can 1. Enhances scapular position andsubacromial space

    1. Decreased deltoid involvementcompared to empty can

    1. Minimizes chance o superior humeral head migration bydeltoid overpowering supraspinatus

    2. Prone ull can 2. Enhances scapular position andsubacromial space

    2. High posterior deltoid activitywith similar supraspinatus activity

    2. High supraspinatus activity and also good exercise orlower trapezius

    Inraspinatusand teresminor

    1. Side-lying ER 1. Position o shoulder stability,minimal capsular strain

    1. Increased moment arm omuscle at 0 abduction.Greatest EMG activity

    1. Most efective exercise in recruiting inraspinatus activity.Good when cautious with static stability

    2. Prone ER at 90abduction

    2. Challenging position or stability,higher capsular strain

    2. High EMG activity 2. Strengthens in a challenging position or shoulder stability.Also good exercise or lower trapezius

    3. ER with towel roll 3. Allows or proper orm withoutcompensation

    3. Increased EMG activity withaddition o towel, also incorpo-rates adductors

    3. Enhances muscle recruitment and synergy with adductors

    Subscapularis 1. IR at 0 abduction 1. Position o shoulder stability 1. Similar subscapularis activitybetween 0 and 90 abduction

    1. Efective exercise, good when cautious with static stability

    2. IR at 90 abduction 2. Position o shoulder instability 2. Enhances scapular position andsubacromial space. Lesspectoralis activity

    2. Strengthens in a challenging position or shoulder stability

    3. IR diagonal exercise 3. Replicates more unctional activity 3. High EMG activity 3. Efective strengthening in a unctional movement pattern

    Serratus anterior 1. Push-up with plus 1. Easy position to produceresistance against protraction

    1. High EMG activity 1. Efective exercise to provide resistance against protraction,also good exercise or subscapularis

    2. Dynamic hug 2. Perormed below 90 abduction 2. High EMG activity 2. Easily perorm in patients with diculty elevating arms orperorming push-up. Also good exercise or subscapularis

    3. Serratus punch 120 3. Combines protraction withupward rotation

    3. High EMG activity 3. Good dynamic activity to combine upward rotation andprotraction unction

    Lower trapezius 1. Prone ull can 1. Can properly align exercise withmuscle fibers

    1. High EMG activity 1. Efective exercise, also good exercise or supraspinatus

    2. Prone ER at 90

    abduction

    2. Prone exercise below 90

    abduction

    2. High EMG activity 2. Efective exercise, also good exercise or inraspinatus and

    teres minor3. Prone horizontal

    abduction at 90abduction with ER

    3. Prone exercise below 90abduction

    3. Good ratio o lower to uppertrapezius activity

    3. Efective exercise, also good exercise or middle trapezius

    4. Bilateral ER 4. Scapular control without armelevation

    4. Good ratio o lower to uppertrapezius activity

    4. Efective exercise, also good or inraspinatus and teres minor

    Middle trapezius 1. Prone row 1. Prone exercise below 90abduction

    1. High EMG activity 1. Efective exercise, good ratios o upper, middle, and lowertrapezius activity

    2. Prone horizontalabduction at 90abduction with ER

    2. Prone exercise below 90abduction

    2. High EMG activity 2. Efective exercise, also good exercise or lower trapezius

    Upper trapezius 1. Shrug 1. Scapular control without armelevation

    1. High EMG activity 1. Efective exercise

    2. Prone row 2. Prone exercise below 90

    abduction

    2. High EMG activity 2. Good ratios o upper, middle, and lower trapezius activity

    3. Prone horizontalabduction at 90abduction with ER

    3. Prone exercise below 90abduction

    3. High EMG activity 3. Efective exercise, also good exercise or lower trapezius

    Rhomboids andlevator scapulae

    1. Prone row 1. Prone exercise below 90abduction

    1. High EMG activity 1. Efective exercise, good ratios o upper, middle, and lowertrapezius activity

    2. Prone horizontalabduction at 90abduction with ER

    2. Prone exercise below 90abduction

    2. High EMG activity 2. Efective exercise, also good or lower and middle trapezius

    3. Prone extension with ER 3. Prone exercise below 90 abduction 3. High EMG activity 3. Efective exercise, unique movement to enhance scapular control

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    H;

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