Which muscle performs flexion, adduction, and medial rotation of the shoulder?

Which muscle performs flexion, adduction, and medial rotation of the shoulder?

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

Answer: (A)

This question tests how a muscle’s attachments and fiber directions determine its actions at the shoulder. The Pectoralis major crosses the front of the shoulder and attaches to the humerus. Its clavicular (upper) fibers pull the arm forward to flex the shoulder, while its sternocostal (lower) fibers pull the arm toward the midline (adduction) and rotate the humerus inward (medial rotation). Because this single muscle has both flexor and adductor/rotator components, it can produce flexion, adduction, and medial rotation of the shoulder. Other muscles either don’t primarily perform all three actions together (for example, the deltoid mainly abducts; latissimus dorsi mainly extends, adducts, and medially rotates; supraspinatus initiates abduction), making the Pectoralis major the best fit for this combination.

This question tests how a muscle’s attachments and fiber directions determine its actions at the shoulder. The Pectoralis major crosses the front of the shoulder and attaches to the humerus. Its clavicular (upper) fibers pull the arm forward to flex the shoulder, while its sternocostal (lower) fibers pull the arm toward the midline (adduction) and rotate the humerus inward (medial rotation). Because this single muscle has both flexor and adductor/rotator components, it can produce flexion, adduction, and medial rotation of the shoulder. Other muscles either don’t primarily perform all three actions together (for example, the deltoid mainly abducts; latissimus dorsi mainly extends, adducts, and medially rotates; supraspinatus initiates abduction), making the Pectoralis major the best fit for this combination.