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We searched on the websites of Web of Science and Pubmed using the terms: "Scapular Humeral Rhythm", "Scapula Dyskinesia", "Scapula Position", "Scapula Stabilization", "Shoulder Movements", "Codman" and "Glenohumeral Motion".
Definition / Description
Scapulohumeral rhythm (also referred to as glenohumeral rhythm) is the kinematic interaction between the scapula and the humerus, first published by Codman in the 1930s. 
This interaction is important for the optimal function of the shoulder.  When there is a change ment of the normal position of the scapula(describe) relative to the humerus, can this can cause a disfunction of the scapulohumeral rhythm. The change ment of the normal position is also called scapular dyskinesia. Various studies of the mechanism of the shoulder joint have attempted to describe the global motion capacity of the shoulder refer to that description, can you evaluate the shoulder to see if the function is correct? and explain the complex interactions between components involved in placing the hand in space. 
Clinical Relevant Anatomy
The interplay of 4 articulations (Sternoclavicular Joint, Acromioclavicular Joint, Scapulothoracic Joint and Glenohumeral Joint) of the shoulder complex, results in an coordinated movement pattern of the arm elevation. The involved movements at each joint are continuous, although occurring at various rates and at different phases of arm elevation. The movement of the scapula can be described by rotations in relation to the thorax. The scapula moves around a dorso-ventral axis, resulting in a rotation in the frontal plane. In this movement the glenoid cavity is turned cranially (upward rotation) or caudally (downward rotation). In the sagittal plane, around a latero-lateral axis the scapula rotates posteriorly (posterior tilting) or anteriorly (anterior tilting). External and internal rotation occurs around a cephalo-caudal (longitudinal) axis. The external rotation brings the glenoid cavity more into the frontal plane, whereas the internal rotation turns the glenoid cavity more to the sagittal plane. 
When we perform flexion, the glenohumeral (GH) joint contributes 100°-120°. The scapula on the thorax contributes to elevation (flexion and abduction) of the humerus by upwardly rotating the glenoid fossa 50° to 60° from its resting position. If the humerus were fixed to the fossa, this alone would result in up to 60° of elevation of the humerus. The humerus, of course, is not fixed but can move independently on the glenoid fossa.
Inman et al. reported an inconsistent amount and type of scapular motion in relation to GH-motion during the initial 60°.  In this early phase (0-60°), motion occurs primarily at the GH joint, although stressing the arm may increase the scapular contribution.  During abduction of the humerus in the plane of the scapula, an average of 43° of lateral rotation from the resting position has been reported, with peak lateral rotation generally occurring between 90° and 120° of humeral elevation. It must also be recognized, however, that elevation of the arm is often accompanied not only by elevation of the humerus but also by lateral rotation of the humerus in relation to the scapula. 
When we perform abduction, the GH-joint contributes 90-120°. The combination of scapular and humeral movement result in a maximum range of elevation of 150-180°.   Also by abduction Inman et al. reported an inconsistent amount and type of scapular motion in relation to GH-motion this time during the initial 30°.  In this early phase, motion occurs primarily at the GH joint, although stressing the arm may increase the scapular contribution. 
Scapulohumeral rhythm or ratio is significantly greater (less scapular motion and more humeral motion) in the sagittal plane than other planes. Consistent with the findings, the dominant side demonstrated significantly higher values for SH rhythm than the non-dominant side but only in the coronal and scapular planes but not in the sagittal plane.  By healthy male is a significant difference by hand dominance only in scapular upward rotation during scapular plane arm elevation.
The scapulohumeral rhythm is therefore defined as the ratio of the glenohumeral movement to the scapulothoracic movement during arm elevation. This is most often calculated by dividing the total amount of shoulder elevation (humerothoracic) by the scapular upward rotation (scapulothoracic). 
In the literature Scapulohumeral rhythm is descibed like a ratio: humeral elevation:scapulothoracal rotation. The overall ratio of 2:1during arm elevation is commonly used. According to the 2-to-1 ratio frame-work, flexion or abduction of 90° in relation to the thorax would be accomplished through approximately 60° of GH and 30° of ST motion. In another study of Scapulohumeral rhythm between children and adults, the mean ratio for the scapular plane was 2.4:1 for adults, 1.3:1 for children. 
