What is one of the primary actions of the subscapularis?

The subscapularis is one of the four rotator cuff muscles and is primarily responsible for shoulder medial rotation. This muscle is located on the anterior (front) surface of the scapula and inserts onto the lesser tubercle of the humerus. When it contracts, it pulls the humerus inward towards the body, resulting in the inward or medial rotation of the shoulder joint. This action is crucial in various movements, such as reaching across the body or during certain throwing activities, making it an essential component in shoulder stability and function.

Understanding this function of the subscapularis also highlights its role in maintaining proper shoulder mechanics and preventing dislocations, especially during activities that demand a lot of shoulder movement. The other options, while related to shoulder movement, describe actions that the subscapularis does not perform: abduction and lateral rotation are facilitated by other muscles, while shoulder extension is primarily the role of muscles such as the latissimus dorsi and teres major.