Which muscles assist shoulder extension in addition to the primary movers?

• A. Latissimus Dorsi alone
• B. Anterior Deltoid and Pectoralis Major
• C. Posterior Deltoid, Latissimus Dorsi, and Teres Major
• D. Biceps Brachii and Brachialis

Answer: (C)

Extending the shoulder involves moving the arm backward, and the primary shoulder extensors are the latissimus dorsi and the posterior deltoid. Teres major also assists in this motion, especially when the movement is resisted or the arm is in a certain position, making it a synergist in shoulder extension. Therefore, muscles that assist shoulder extension in addition to the primary movers are the posterior deltoid, latissimus dorsi, and teres major. The anterior deltoid and pectoralis major are geared toward flexion and internal rotation, not extension, so they don’t contribute to this motion. The biceps brachii and brachialis focus on elbow flexion and do not extend the shoulder, so they don’t fit as assisting movers for shoulder extension.