If we compare the scapulohumeral rhythm by children with adults, we see that children showed a higher scapulohumeral rhythm during lowering of the arm than adults.  Also during scapular plane rotation from 25° to 125°, children showed greater upward rotation than adults. 
Epidemiology / Etiology
It has been reported that scapular dyskinesis occurs in 68 - 100 % of patients with shoulder injuries (including glenohumeral instability, rotator cuff abnormalities, and labral tears.  Other studies showed that scapular upward rotation is significantly increased in patients with full-thickness rotator cuff tears compared with controls in both sagittal and scapular plane elevation. Also, an increased scapular component is generally thought to contribute to the scapulohumeral rhythm ratio in frozen or stiff shoulders. 
Given the role of the scapula in shoulder function, the ability to monitor the coordinated motion of the scapula and humerus (scapulohumeral rhythm) may have clinical implications when dealing with overhead athletes and patients with shoulder pathologies. 
Sports participation results in slight differences in side-to-side motion and in scapular resting position in overhead athletes.   Overhead athletes have some asymmetry in scapular upward rotation and scapulohumeral rhythm ratio between dominant and non-dominant shoulder. It should not be considered automatically as a pathological sign but rather an adaptation to sports practice and extensive use of upper limb. 
People with higher BMI have scapula kinematic patterns different from people with lower BMI. They have increased scapula upward rotation during arm elevation. 
Characteristics / Clinical Presentation
Scapulohumeral rhythm is a common metric for assessing muscle function and shoulder joint motion. There is a three-dimensional scapular kinematic pattern during normal arm elevation that include upward rotation, posterior tilting and varying internal/external rotation dependent on the plane and angle of elevation.   When there is a changement of the normal position of the scapula related to the humerus, the scapulohumeral rhythm is disturbed.
There isn’t really a differential diagnosis for scapulohumeral rhythm disorders. But there are multiple causes for scapular dyskinesia and scapulohumeral rhythm disorders.  Causative factors can be grouped into:
- Bony causes include thoracic kyphosis or clavicula fracture.
- Joint causes include high grade AC instability, AC arthrosis and instability and GH joint internal derangement.
- Neurological causes include Cervical Radiculopathy, long thoracic or spinal accessorynerve palsy.
- Inflexibility causes, for example: 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 GH internal rotation deficit (GIRD), which creates a ‘wind-up’ of the scapula on the thorax with reduced humeral internal rotation and horizontal abduction.
- Muscular causes: Serratus anterior activation and strength is decreased in patients with impingement and shoulder pain, contributing to the loss of posterior tilt and upward rotation causing dyskinesis.   In addition, the upper trapezius/lower trapezius force couple may be altered, with delayed onset of activation in the lower trapezius, which alters scapular upward rotation and posterior tilt. Altered scapular motion or position both decrease linear measures of the subacromial space  , increase impingement symptoms, decrease rotator cuff strength , increase strain on the anterior GH ligaments 
Alterations in scapular position and control afforded by the scapula stabilizing muscles are believed to disrupt stability and function of the glenohumeral joint   , thereby contributing to shoulder impingement, rotator cuff pathology and shoulder instability. 
Inman, Saunders and Abbott were the first to measure scapulohumeral rhythm using radiography and suggested what became the widely accepted 2:1 ratio between glenohumeral elevation and scapulothoracic (ST) upward rotation (SUR). 
The Simple Shoulder Test (SST) is an internationally used patient-reported outcome for clinical practice and research purposes. It was developed for measuring functional limitations of the affected shoulder in patients with shoulder dysfunction and contains 12 questions (yes/no). It is a reliable and valid instrument for evaluating functional limitations in patients with shoulder complaints. 
Other frequently used questionnaires are: the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire, the Shoulder Pain and Disability Index (SPADI) and the American Shoulder and Elbow Surgeons (ASES) score. These questionnaires have been shown acceptable for clinical use.  These questionnaires are not specific for scapulohumeral rhythm disorders, but may help in the diagnostic proces.
Observation and examination of the scapulohumeal rhythm is commonly performed by physical therapists during postural and shoulder examinations. The notion of a proper "rhythm" is routinely used to describe the quality of movement at the shoulder complex.
Clinical measures (inclinometer, tape measure) are only capable of measuring scapular kinematics 2-dimensionally.
