An Electromyographic Evaluation of Subdividing Active-Assistive Shoulder Elevation Exercises

Abstract

Background: Active-assistive range of motion exercises to gain shoulder elevation have been subdivided into gravity-minimized and upright-assisted exercises, yet no study has evaluated differences in muscular demands. Hypothesis: Compared with gravity-minimized exercises, upright-assisted exercises will generate larger electromyographic (EMG) activity. Compared with all active-assistive exercises, upright active forward elevation will generate more EMG activity. Study design: Controlled laboratory study. Methods: Fifteen healthy individuals participated in this study. The supraspinatus, infraspinatus, and anterior deltoid were evaluated. The independent variables were 11 exercises performed in random order. The dependent variable was the maximum EMG amplitude of each muscle that was normalized to a maximal voluntary isometric contraction (MVIC). Results: Each muscle demonstrated significant differences between exercises ( P < .001), with upright active forward elevation producing the greatest EMG for all muscles (95% confidence interval [CI], 12% to 50% MVIC). The orders of exercise varied by muscle, but the 5 gravity-minimized exercises always generated the lowest EMG activity. The upright-assisted exercises (95% CI, 23% to 42% MVIC) for the anterior deltoid generated more EMG activity than did the gravity-minimized exercises (95% CI, 9% to 21% MVIC) ( P < .05). The infraspinatus and supraspinatus demonstrated increasing trends in EMG activity from gravity minimized to upright assisted ( P > .05). Conclusion: The results suggest a clear distinction between gravity-minimized exercises and upright-assisted exercises for the anterior deltoid but not for the supraspinatus and infraspinatus. Between the 2 types of assisted exercises, the results also suggest a clear distinction in terms of active elevation of the arm for the supraspinatus and anterior deltoid but not for the infraspinatus. Clinical Relevance: Muscle activation levels increase as support is removed, but subdivision of active-assistive range of motion to protect the supraspinatus and infraspinatus may not be necessary.