What are the primary actions of the triceps brachii?

• A. Elbow extension; long head assists shoulder extension and adduction.
• B. Elbow flexion; long head assists shoulder flexion.
• C. Forearm pronation; long head extends shoulder.
• D. Elbow extension; lateral head assists abduction.

Answer: (A)

The triceps brachii mainly acts to straighten the elbow. All three heads converge on the olecranon, so elbow extension is its primary action. The long head, because it crosses the shoulder joint, can also influence shoulder movements by helping to extend the arm and bring it toward the midline (adduction). That combination—elbow extension as the main action, plus the long head’s additional role in extending and adducting the shoulder—best describes its function.

Other proposed actions don’t fit: elbow flexion isn’t a function of the triceps (that’s done by the biceps and brachialis), forearm pronation isn’t controlled by the triceps, and abduction isn’t a primary action of the triceps (that movement is dominated by deltoid and related muscles).