Which muscles act as the agonists for horizontal adduction of the shoulder?

• A. Pectoralis Major, Deltoid (Anterior)
• B. Deltoid (Posterior), Latissimus Dorsi
• C. Subscapularis, Teres Major
• D. Serratus Anterior, Pectoralis Minor

Answer: (A)

For horizontal adduction of the shoulder, the arm is moved across the chest toward the midline, typically with the shoulder flexed around 90 degrees. The primary movers in this motion are the pectoralis major and the anterior part of the deltoid. The pectoralis major pulls the humerus medially across the chest, crossing the midline, while the anterior deltoid assists by contributing to shoulder flexion and helping drive the arm across the body when the arm is already flexed. Together, these two muscles provide the main force needed for this horizontal crossing.

The other muscles listed don’t serve as the main effectors for this specific motion. The posterior deltoid mainly facilitates horizontal abduction. Latissimus dorsi and teres major are strong adductors and internal rotators, but they don’t act as primary horizontal adductors when the arm is in the horizontal plane across the chest. Subscapularis primarily follows internal rotation and stabilization, and serratus anterior with pectoralis minor mainly stabilize the scapula rather than drive the humerus across the chest.