Electromyographic Activity in the Immobilized Shoulder Girdle Musculature During Scapulothoracic Exercises

Abstract 

Smith J, Dahm DL, Kaufman KR, Boon AJ, Laskowski ER, Kotajarvi BR, Jacofsky DJ. Electromyographic activity in the immobilized shoulder girdle musculature during scapulothoracic exercises.

Objective

To quantify the electromyographic activity in the shoulder girdle musculature during scapulothoracic exercises performed in a shoulder immobilizer in asymptomatic men.

Design

Descriptive.

Setting

Motion analysis laboratory at a tertiary care center.

Participants

Five asymptomatic male volunteers ages 24 to 32 years.

Intervention

Fine-wire (supraspinatus, infraspinatus, upper subscapularis) and surface (deltoids, trapezii, biceps, serratus anterior) electrodes recorded electromyographic activity from each muscle during scapular clock, elevation, depression, protraction, and retraction exercises completed during a single testing session in random order.

Main Outcome Measure

Mean peak normalized (percentage of maximal voluntary contraction [MVC]) electromyographic activity of each muscle during each exercise.

Results

Biceps activity was uniformly low (<20% MVC), whereas upper subscapularis activity was uniformly high (40%−63% MVC). Both scapular depression and protraction elicited low activity (<20% MVC) in the supraspinatus, infraspinatus, anterior deltoid, and biceps brachii muscles, while generally producing greater than 20% MVC activity in the trapezii and serratus. Scapular depression produced the largest serratus anterior activity (47% MVC).

Conclusions

These data are the first to describe the electromyographic activity during scapulothoracic exercises while in a shoulder immobilizer. Based on electrophysiologic data in normal volunteers, our findings suggest that during periods of shoulder immobilization: (1) scapular depression and protraction exercises could potentially be safely performed after rotator cuff repair to facilitate scapulothoracic rehabilitation, (2) all exercises studied could potentially be safe after superior labral anteroposterior shoulder repair, and (3) all exercises studied should be avoided after subscapularis repair. Further investigation in symptomatic individuals may facilitate refinement of these recommendations.

Key Words:  Electromyography , Exercise , Rehabilitation , Scapula , Shoulder