THE FUNCTION OF THE LONG HEAD OF THE BICEPS AT THE SHOULDER 267

Abstract

The purpose of this study was to delmeate, through EMG analysis, the function of the long head of the biceps at the shoulder and to determine the specificity of manual muscle tests currently used to isolate biceps pathology at the shoulder. The shoulders of 10 subjects were examined dynamically with integrated EMG (IEMG). The long head of the biceps was instrumented with thin wire electrodes. The supraspinatus, infraspinatus, deltoid, brachialis and brachioradialis were similarly instrumented as controls. As the biceps functions primarily as a forearm supinator and elbow flexor, a brace was used to lock the elbow in extension with the forearm in neutral pronation/supination. Shoulder flexion, extension, internal and external rotation were tested in a full arc at fast (180°/sec) and slow(36°/sec) speeds with and without a 5 lb weight attached to the distal end of the brace. The brace was removed and manual muscle tests (Speed's, Yergason's and elbow flexion against resistance at 90° abduction), that are assumed to isolate bicipital activity at the shoulder were evaluated. The brachialis and brachioradialis confirmed the lack of active elbow flexion in the brace. We found that no IEMG activity was evident at the long head of the biceps muscle in response to any of the isolated shoulder motions. The deltoid, supraspinatus and infraspinatus were all variable active according to the specific motion. Yergason's, Speed's and elevated flexion testing produce high amplitude signal not only in the biceps leads, but across the supraspinatus, infraspinatus and deltoid muscles as well. The data demonstrates that the long head of the biceps is not active in isolated shoulder motion when the elbow and forearm are controlled. Any hypothesis on bicipital function at the shoulder must be based on either a passive role of the tendon or an active role that achieves tension in association with elbow and forearm activity. Manual muscle testing for the biceps is not specific for biceps pathology at the shoulder.