The upper fibers of the pectoralis major primarily cause which movement?

• A. Flex the shoulder
• B. Extend the shoulder
• C. Abduct the shoulder
• D. Adduct the shoulder

Answer: (A)

The upper fibers of the pectoralis major pull the humerus forward and upward across the chest, creating shoulder flexion, especially from a neutral or extended position. They’re oriented to bring the arm in front of you, and while they can assist with moving the arm toward the midline, their main action is flexion. Abduction is primarily from the deltoid and supraspinatus, extension from muscles like the latissimus dorsi and posterior deltoid, and adduction is mainly a broader action of the chest muscles with the sternocostal fibers contributing more here. So flexing the shoulder best describes what the upper fibers chiefly do.