In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius.

[1] The supinator consists of two planes of fibers, between which passes the deep branch of the radial nerve.

The upper fibers (pars profunda) of the deeper plane form a sling-like fasciculus, which encircles the neck of the radius above the tuberosity and is attached to the back part of its medial surface; the greater part of this portion of the muscle is inserted into the dorsal and lateral surfaces of the body of the radius, midway between the oblique line and the head of the bone.

The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle—an arrangement that can lead to entrapment and compression of the deep part, potentially resulting in selective paralysis of the muscles served by this nerve (the extensor muscles and the abductor pollicis longus.

This article incorporates text in the public domain from page 454 of the 20th edition of Gray's Anatomy (1918)