Which muscle is the primary agonist responsible for extension of the elbow joint?

• A. Brachialis
• B. Biceps brachii
• C. Triceps brachii
• D. Pronator teres

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the term 'agonist' in muscle movement. The agonist is the primary muscle responsible for producing a specific movement at a joint.
2. Step 2: Identify the movement in question, which is extension of the elbow joint. Extension refers to straightening the elbow, increasing the angle between the forearm and upper arm.
3. Step 3: Recall the main muscles involved in elbow movement. The biceps brachii and brachialis primarily perform elbow flexion (bending the elbow), while the triceps brachii is responsible for elbow extension.
4. Step 4: Analyze the options given: Brachialis and biceps brachii are flexors, pronator teres is involved in forearm pronation, and triceps brachii is the only muscle that extends the elbow.
5. Step 5: Conclude that the triceps brachii is the primary agonist muscle responsible for extension of the elbow joint.