Function of the song head of the biceps at the shoulder: Electromyographicanalysis

The purpose of this study was to delineate, through electromyographic analy sis, the function of the long head of the biceps at the shoulder Ten should ers were examined with dynamic electromyography. The long head of the bicep s was instrumented with thin wire electrodes. The supraspinatus, infraspina tus, deltoid, brachialis, and brachioradialis were instrumented as controls . Because the biceps functions primarily as a forearm supinator and elbow f lexor, a long arm brace was used to lock the elbow in extension with the fo rearm in neutral pronation/supination. Each motion was tested in a full are at fast (170 degrees per second) and slow (36 degrees per second) speeds a nd repeated with and without a 5-pound weight attached to the distal end of the brace. No electrical activity was identified in the long head of the b iceps muscle in response to isolated shoulder motion with the elbow and for earm position controlled. The data demonstrate that the long head of the bi ceps is not active in isolated shoulder motion when the elbow and forearm a re controlled. Thus, any hypothesis on bicipital function at the shoulder m ust be based on either a passive role of the tendon or tension in associati on with elbow and forearm activity.