An electromyographic study of some muscles crossing the elbow joint

Abstract Pairs of fine wire electrodes were inserted into the lateral, medial and long heads of the triceps brachii, into the anconeus, biceps brachii, brachialis and brachioradialis muscles. Each pair of electrodes was connected to an EMG integrator coupler in an eight channel recorder. Many movements and exercises were studied, and the relative contribution made by each muscle to any given movement was appraised. The anconeus initiates extension of the elbow and acts to maintain extension and to stabilize the elbow joint during other motions involving the upper extremity. The anconeus is responsible for fine control, but its activity frequently decreases when the more powerful triceps brachii contracts or when it loses its mechanical advantage at full extension. In pronation, the anconeus is very active; whereas during supination the anconeus is less active, and the triceps counteracts the powerful pull of the biceps brachii. The long head of the triceps also works as an adductor of the arm. When the triceps assists the anconeus in stabilizing the joint, the biceps brachii, brachialis and event the brachioradialis may contract to counteract any tendency to further extend the joint.