Electromyographic analysis of shoulder muscles of men with low-level paraplegia during a weight relief raise.

The purpose of this study was to define the demand on the shoulder musculature during performance of a weight relief raise. Intramuscular electromyographic activity of 12 shoulder muscles was recorded in 13 pain-free subjects with paraplegia while elevating the trunk from a sitting position. Upper extremity motion was determined by elbow electrogoniometry and video recordings. Three phases of the raise were analyzed: initial loading, lift, and hold. During the lift phase, high level triceps long head activity (54% manual muscle test [MMT]) produced elbow extension, whereas moderate- to high-level activity of the sternal pectoralis major (32% MMT) and latissimus dorsi (58% MMT) elevated the trunk on the fixed humerus. Deltoid, supraspinatus, infraspinatus, subscapularis, middle trapezius, serratus anterior, and biceps long head played minimal roles (< 25% MMT). Thoracohumeral muscle activity, by transferring the load on the humerus directly to the trunk, functionally circumvented the glenohumeral joint. This would reduce the potential for impingement of the rotator cuff.