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This Article Full Text Full Text (PDF) All Versions of this Article: 32/4/1013    most recent 0363546503262190v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Request Reprints Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Myers, J. B. Articles by Lephart, S. M. Search for Related Content PubMed PubMed Citation Articles by Myers, J. B. Articles by Lephart, S. M. Related Collections Dislocations Shoulder Rehabilitation/Training

Reflexive Muscle Activation Alterations in Shoulders With Anterior Glenohumeral Instability

Joseph B. Myers, PhD, ATC^*,, Yan-Ying Ju, PhD, PT, ATC, Ji-Hye Hwang, MD, PhD, Patrick J. McMahon, MD, Mark W. Rodosky, MD and Scott M. Lephart, PhD, ATC

From the University of Pittsburgh, Pittsburgh, Pennsylvania, Chang Gung University, Taoyuan, Taiwan, and the Samsung Medical Center, Sungkyunkwan University, Seoul, Korea

^* Address correspondence to Joseph B. Myers, Neuromuscular Research Laboratory, UPMC Center for Sports Medicine, 3200 South Water Street, Pittsburgh, PA 15203 (e-mail: myersjb{at}msx.upmc.edu).

Background: Patients with glenohumeral instability have proprioceptive deficits that are suggested to contribute to muscle activation alterations.

Hypothesis: Muscle activation alterations will be present in shoulders with anterior glenohumeral instability.

Study Design: Posttest-only control group design.

Methods: Eleven patients diagnosed with anterior glenohumeral instability were matched with 11 control subjects. Each subject received an external humeral rotation apprehension perturbation while reflexive muscle activation characteristics were measured with indwelling electromyography and surface electromyography.

Results: Patients with instability demonstrated suppressed pectoralis major and biceps brachii mean activation; increased peak activation of the subscapularis, supraspinatus, and infraspinatus; and a significantly slower biceps brachii reflex latency. Supraspinatus-subscapularis coactivation was significantly suppressed in the patients with instability as well.

Conclusions and Clinical Relevance: In addition to the capsuloligamentous deficiency and proprioceptive deficits present in anterior glenohumeral instability, muscle activation alterations are also present. The suppressed rotator cuff coactivation, slower biceps brachii activation, and decreased pectoralis major and biceps brachii mean activation may contribute to the recurrent instability episodes seen in this patient group. Clinicians can implement therapeutic exercises that address the suppressed muscles in patients opting for conservative management or rehabilitation before and after capsulorraphy procedures.

Key Words: instability • reflexes • electromyography • shoulder

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