Shoulder terminal range eccentric antagonist/concentric agonist strength ratios in overhead athletes

Abstract

The agonist-antagonist strength relationship for shoulder external rotation and internal rotation was formerly described by the relatively more functional ratios of eccentric external rotator to concentric internal rotator moments, and eccentric internal rotator to concentric external rotator moments for the entire range of motion. The aim of this study was to provide descriptive data for terminal range eccentric antagonist/concentric agonist rotator cuff strength in overhead athletes. The dominant and non-dominant shoulders of 40 asymptomatic military overhead athletes were tested through a range of 20 degrees of external rotation to 90 degrees of internal rotation using the Cybex NORM isokinetic dynamometer at a speed of 90 degrees /s. Differences between the dominant and non-dominant shoulders were assessed using the paired samples t-test. The terminal range ratios during external rotation (20 degrees of internal rotation - 10 degrees of external rotation) were found to be 2.09 and 1.58 for the dominant and non-dominant shoulders, respectively, whereas the terminal range ratios during internal rotation (60-90 degrees of internal rotation) were 1.03 and 1.19 for the dominant and non-dominant shoulders, respectively. These ratio differences between the dominant and non-dominant shoulders were significant (P<0.01 for external and internal rotation). The muscle torque ratios of eccentric antagonist/concentric agonist are different between dominant and non-dominant shoulders of skilled overhead athletes at terminal ranges. This functional assessment of strength testing that reflects dynamic shoulder joint stability during the throwing activity at these specific ranges may provide valuable information either during preventive exercise programs or in the evaluation of the injured shoulder of the overhead athlete. We recommended functional exercises that improve eccentric external rotation strength on the dominant shoulder during the rehabilitation and prevention programs in overhead athletes.