Which muscles compose the agonists for shoulder flexion?

• A. Latissimus Dorsi
• B. Pectoralis Major Upper Fibers, Deltoid Anterior, Biceps Brachii
• C. Supraspinatus
• D. Pectoralis Major Lower Fibers

Answer: (B)

Shoulder flexion is the movement of lifting the arm forward at the shoulder joint. The main muscles actively driving this are the anterior fibers of the deltoid and the clavicular (upper) portion of the pectoralis major, as they attach to the humerus in a way that pulls the arm forward and up. The biceps brachii also helps, especially when the elbow is flexed, because its long head crosses the shoulder and can assist in lifting the arm.

Other muscles listed don’t function as primary flexors: latissimus dorsi pulls the arm downward and backward (extension/adduction), supraspinatus mainly initiates abduction, and the lower fibers of the pectoralis major contribute more to adduction and extension from a flexed position rather than initiating flexion.

So the combination of upper fibers of pectoralis major, anterior deltoid, and biceps brachii best represents the agonists for shoulder flexion.