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 degrees and the elbow flexed to 90 degrees.

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.