Supraspinatus and Deltoid: not just two arm elevators?
Although there is consensus on the function of the Deltoid as a primary elevator of the arm, this remains unclear in the case of the Supraspinatus: it has been pointed to as a contributor to glenohumeral abduction and elevation, but even more so as a stabilizer of the humeral head within the rotator cuff complex.
To gain insight in both roles of the Supraspinatus, this study used a transversal design in which 22 healthy subjects performed isometric abduction against small and large moment loading towards elevation. The humerus was placed in 30° of horizontal abduction, 60° of elevation and 45° of internal rotation and was supported by a splint to eliminate gravitational loading. EMG activity of the muscles was measured by either surface (Deltoid) or via fine-wire electrodes (Supraspinatus).
Deltoid activation, as expected, increased as a result of an increase in glenohumeral elevation moment, yet the response elicited in the Supraspinatus was highly variable. It is speculated that in different individuals, the Supraspinatus may have different tasks, contributing more to arm elevation or to stabilization of the humeral head.
> From: De Witte et al., Hum Mov Sci 33 (2015) 273-283. All rights reserved to Elsevier B.V. Click here for the Pubmed summary.