Name the primary forearm pronators.

• A. Pronator teres and pronator quadratus
• B. Supinator
• C. Brachioradialis and brachialis
• D. Flexor carpi radialis and flexor carpi ulnaris

Answer: (A)

Forearm pronation is produced by rotating the radius around the ulna, and the primary muscles that do this are the two that specifically pull the radius over the ulna. The main one is the pronator quadratus, a deep square muscle at the distal forearm that directly twists the radius against the ulna to rotate the forearm. The other key pronator is the pronator teres, which crosses the elbow and forearm and assists with pronation while also helping with elbow flexion. Together, these two generate the bulk of pronation.

The opposing muscle, the supinator, works to rotate the forearm back to a palms-up position, so it’s not a pronator. Muscles like the brachioradialis and brachialis are elbow flexors and don’t primarily contribute to forearm rotation. The wrist flexors shown are involved in wrist movements, not forearm rotation.