Shoulder antagonistic strength ratios during concentric and eccentric muscle actions in the scapular plane

Reporting agonist/antagonist ratios is frequently more clinically applicable than reporting absolute strength values of single muscle groups. The purpose of this study was to measure shoulder abduction/adduction and external/internal rotation ratios in the functional scapular plane of shoulder movement. Ratios were calculated using peak and average torques during concentric and eccentric muscle actions, and ratios of healthy males and females were compared. Thirty-six, non-athletic subjects performed concentric-eccentric cycles at two angular velocities. No significant differences were observed in the ratios using peak and average torques as criterion measurements. Abduction/adduction ratios using peak torques were significantly greater during concentric than eccentric actions. External/internal rotation ratios using average torques were significantly greater during eccentric than concentric actions. External/internal rotation ratios at 180 degrees/sec were significantly greater than those at 90 degrees/sec. No significant differences were observed between male and female subjects. Ratios were higher than previously reported. This was attributed to the scapular plane testing position. The clinician should be aware that shoulder strength ratios are dependent on position and that the scapular plane may be advantageous in some cases for testing and treatment.