Which muscle is responsible for external rotation of the humerus?

The teres minor is indeed responsible for external rotation of the humerus. It is one of the four rotator cuff muscles, which play a crucial role in stabilizing and moving the shoulder joint. The teres minor, located on the posterior aspect of the shoulder, assists in externally rotating the arm by pulling the humeral head backward and upward. This action is essential for many upper body movements and contributes to the overall stability and function of the shoulder.

In contrast, the subscapularis is responsible for internal rotation of the humerus, while the supraspinatus primarily aids in abduction of the arm. The pectoralis major, although it has some role in arm movement, is more involved in flexion, adduction, and internal rotation rather than external rotation. Understanding the specific functions of these muscles highlights the importance of the teres minor in facilitating external rotation of the shoulder joint.