Strategies for controlling axial shoulder rotation change shoulder muscle activity during external rotation exercises

Abstract

The infraspinatus muscle has a crucial role in shoulder stability. Although axial shoulder rotation is useful for selective activation of the infraspinatus, no study has examined the influence of exercise position on axial shoulder rotation during shoulder external rotation (ER) exercises. Thus, this study investigated the muscle activity in the infraspinatus, posterior deltoid, and middle trapezius during shoulder ER exercises performed with and without controlled axial shoulder rotation in 2 different positions. Twenty healthy subjects performed prone external rotation (PER) exercises with and without pressure biofeedback and seated external rotation (SITER) exercises with and without posterior humeral head gliding. Muscle activity during each ER exercise was measured using surface electromyography. Exercise strategy (P < .001) and position (P < .001) had a significant main effect on muscle activity in the infraspinatus and posterior deltoid. However, no significant interaction between strategy and position was observed. For muscle activity in the middle trapezius, strategy and position had a significant interaction effect (P = .014). Muscle activity in the infraspinatus increased significantly with the use of strategies to control axial shoulder rotation, whereas muscle activity in the posterior deltoid and middle trapezius decreased significantly. For all 3 muscles, greater activity was observed in the prone position than the seated position. We suggest that PER with pressure biofeedback can be useful to improve selective activation of the infraspinatus muscle while further eliciting infraspinatus muscle activity.