The Effect of Muscle Fatigue on Muscle Force-Couple Activation of the Shoulder

Context: Muscle fatigue is an important concept in regard to the muscle function of the shoulder joint. Its effect on the muscle force couples of the glenohumeral joint has not been fully identified. Objective: To examine the effects of muscle fatigue on muscle force-couple activation in the normal shoulder. Design: Pretest, posttest. Patients: Ten male subjects, age 18–30 years, with no previous history of shoulder problems. Main Outcome Measures: EMG (area) values were assessed for the anterior and middle deltoid, subscapularis, and infraspinatus muscles during 4 dynamic stabilizing exercises before and after muscle fatigue. The exercises examined were a push-up, horizontal abduction, segmental stabilization, and rotational movement on a slide board. Results: No significant differences were observed for any of the muscles tested. Conclusions: The results of our study indicate that force-couple coactivation of the glenohumeral joint is not significantly altered after muscle fatigue.