Which muscle is a prime mover for Forearm Supination?

Which muscle is a prime mover for Forearm Supination?

• A. Brachioradialis
• B. Biceps brachii
• C. Supinator
• D. Pronator teres

Answer: (C)

Supination of the forearm is turning the palm to face upward by rotating the radius around the ulna. The muscle that directly drives this rotation is the supinator. It lies at the top of the forearm, wraps around the radius, and pulls it into a supinated position when it contracts, making it the primary mover for forearm rotation, especially when the elbow is extended. The biceps brachii can also produce strong supination, and it is particularly powerful when the elbow is flexed around 90 degrees, but its effectiveness as a prime mover depends on that elbow position, not on a constant, primary rotation action. Pronator teres does the opposite, pronating the forearm, so it wouldn’t be the primary muscle responsible for supination. Brachioradialis mainly flexes the elbow and only assists with supination in certain forearm positions, not as the primary rotator.

Supination of the forearm is turning the palm to face upward by rotating the radius around the ulna. The muscle that directly drives this rotation is the supinator. It lies at the top of the forearm, wraps around the radius, and pulls it into a supinated position when it contracts, making it the primary mover for forearm rotation, especially when the elbow is extended. The biceps brachii can also produce strong supination, and it is particularly powerful when the elbow is flexed around 90 degrees, but its effectiveness as a prime mover depends on that elbow position, not on a constant, primary rotation action. Pronator teres does the opposite, pronating the forearm, so it wouldn’t be the primary muscle responsible for supination. Brachioradialis mainly flexes the elbow and only assists with supination in certain forearm positions, not as the primary rotator.