Electromyographic study of the m. biceps brachii in movements at the glenohumeral joint.

Our electromyographic studies on the participation of the m. biceps brachii in the movements of the glenohumeral joint, performed in 20 young adult male volunteers, permit the following conclusions: (1) In the movement of arm flexion, performed against resistance and with extended elbow, both the long and the short heads of the m. biceps brachii were active in all 30 volunteers examined. (2) The same movement of the arm, arm flexion with extended elbow, now without resistance, that is to say performed freely, showed both the long and short heads of the m. biceps brachii active in the majority of cases. (3) In the movements of arm extension, performed freely and aganst resistance, with extended elbow, and also in the movement of lateral arm rotatin with flexed elbow, with and without resistance, the m. biceps brachii was absolutely inactive in all 30 volunteers examined. (4) In the movement of arm abduction, with extended elbow, the element of resistance to the performance showed itself to be important, since without it the m. biceps brachii was absolutely inactive; in the movement performed against resistance both heads of the muscle showed activity in 3 out of the 30 volunteers tested. (5) In the movements of arm abduction with and without resistance, with flexed elbow, the m. biceps brachii was active on occasion. (6) In the Movements of arm adduction against resistance, with the elbow either flexed or extended, it was only the short head of the m. biceps brachii which was active, and this in half of the cases examined. (7) In the movements of medical rotation of the arm, with extended elbow, performed freely or against resistance, the long and the short heads of the m. biceps brachii each showed a different behaviour: the long head was always inactive, whereas the short one was seldom active.