Moment arms of the shoulder muscles during axial rotation

Abstract

The objective of the present study was to determine the instantaneous moment arms of 18 major muscle sub-regions crossing the glenohumeral joint in axial rotation of the humerus during coronal-plane abduction and sagittal-plane flexion. The tendon-excursion method was used to measure instantaneous muscle moment arms in eight entire upper-extremity cadaver specimens. The results showed that the inferior subscapularis was the largest internal rotator; its rotation moment arm peaks were 24.4 and 27.0 mm during abduction and flexion, respectively. The inferior infraspinatus and teres minor were the greatest external rotators; their respective rotation moment arms peaked at 28.3 and 26.5 mm durin..