The rotator cuff—a group of four small but mighty muscles: supraspinatus, infraspinatus, teres minor, and subscapularis—acts as the shoulder’s dynamic stabilizer. These muscles keep the humeral head centred in the glenoid fossa during movement, and they work constantly, even when we’re doing something as simple as reaching for a cup of tea. They control rotation, guide elevation, and prevent the shoulder from collapsing into the kind of sloppy mechanics that lead to impingement and pain.