Effects of Different Shoulder Horizontal Adduction Angles on Muscle Activity of the Shoulder External Rotators during Prone Shoulder External Rotation

<p>Objective: This study aimed to investigate the effect of different shoulder horizontal adduction angles on the muscle activity of the shoulder external rotators during Prone Shoulder External Rotation (PSER).</p><p>Methods: Twelve healthy males participated in this study. The exercise involved maintaining an isometric contraction of the shoulder at 90° external rotation in 90° abduction. Muscle activity during PSER was measured in the infraspinatus, teres minor, and posterior deltoid muscles. PSER was performed at three different shoulder horizontal adduction angles: 0°, 15°, and 30°. The muscle activities of three muscles were compared among the three conditions in PSER.</p><p>Results: There was no significant difference in muscle activity of the infraspinatus and teres minor muscles among the three conditions. However, muscle activity of the posterior deltoid muscle was significantly decreased at PSER with horizontal adduction angles 30° compared to 0° (p = 0.003, d = 0.95).</p><p>Conclusion: This study indicated that PSER with horizontal adduction angle 30° suppressed muscle activity of the posterior deltoid muscle, while no decrease was observed in the muscle activity of the infraspinatus and teres minor muscles.</p>