Infraspinatus Isolation During External Rotation Exercise at Varying Degrees of Abduction

Context:External rotation (ER) strengthening exercises are a common component of shoulder injury prevention and rehabilitation programs. They are primarily intended to target the infraspinatus muscle, based on its role in glenohumeral stabilization and inferior humeral glide. ER also recruits the posterior deltoid, which can be undesirable due to its role in subacromial space narrowing. Objective:To determine the angle of humeral abduction that maximizes the infraspinatus to posterior deltoid activation ratio (INFRA/PD) during ER. Design:Within-subjects repeated-measures controlled laboratory trial. Participants:10 healthy participants (5 male, 5 female) aged 21±0.67 years. Intervention:7 consecutive repetitions of ER at 7 different abduction angles ranging from 0o-90o, with resistance normalized to 3% body mass. Main Outcome Measures:Surface electromyography (SEMG) was performed on the infraspinatus, middle deltoid and posterior deltoid. SEMG data were processed to determine absolute muscle activation as...