Infraspinatus is a triangular muscle located at the back of the shoulder. It is one of the four muscles of the rotator cuff and helps the upper arm rotate outward. Related Definitions Rotator Cuff Rotator Cuff Tear Subscapularis Supraspinatus Teres Minor Editor’s Top Picks Rotator Cuff Injuries How Do Rotator Cuff Injuries Occur? Rotator Cuff Injuries: Symptoms Rotator Cuff Injuries: Initial Treatment Rotator Cuff Injuries: Diagnosis Rotator Cuff Tear Surgery