Which muscles act as primary agonists for lateral rotation of the shoulder?

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

Answer: (C)

External rotation of the shoulder is produced mainly by the rotator cuff muscles that wrap around the humeral head. The two primary external rotators are the infraspinatus and the teres minor. The posterior fibers of the deltoid can contribute to external rotation, especially when the arm is elevated, but they’re not the main drivers. Other muscles listed act predominantly as internal rotators or have primary roles other than external rotation (for example, some initiate abduction or internal rotation). So the combination that includes the two primary external rotators plus the posterior deltoid best accounts for lateral rotation of the shoulder.