Which muscle extends, adducts, and medially rotates the shoulder?

Which muscle extends, adducts, and medially rotates the shoulder?

• A. Latissimus Dorsi
• B. Pectoralis Major
• C. Deltoid
• D. Infraspinatus

Answer: (A)

Latissimus dorsi is the muscle that can extend, adduct, and medially rotate the shoulder. When it contracts, it pulls the humerus backward (extension), toward the body's midline (adduction), and rotates the arm inward (medial rotation). This large back muscle originates along the lower spine and iliac crest and inserts into the intertubercular groove of the humerus, so its line of pull is well suited to produce those three actions together. It’s especially important in actions like pulling movements or climbing. Pectoralis major does adduct and medially rotate the shoulder, and it can contribute to extension from a flexed position, but it isn’t primarily an extensor. Deltoid mainly abducts the shoulder (middle fibers), and infraspinatus primarily externally rotates the shoulder. The combination of extending, adducting, and medially rotating points to latissimus dorsi as the best match.

Latissimus dorsi is the muscle that can extend, adduct, and medially rotate the shoulder. When it contracts, it pulls the humerus backward (extension), toward the body's midline (adduction), and rotates the arm inward (medial rotation). This large back muscle originates along the lower spine and iliac crest and inserts into the intertubercular groove of the humerus, so its line of pull is well suited to produce those three actions together. It’s especially important in actions like pulling movements or climbing.

Pectoralis major does adduct and medially rotate the shoulder, and it can contribute to extension from a flexed position, but it isn’t primarily an extensor. Deltoid mainly abducts the shoulder (middle fibers), and infraspinatus primarily externally rotates the shoulder. The combination of extending, adducting, and medially rotating points to latissimus dorsi as the best match.