The inclinometer is capable of measuring angles (in degrees) from a horizontal reference to assess static positions of scapular upward rotation, this upward rotation can easily be used by clinicians when evaluating the scapular motion. Different authors have demonstrated that these clinical assessments give valid and accurate information regarding scapular kinematics.   
Linear assessment using tape measures can be used to examine possible asymmetries and patterns of abnormal motion between the pathological and healthy scapula. This examination is based on simple bilateral visual observation of scapular position.  Although this method is a subjective approach, research gave evidence that it is a qualitative method. 
Quantitative measurement of scapular positioning can also be achieved with LSST (lateral scapular slide test). This test evaluates the scapular symmetry while varying loads are placed on the supporting musculature. Three positions of the upper extremities are proposed:
- Position 1, the subject's arm is relaxed at the side (0° of humeral elevation);
- Position 2, the subject places his or her hand on the lateral iliac crest;
- Position 3 corresponds to an internally rotated and abducted arm to 90°.
Two measurements are performed using a tape in each position (between the inferior angle of the scapula and the closest spinous process) in order to allow calculation of an average value. 
A 1.5-cm asymmetry in any of the positions is established as a threshold for an abnormal pattern.
Intratester reliability of the Kibler LSST method ranged from good to high, although the intertester reliability was poor.  Nijs et al. observed coefficients of >0.70 (interobserver reliability in intraclass correlation coefficients). The clinical importance of the tests' outcomes, however, is questionable.  
Another test is the SDT (scapular dyskinesis test). The SDT is a visually based test for scapular dyskinesis that involves a patient performing weighted shoulder flexion and abduction movements while scapular motion is visually observed. This test consists of characterising scapular dyskinesis as absent or present and each side is rated separately. Dyskinesis is defined as the presence of either winging (prominence of any portion of the medial border or inferior angle away from the thorax) or dysrhythmia (premature, or excessive, or stuttering motion during elevation and lowering).  Good inter-rater reliability of this test (75–82% agreement; weighted κ=0.48–0.61) was achieved. 
Optimal rehabilitation of scapulohumeral rhythm disorders 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. 
Physical therapy management
It is essential to make a diagnosis about the cause of the scapulohumeral rhythm disfunction before starting physical therapy. For example ‘Winged scapula’ of the scapula may be caused by a paresis of the m. Serratus Anterior or by a disfunction of the m. Trapezius.
Both passive and active movement disturbances can cause a scapulohumeral rhythm disfunction. Causes may be: shortening of muscles like m. Pectoralis Minor, m. Latissimus Dorsi and m. Levator Scapulae, shortening of the posterior joint capsule and/or lack of coordination between essential muscles like the m. Serratus Anterior, m. Trapezius and Rotatorcuff muscles (LoE: 3B). 
It may be clear that every therapy should be individualized.
Shortening of muscles or connective tissue must be done by stretching and/or active and passive mobilizations. It’s important that the patient gets a home exercise program to continue stretching and mobilizations (LoE: 5).  Middle thoracic manipulations in seated position have no influence on the scapulohumeral rhythm and scapular kinematics during arm flexion and thus should be avoided (LoE: 1B). 
Training the coordination between muscles should be done in two phases. Phase one will include the ‘setting’ of the muscles. In this phase the patient will learn how to subtle contract his muscles. Tactile feedback or myofeedback may be necessary during this phase. Practicing at home is important to train the duration of muscle contraction and train in other positions so that contraction is possible in every posture of daily life. In phase two the contraction should be automated. This can be trained with stabilization exercises. Exercises on the back should be avoided because muscles should stabilize the scapula instead of the ground. The stabilization exercises should be static and dynamic (LoE:3B).  Examples of exercises are: push up plus, press-up, low-rowing, horizontal abduction, serratus punch and dynamic hug (LoE:5). 
Muscles should be trained in functional patterns (sport or activity specific patterns) instead of isolated patterns because it will cause maximal scapular muscle activations (LoE: 4). 
Most abnormalities will occur in the eccentric phase of movements or with a lot of repetitions (fatigue). So it’s important not to forget to train the eccentric phase and endurance of the muscles (LoE:2C). 
