Which action is performed by the biceps brachii?

• A. Flex the elbow
• B. Extend the elbow
• C. Flex the shoulder
• D. Pronate the forearm

Answer: (A)

The biceps brachii is best understood as a two-joint muscle whose most characteristic job is elbow flexion. When the forearm is in a supinated position, the biceps actively bends the elbow, pulling the forearm toward the upper arm. This makes elbow flexion the primary action people rely on when activating the biceps. It does help with forearm supination because of its attachment to the radius, but that function doesn’t define its main action.

The biceps can contribute to shoulder movement since it crosses the shoulder, but the primary movers of shoulder flexion are other muscles like the deltoid and pectoralis major, with the biceps playing a secondary role. Extending the elbow is carried out mainly by the triceps brachii, and pronating the forearm is performed by the pronator muscles, not the biceps (which is most effective when the forearm is supinated).