Clarification of the role of the supraspinatus muscle in shoulder function.

The purpose of this study was to determine the torque produced by the supraspinatus muscle within the functional motion planes of forward flexion and elevation in the plane of the scapula. An isokinetic dynamometer was used to measure the reduction in torque produced by isolated paralysis of the suprascapular and axillary nerves in ten normal volunteers. A calculation of the potential torque of the supraspinatus and deltoid muscles was obtained from the product of the moment arm, cross-sectional area, and integrated electromyographic signal. The results of both the dynamometer measurement and the calculation of torque supported our conclusion that the supraspinatus and deltoid muscles are equally responsible for producing torque about the shoulder joint in the functional planes of motion.