With shoulder patients you should always be aware of the influence on the spine. Some patients could have a high degree of Thoracic Hyperkyphosis. Which can be treated with active and passive mobilizations of the thoracic spine (LoE:1B). 
WB Kibler et al., Clinical implications of scapular dyskinesis in shoulder injury: the 2013 consensus statement from the ‘scapular summit’, British Journal of Sports Medicine, 2013 Sep;47(14):877-85. Level of Evidence: 1A. 
Looking at the importance of scapulohumeral rhythm disfunctions we can conclude that every scapulohumeral rhythm disfunction with complaints should get attention from the physiotherapist. Because this disfunction can have so many underlaying causitive factors it is a challenge for every therapist.
- ↑ Codman EA: The Shoulder,Boston: G.Miller & Company,1934
- ↑ 2.0 2.1 Kibler WB. The role of the scapula in athletic shoulder function. Am J Sports Med 1998;26:325-337 Level of Evidence: 3B
- ↑ Cathcart CW: Movements of the shouLder girdle involved in those of the arm on the trunk. J Anat Physiol 1884; 18:209-218.
- ↑ Cleland J: A lecture on the shoulder girdle and its movements. Lancet 1881;1:11-12.
- ↑ 5.0 5.1 Struyf, F., Scapular positioning and movement in unimpaired shoulders, shoulder impingement syndrome, and glenohumeral instability, Scandinavian Journal of Medicine and Science in sports, jrg20, nr3, 2011, p352. Level of Evidence: 4.
- ↑ 6.0 6.1 McClure P: Direct 3-dimensional measurement of scapular kinematics during dynamic movements in vivo.J Shoulder Elbow Surg 2001;10:269–277.
- ↑ 7.0 7.1 Inman B, Saunders J, Abbott L: Observations of function of the shoulder joint. J Bone Joint Surg Br 2004; 26:1. Level of Evidence: 4.
- ↑ 8.0 8.1 Lockhart RD. Movements of the Normal Shoulder Joint and of a case with Trapezius Paralysis studied by Radiogram and Experiment in the Living. J Anat 1930; 64: 288-302.
- ↑ McQuade K, Smidt G: Dynamic scapulohumeral rhythm: The effects of external resistance during elevation of the arm in the scapular plane. J Orthop Sports Phys Ther 1998; 27:125–133.
- ↑ Rundquist P, Anderson DD, Guanche CA, et al. Shoulder kinematics in subjects with frozen shoulder. Arch Phys Med Rehabil 2003; 84:1473–1479. Level of Evidence: 4.
- ↑ Barnes CJ, Van Steyn SJ, Fischer RA: The effects of age, sex, and shoulder dominance on range of motion of the shoulder. J Shoulder Elbow Surg 2001; 10:242– 246. Level of Evidence:4.
- ↑ Crosbie, J., Scapulohumeral rhythm and associated spinal motion, Clinical Biomechanics, v23, nr.2, 2008, p184-192. Level of Evidence: 4.
- ↑ Matsuki, K., In vivo 3-dimensional analysis of scapular kinematics: comparison of dominant and nondominant shoulders, v19,nr2, 2010, p209. Level of Evidence: 4.
- ↑ 14.0 14.1 Dayanidhi, S., Scapular kinematics during humeral elevation in adults and children, Clinical Biomechanics,n20, 2005, p600-606. Level of Evidence: 4.
- ↑ Fernanda, A.P., Differences in scapular kinematics and scapulohumeral rhythm during elevation and lowering of the arm between typical children and healthy adults, Journal of Electrimyography and Kinesiology, jrg.24, nr.1, 2014, blz.78. Level of Evidence: 4.
- ↑ Tsun-Shun Huang et al. Comprehensive classification test of scapular dyskinesis: A reliability study. Manual Therapy 2015, 20(3): 427-432. Level of Evidence: 4.
- ↑ 17.0 17.1 Hosseinimehr SH et al. The comparison of scapular upward rotation and scapulohumeral rhythm between dominant and non-dominant shoulder in male overhead athletes and non-athletes. Manual Therapy, 2015 March. Level of Evidence: 3B.
- ↑ JS Scibek et al. Assessment of scapulohumeral rhythm for scapular plane shoulder elevation using a modified digital inclinometer. World Journal Of Orthopedics. 2012 Jun, 3(6): 87–94. Level of Evidence: 3B.
