forearm
Brachioradialis labeled at center left, sixth from the top. The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm.
The muscles of the upper arm are responsible for the flexion and extension of the forearm at the elbow joint. Flexion of the forearm is achieved by a group of three muscles — the brachialis, biceps brachii, and brachioradialis. ... Most of the muscles that move the wrist, hand, and fingers are located in the forearm.