Which muscle is the primary extensor of the forearm at the elbow joint?

• A. Biceps brachii
• B. Triceps brachii
• C. Brachialis
• D. Brachioradialis

Answer: (B)

Verified step by step guidance

1. Identify the action described in the problem: extension of the forearm at the elbow joint. Extension means increasing the angle between the forearm and the upper arm.
2. Recall the main muscles involved in movements at the elbow joint: Biceps brachii, Brachialis, Brachioradialis, and Triceps brachii.
3. Understand the primary functions of each muscle: Biceps brachii primarily flexes the forearm and supinates the hand; Brachialis is a strong flexor of the forearm; Brachioradialis assists in flexion, especially when the forearm is in a mid-pronated position.
4. Recognize that the Triceps brachii is the main muscle responsible for extending the forearm at the elbow joint, meaning it straightens the arm by increasing the angle at the elbow.
5. Conclude that the primary extensor of the forearm at the elbow joint is the Triceps brachii.