The rotator cuff includes the supraspinatus, infraspinatus, subscapularis, and teres minor, which can increase the stability of the humeral head in the glenoid. Tears and inflammation of these tendons often occur in repetitive sports that require extreme abduction of the shoulder joint (such as baseball, freestyle, backstroke and butterfly stroke, weightlifting, and racket sports). When the upper limb is extended, the humeral head hits the acromion and coracoacromial ligament forward, causing supraspinatus tendon injury. Chronic irritation can cause subacromial bursitis, aseptic inflammation, and tendon erosion. Acute and huge violence can cause rupture of the rotator cuff. If you continue to train despite the pain, it will cause periostitis of the supraspinatus tendon insertion or even tendon avulsion.