- ↑ Laudner KG et al. Scapular dysfunction in throwers with pathologic internal impingement. J Orthop Sports Phys Ther. 2006 Jul;36(7):485-94. Level of Evidence: 3B.
- ↑ Sakiko Oyama et al. Asymmetric Resting Scapular Posture in Healthy Overhead Athletes. Journal of Athletic Training. 2008 Nov-Dec; 43(6): 565–570. Level of Evidence: 3B.
- ↑ Miti Gupta et al. Scapula Kinematics Differ by Body Mass Index. Journal of Applied Biomechanics, 2013, 29: 380-385. Level of Evidence: 3B.
- ↑ Walker et al. Scapulohumeral Rhythm in Shoulders with Reverse Shoulder Arthroplasty. Journal of Shoulder and Elbow Surgery April 2015, 24(4). Level of Evidence: 4.
- ↑ PM. Ludewig et al. Motion of the Shoulder Complex During Multiplanar Humeral Elevation. Journal of Bone and Joint Surgery Am. 2009 Feb; 91(2): 378–389. Level of Evidence: 4.
- ↑ Kibler WB et al., Scapular dyskinesis and its relation to shoulder injury, J Am Acad Orthop Surg, 2012 Jun;20(6):364-72. Level of Evidence: 3A.
- ↑ Borstad JD et al., The effect of long versus short pectoralis minor resting length on scapular kinematics in healthy individuals, J Orthop Sports Phys Ther 2005;35:227–38. Level of Evidence: 3B.
- ↑ McQuade KJ et al., Effects of local muscle fatigue on three-dimensional scapulohumeral rhythm, Clin Biomech, 1995 Apr;10(3):144-148. Level of Evidence: 4.
- ↑ 27.0 27.1 Cools AM et al., Rehabilitation of scapular muscle balance, Am J Sports Med 2007;35:1744–51. Level of Evidence: 4.
- ↑ Seitz AL et al., Effects of scapular dyskinesis and scapular assistance test on subacromial space during static arm elevation. J Shoulder Elbow Surg 2012;21:631–40. Level of Evidence: 3B.
- ↑ Atalar H et al., Restricted scapular mobility during arm abduction: implications for impingement syndrome. Acta Orthopaedica Belgica 2009;75:19–24. Level of Evidence: 3B.
- ↑ Smith J et al., Effect of scapular protraction and retraction on isometric shoulder elevation strength. Arch Phys Med Rehabil 2002;83:367–70. Level of evidence: 3B.
- ↑ Weiser WM et al., Effects of simulated scapular protraction on anterior glenohumeral stability. Am J Sports Med 1999;27:801–5. and increase the risk of internal impingement. Level of Evidence: 4.
- ↑ Itoi E. Scapular inclination and inferior stability of the shoulder. J Shoulder Elbow Surg 1992;1:131-139. Level of Evidence: 5.
- ↑ Weiser WM, Lee TQ, McMaster WC, McMahon PJ. Effects of simulated scapular protraction on anterior glenohumeral stability. Am J Sports Med 1999; 27: 801-805. Level of Evidence: 5.
- ↑ 34.0 34.1 34.2 Ludewig PM, Reynolds JF. The association of scapular kinematics and glenohumeral joint pathologies. J Orthop Sports Phys Ther 2009;39: 90-104. Level of Evidence: 5.
- ↑ Inman VT, Saunders JB, Abbott LC. Observations of the function of the shoulder joint. 1944. Clin Orthop Relat Res 1996; 330: 3-12.
- ↑ Poppen NK, Walker PS. Normal and abnormal motion of the shoulder. J Bone Joint Surg Am 1976;58: 195-201. Level of Evidence: 4.
- ↑ Bagg SD, Forrest WJ. A biomechanical analysis of scapular rotation during arm abduction in the scapular plane. Am J Phys Med Rehabil 1988; 67: 238-245. Level of Evidence:4.
- ↑ Doody SG, Freedman L, Waterland JC. Shoulder movements during abduction in the scapular plane. Arch Phys Med Rehabil 1970; 51: 595-604.
- ↑ Doody SG, Waterland JC, Freedman L. Scapulo-humeral goniometer. Arch Phys Med Rehabil 1970; 51:711-713.
