Which muscles contribute to shoulder external rotation?

Which muscles contribute to shoulder external rotation?

• A. Infraspinatus and teres minor, with assistance from posterior deltoid.
• B. Infraspinatus and teres minor.
• C. Infraspinatus alone.
• D. Teres minor and deltoid.

Answer: (A)

External rotation of the shoulder is mainly produced by the rotator cuff muscles, with two primary contributors doing the heavy lifting: the infraspinatus and the teres minor. These two attach to the greater tubercle of the humerus and pull the humeral head laterally to rotate the arm outward while also helping to stabilize the joint during movement. The posterior deltoid can contribute as a synergist, especially in positions that allow its fibers to assist the rotation, such as when the arm is abducted or moving through resisted external rotation. That combination—two primary rotators plus the assisting posterior deltoid—best explains how external rotation is generated and controlled. Options that omit one of the primary rotators or rely on the deltoid alone don’t capture the main mechanism, since the deltoid is more involved in other shoulder movements and only supports external rotation rather than performing it as effectively.

External rotation of the shoulder is mainly produced by the rotator cuff muscles, with two primary contributors doing the heavy lifting: the infraspinatus and the teres minor. These two attach to the greater tubercle of the humerus and pull the humeral head laterally to rotate the arm outward while also helping to stabilize the joint during movement. The posterior deltoid can contribute as a synergist, especially in positions that allow its fibers to assist the rotation, such as when the arm is abducted or moving through resisted external rotation. That combination—two primary rotators plus the assisting posterior deltoid—best explains how external rotation is generated and controlled. Options that omit one of the primary rotators or rely on the deltoid alone don’t capture the main mechanism, since the deltoid is more involved in other shoulder movements and only supports external rotation rather than performing it as effectively.