End range eccentric antagonist/concentric agonist strength ratios: a new perspective in shoulder strength assessment

The dynamic muscle stabilizers of the shoulder are critical to high performance in the overhead athlete. Previous evaluations of shoulder strength have focused on the concentric strength of the rotator cuff. Functionally, the rotator cuff muscles interact in an eccentric/concentric fashion. This is the first study to evaluate the end range eccentric antagonist/concentric agonist ratios of the shoulder rotators. Seventy-five asymptomatic college-level males were tested through a range of 20 degrees of lateral rotation to 90 degrees of medial rotation using the Kin-Com computer-assisted, hydraulic-resisted, isokinetic dynamometer at a speed of 90 degrees/sec. The end range (60-90 degrees) ratios for the medial rotators functioning eccentrically and lateral rotators functioning concentrically were 2.39:1 and 2.15:1 for the dominant and nondominant shoulders, respectively. End range (10 degrees of lateral rotation-20 degrees of medial rotation) ratios for lateral rotators functioning eccentrically and medial rotators functioning concentrically were 1.08:1 and 1.05:1 for the dominant and nondominant shoulders, respectively. The application of this functional assessment of strength testing results may provide important information in the evaluation of the injured shoulder in the overhead athlete, for prescreening, and to gauge return to sports after injury or surgery.