Which muscles are the prime movers for shoulder extension?

Which muscles are the prime movers for shoulder extension?

• A. Anterior deltoid
• B. Pectoralis major and Subscapularis
• C. Infraspinatus and Teres minor
• D. Latissimus dorsi, Teres major, and Posterior deltoid

Answer: (D)

Shoulder extension is the movement of pulling the arm backward, and the primary actors are the muscles that pull the humerus posteriorly and, with their lines of pull, extend the shoulder joint. The latissimus dorsi and teres major are powerful extensors that originate on the trunk and insert into the humerus; when they contract, they pull the arm backward and inward, making them the main contributors to shoulder extension. The posterior deltoid lies on the back of the shoulder and provides extension as well, especially when the arm is in positions where extension is most needed (such as with the arm moving from a flexed or abducted starting point). Together, these three produce the strongest and most consistent shoulder extension. The other muscles don’t serve this primary role. The anterior deltoid flexes the shoulder, not extends. Pectoralis major can assist with extension only in specific positions and is more commonly known for flexion, adduction, and internal rotation. Subscapularis mainly internal rotates the humerus, while infraspinatus and teres minor are external rotators with stabilizing actions rather than primary extensor movers.

Shoulder extension is the movement of pulling the arm backward, and the primary actors are the muscles that pull the humerus posteriorly and, with their lines of pull, extend the shoulder joint. The latissimus dorsi and teres major are powerful extensors that originate on the trunk and insert into the humerus; when they contract, they pull the arm backward and inward, making them the main contributors to shoulder extension. The posterior deltoid lies on the back of the shoulder and provides extension as well, especially when the arm is in positions where extension is most needed (such as with the arm moving from a flexed or abducted starting point). Together, these three produce the strongest and most consistent shoulder extension.

The other muscles don’t serve this primary role. The anterior deltoid flexes the shoulder, not extends. Pectoralis major can assist with extension only in specific positions and is more commonly known for flexion, adduction, and internal rotation. Subscapularis mainly internal rotates the humerus, while infraspinatus and teres minor are external rotators with stabilizing actions rather than primary extensor movers.