The rotator cuff muscles are a group of muscles that make up the major muscles that rotate the arm and stabilize the shoulder joint. There are four muscles that make up the group: supraspinatus muscle, infraspinatus muscle, teres minor muscle and the subscapularis muscle. Injury to the rotator cuff muscles are very common with 9.7% in people 20 years old or younger, and 62% in people over the age of 80.
The subscapularis muscle is the largest of the rotator cuff muscles and originates from underside of the scapula (shoulder blade). The muscle inserts into the proximal (top) humerus bone but at a different site than the other rotator cuff muscles. It is innervated by the upper and lower subscapular nerve which stems from the cervical 5th through 7th nerve roots. Its main action is to internally rotate the arm, and is the only muscle of the rotator cuff muscles to perform this action (but not the only muscle in the body).
The subscapularis muscle is less likely than the other rotator cuff muscles to be injured. It is typically injured in repetitive overhead activity. Athletes with overhead throwing or tennis players are at a higher risk of injury. Tears, tendonitis (inflammation), and impingement are the most common causes of injury.
Stretches for the subscapularis include sleeper stretches (external rotation) and using a pole to externally rotate the arm. To strengthen the subscapularis muscles, exercises such as internal rotation of the arm, at 90 degrees or by the side, with a band or dumbbells will help. When trying to rehabilitate an injured rotator cuff muscle, starting with restoring normal range of motion and strengthening the “scapular stabilizers” is always an important starting point. All these exercises should be done with the guidance of your health care provider to progress in a safe way.
Aguirre K, Mudreac A, Kiel J. Anatomy, Shoulder and Upper Limb, Subscapularis Muscle. [Updated 2020 Aug 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513344/