Which muscle inserts on the lesser tubercle of the humerus?

The muscle that inserts on the lesser tubercle of the humerus is the subscapularis. This muscle plays a critical role in the functioning of the shoulder joint, as it is part of the rotator cuff group. The subscapularis is primarily responsible for the internal rotation of the humerus and stabilization of the shoulder joint. Its positioning allows it to effectively engage with the lesser tubercle, which is located on the anterior aspect of the humerus, providing leverage for its action.

In contrast, the other muscles listed are responsible for actions involving the greater tubercle and perform different functions. The infraspinatus and teres minor are involved in external rotation and lateral stabilization of the shoulder, inserting on the greater tubercle, while the supraspinatus assists in the abduction of the arm and also attaches to the greater tubercle. Understanding the specific insertions and functions of these muscles is critical for comprehending shoulder mechanics and addressing any related injuries or conditions.