Which action does the teres minor primarily assist with?

The teres minor primarily assists with shoulder external rotation. This muscle is part of the rotator cuff and is located on the back of the shoulder. Its fibers run from the lateral border of the scapula to the greater tubercle of the humerus, which places it in a position that effectively allows it to pull on the humerus to facilitate external rotation.

When the arm is in a position of external rotation, the teres minor works alongside other muscles, specifically the infraspinatus, to rotate the humeral head outward and away from the body. This action is crucial for various activities, such as throwing or reaching overhead, where external rotation is needed to position the arm correctly.

In contrast, shoulder flexion, internal rotation, and adduction involve different muscle groups. Flexion primarily involves the anterior deltoid and pectoralis major; internal rotation is performed mainly by the subscapularis and pectoralis major; and adduction requires muscles like the latissimus dorsi and teres major. Understanding the specific role of the teres minor helps clarify its importance in shoulder mechanics and stability.