Which elbow flexor is most powerful when the forearm is in neutral?

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

Answer: (B)

When you flex the elbow with the forearm in a neutral position, the muscle that produces the largest bending torque is the brachioradialis. Its line of pull is most favorable in neutral, giving it a strong moment arm across the elbow and allowing it to generate substantial elbow flexion without needing the forearm to be rotated into supination or pronation.

The biceps brachii, while very powerful, relies on forearm supination to maximize its elbow-flexing torque; in a neutral position its contribution is not as great. The brachialis is a strong pure elbow flexor across positions, but in neutral the brachioradialis tends to contribute more to the flexion moment. The pronator teres mainly pronates the forearm and is a relatively weak elbow flexor, so it isn’t the best option for powerful elbow flexion in neutral.