Isokinetic Eccentric-to-Concentric Strength Ratios of the Shoulder Rotator Muscles in Throwers and Nonthrowers

Abstract

Background One of the possible mechanisms leading to shoulder injury may be a strength imbalance between those muscles that accelerate the upper limb and those responsible for deceleration. Many studies have examined shoulder balance through a concentric strength ratio of external and internal shoulder rotator muscles. Hypothesis A functional external eccentric-to-internal concentric ratio may be a better identifier of muscular imbalance in dominant and nondominant shoulders of throwers and nonthrowers. Study Design Controlled laboratory study. Methods Eccentric external and concentric internal peak torques were measured bilaterally in 59 men (16 throwers and 43 nonthrowers) at 300 deg/sec. Subjects were tested in the supine position with the shoulder abducted to 90° and the elbow flexed to 90°. Results Throwers exhibited significantly lower ratios than nonthrowers in their dominant limb; there was no difference between groups for the nondominant limb. Conclusions The lower ratio in the throwers’ dominant limb was attributed to significantly greater concentric internal rotation torques without concomitant eccentric external torque gains. Clinical Relevance Rehabilitation and injury prevention regimens that include functional exercises to improve eccentric external rotation strength may bring more balance to the dominant shoulder of throwing athletes.