The subscapularis muscle is a large, triangular muscle located in the anterior (front) region of the shoulder. It originates at the medial border of the scapula (shoulder blade), and inserts into the lesser tubercle of the humerus (upper arm bone). The subscapularis muscle is one of the muscles that make up the rotator cuff, and is located deep to the serratus anterior muscle.

The main function of the subscapularis muscle is to medially rotate (rotate inward) the arm at the shoulder joint. This movement is essential for activities such as bringing the arm across the body, and helps to provide stability and support for the shoulder joint. The subscapularis muscle also helps to stabilize the shoulder joint, and assist in adduction (movement towards the midline) of the arm.

In everyday life, the subscapularis muscle is used in many activities that involve medially rotation of the arm, such as reaching into a pocket or brushing the hair. It is also used in activities that require stability and support for the shoulder joint, such as carrying a heavy bag or pushing a door open.