Strengthening the infraspinatus and teres minor muscles would most improve which shoulder movement when resisted?

• A. Internal rotation
• B. Abduction
• C. Lateral (external) rotation
• D. Flexion

Answer: (C)

The key idea is that the infraspinatus and teres minor are external rotators of the shoulder. They attach to the posterior aspect of the shoulder and to the greater tubercle of the humerus, and their primary job is to rotate the arm outward (away from the body) at the glenohumeral joint while helping stabilize the head of the humerus in the socket.

When you strengthen these muscles, you improve the ability to resist a force that tries to rotate the arm externally. So resisted lateral (external) rotation becomes more powerful and controlled. Other shoulder movements rely on different muscle groups—internal rotation mainly comes from the subscapularis, abduction from the supraspinatus and deltoid, and flexion from the anterior deltoid and other flexors—so strengthening the infraspinatus and teres minor specifically enhances external rotation the most.