Which of the following muscles acts as an internal rotator of the shoulder joint?

The pectoralis major is recognized as a powerful internal rotator of the shoulder joint. This muscle originates from the clavicle, sternum, and the cartilage of the true ribs, inserting on the humerus. When it contracts, it brings the arm closer to the body while also rotating the shoulder joint internally. This internal rotation is critical in many upper body movements, especially in activities that require bringing the arms across the body.

In contrast, the other muscles listed have different roles in shoulder joint movements. The infraspinatus and teres minor are primarily external rotators, working to rotate the arm away from the body. The posterior deltoid also contributes to shoulder extension and external rotation. Understanding the functions of these muscles is essential for proper training and rehabilitation in pilates and other movement practices.