The supinator muscle is a large, circular muscle located in the posterior (back) region of the forearm. It originates at the ulna (one of the bones in the forearm) and the interosseous membrane, and inserts into the radius (the other bone in the forearm) and the extensor muscles of the hand. The supinator muscle is one of the muscles that make up the extensor compartment of the forearm, and is located deep to the superficial muscles of the posterior forearm.

The main function of the supinator muscle is to supinate (rotate outward) the hand at the forearm. This movement is essential for activities such as turning the palm upwards, and helps to provide stability and support for the wrist and hand. The supinator muscle also helps to stabilize the wrist and hand, and assist in flexion (bending) of the hand.

In everyday life, the supinator muscle is used in many activities that involve supination of the hand, such as opening a jar or turning a doorknob. It is also used in activities that require stability and support for the wrist and hand, such as holding a heavy object or writing.