What is the function of biceps brachii?

• A. Elbow extension
• B. Elbow flexion
• C. Shoulder rotation
• D. Wrist extension

Answer: (B)

Bending the elbow is the main action of the biceps brachii. This two-headed muscle sits on the front of the upper arm and crosses the elbow, so when it contracts it pulls the forearm up toward the upper arm, producing elbow flexion. It also helps rotate the forearm (supination), especially when the elbow is bent. It does not extend the elbow (that’s the job of the triceps), it doesn’t primarily rotate the shoulder, and it doesn’t extend the wrist (those are controlled by other shoulder and forearm muscles). A practical way to feel it is when you perform a biceps curl—the bending of the elbow is driven by this muscle.