- ↑ Johnson MP, McClure PW, Karduna AR. New method to assess scapular upward rotation in subjects with shoulder pathology. J Orthop Sports Phys Ther 2001;31: 81-89. Level of Evidence: 3B.
- ↑ An KN, Browne AO, Korinek S, Tanaka S, Morrey BF. Three-dimensional kinematics of glenohumeral elevation. J Orthop Res 1991; 9: 143-149. Level of Evidence: 4.
- ↑ Johnson G, Stuart P, Mitchell S. A method for the measurement of three-dimensional scapular movement. Clin Biomech 1993; 8: 269-273. Level of Evidence: 4.
- ↑ Meskers CG, Fraterman H, van der Helm FC, Vermeulen HM, Rozing PM. Calibration of the “Flock of Birds” elec-tromagnetic tracking device and its application in shoulder motion studies. J Biomech 1999; 32: 629-633have been used to gain a better appreciation of shoulder kinematics.
- ↑ DA van Kampen et al., Validation of the Dutch version of the Simple Shoulder Test, J Shoulder Elbow Surg. 2012 Jun;21(6):808-14. Level of Evidence: 4.
- ↑ JS Roy et al., Measuring shoulder function: a systematic review of four questionnaires, Arthritis Rheum. 2009 May 15;61(5):623-32. Level of Evidence: 2A.
- ↑ McQuade KJ,Smidt GI. Dynamic Scapulohumeral Rhythm: The Effects of External Resistance During Elevation of the Arm in the Scapular Plane. J Orthop Sports Phys Ther 1998; 27(2): 125. Level of Evidence: 4.
- ↑ 47.0 47.1 47.2 Forthomme B et al., Scapular positioning in athlete's shoulder: particularities, clinical measurements and implications, Sports Med.;38(5):369-86, 2008. Level of Evidence: 2A.
- ↑ 48.0 48.1 Kibler WB, McMullen J. Scapular dyskinesis and its relation to shoulder pain. J Am Acad Orthop Surg 2003; 11: 142-51. Level of Evidence: 3A.
- ↑ Johnson MP, McClure PW, Karduna AR. New method to assess scapular upward rotation in subjects with shoulder pathology. J Orthop Sports Phys Ther 2001; 31: 81-9. Level of Evidence: 1B.
- ↑ 50.0 50.1 Nijs J, Roussel N, Vermeulen K, et al. Scapular positioning in patients with shoulder pain: a study examining the reliability and clinical importance of 3 clinical tests. Arch Phys Med Rehabil 2005; 86: 1349-55. Level of Evidence: 1B.
- ↑ Kibler WB et al., Qualitative clinical evaluation of scapular dysfunction: a reliability study, J Shoulder Elbow Surg, 2002, 11: 550-6. Level of Evidence: 4.
- ↑ Gibson MH et al. A reliability study of measurement techniques to determine static scapular position. J Orthop Sports Phys Ther 1995; 21: 100-6. Level of Evidence: 3B.
- ↑ McClure PW et al., A clinical method for identifying scapular dyskinesis: part 1: reliability. J Athl Train 2009;44:160–4. Level of Evidence: 3B.
- ↑ Tate AR et al., A clinical method for identifying scapular dyskinesis: part 2: Validity. J Athl Train 2009;44:165–73. Level of Evidence: 1B.
- ↑ Ludewig PM, Cook TM, Alterations in shoulder kinematics and associated muscle activity in people with symptoms of shoulder impingement, Phys Ther, 2000, 80(3):276-291. Level of Evidence: 3B.
- ↑ 56.0 56.1 Rosa DP et al., Effect of seated thoracic manipulation on changes in scapular kinematics and scapulohumeral rhythm in young asymptomatic participants: a randomized study, J Manipulative Physio Ther., 2013 Oct;36(8)546-54. Level of Evidence: 1B.
- ↑ Kon Y et al., The influence of handheld weight on the scapulohumeral rhythm, J Shoulder Elbow Surg. 2008 Nov-Dec; 17(6):943-946. Level of Evidence: 3B.
- ↑ McQuade KJ et al., Effects of local muscle fatigue on three-dimensional scapulohumeral rhythm, Clin Biomech., 1995 Apr;10(3): 144-148. Level of Evidence: 2C.