Supinator

The supinator is a small, broad, flat muscle of the forearm that belongs to its posterior compartment, lying in the deep part. It is located at the proximal end of the forearm, encircling the upper one-third of the radius. As its name suggests, this muscle supinates the forearm at the proximal radioulnar joint. It acts as an antagonist to the pronator teres and pronator quadratus muscles.