The elbow joint consists of the humers (upper arm bone), radius and ulna in the forearm. The ulna is the bone on the little finger side of the forearm (remember l in ulna for little finger) and the radius radiates around it. The muscles at the elbow joint are the biceps brachii, brachialis, brachioradialis, triceps brachii (triceps muscle), anconeus, pronator teres, pronator quadratus and supinator.
The Biceps brachii crosses both the elbow and shoulder joints. It is a weak flexor of the shoulder joint but is a strong flexor the elbow joint, especially when the forearm is supinated (palm facing up).
The supinator muscle assists Biceps brachii in supinating the hand, that is turning it over so that the palm faces up. To isolate the supinator muscle, supinate the hand whilst extending the elbow as this takes out the Biceps muscle.