Which of the following is NOT a prime mover for shoulder flexion?

• A. Latissimus dorsi
• B. Anterior deltoid
• C. Coracobrachialis
• D. Pectoralis major

Answer: (A)

The key idea is which muscles actively shorten to lift the arm forward at the shoulder. For shoulder flexion, the main players are the anterior part of the deltoid, the clavicular portion of the pectoralis major, and the coracobrachialis—they actively bring the humerus forward.

The latissimus dorsi, on the other hand, is a powerful extender, adductor, and internal rotator of the shoulder. Its pull tends to pull the arm backward and downward, opposing forward flexion. Because of that line of pull, it does not act as a prime mover during shoulder flexion. It can contribute in other ways or assist in certain postures, but it is not the primary driver of lifting the arm in front of the body.