What is the primary action of the triceps brachii muscle at the elbow joint?

• A. Abduction of the arm at the shoulder
• B. Extension of the forearm at the elbow
• C. Supination of the forearm
• D. Flexion of the forearm at the elbow

Answer: (B)

Verified step by step guidance

1. Identify the anatomical location and function of the triceps brachii muscle. It is located on the posterior side of the upper arm, spanning from the scapula and humerus to the olecranon process of the ulna.
2. Recall the primary movement actions at the elbow joint, which include flexion and extension of the forearm.
3. Understand that the triceps brachii is the main extensor muscle of the forearm, meaning it straightens the elbow by increasing the angle between the forearm and the upper arm.
4. Compare the other options: abduction of the arm occurs at the shoulder joint and involves different muscles; supination involves rotating the forearm to turn the palm upward, primarily done by the supinator muscle and biceps brachii; flexion of the forearm is performed by muscles like the biceps brachii and brachialis.
5. Conclude that the primary action of the triceps brachii at the elbow joint is extension of the forearm, which matches the correct answer.