Shoulder Retractor Strengthening Exercise to Minimize Rhomboid Muscle Activity and Subacromial Impingement

PURPOSE We investigated the best position for shoulder retractor strengthening exercise to maximize middle trapezius activity and minimize rhomboid major activity. Although both trapezius and rhomboids are scapular retractors, rhomboids also act as downward rotators of the scapula, which can worsen subacromial impingement. METHODS Twelve healthy participants (age 30 [SD 6] y) with no history of shoulder pain were recruited for this study, which used fine-wire electromyography to examine maximal muscle activation of the middle trapezius and rhomboid major muscle fibres in four different positions: with the shoulder in 90° abduction with elbow completely extended and (1) shoulder internal rotation, (2) shoulder neutral rotation, (3) shoulder external rotation, and (4) rowing (shoulder neutral rotation and elbow flexed 90°). The ratio of trapezius to rhomboid muscles was compared with Wilcoxon signed-rank tests. RESULTS Muscle activation ratio during shoulder retraction exercise was significantly lower by 22% (i.e., rhomboid was more active than middle trapezius) when performed with the shoulder in rowing position (elbow flexed) than with the shoulder in external rotation (elbow extended) position (p=0.031). All four positions produced coactivation of trapezius and rhomboids. DISCUSSION Rowing position may not be the best position for shoulder retractor strengthening in patients with impingement syndrome. The preferable position for maximizing middle trapezius activity and minimizing rhomboid activity may be shoulder external rotation with elbow extended.