The supinator longus is commonly known as the brachioradialis muscle. It originates two-thirds of the way down the humerus (upper arm bone) between the triceps and the brachialis. The muscle begins wide and flat and twists toward the front of the arm as it descends. It then widens and flattens again before ending in a flat tendon, which inserts on the thumb side of the radius. Unlike most of the long tendons of the forearm, the tendon does not cross the wrist joint, but rather ends at the distal end of the radius. This muscle bends the forearm at the elbow. It does not assist in supination or pronation (turning the forearm).
