Arc of pain is a chronic shoulder pain syndrome caused by repeated friction and impingement between the structures in the subacromial space and the rostral shoulder arch during shoulder abduction activities. The common clinical feature is a painful arc during active abduction of the shoulder joint, while the pain is significantly reduced or even completely absent during passive activities. So, how is the pain arc syndrome caused? The following is an introduction to the causes of the pain arc sign: a variety of shoulder disorders can cause it. For example, supraspinatus rupture, supraspinatus tendinitis, supraspinatus calcification, subacromial bursitis, and humerus greater tuberosity fracture can be caused. The main symptom of this disease is pain in the shoulder, mainly around the acromion, sometimes involving the entire deltoid muscle, and the pain is worse at night. When the upper arm is abducted by 60° to 80°, there is obvious pain, and sometimes the shoulder joint can feel stuck by “something” and cannot be lifted. During the treatment period, shoulder impingement, such as lifting heavy objects, should be avoided. In the later stages of treatment, active functional exercises should be carried out, especially for those with limited range of motion of the shoulder joint. In particular, for those who have limited range of motion of the shoulder joint, you can practice back and forth, shaking the shoulder, swinging the shoulder, etc. The range and amplitude can be from small to large. The exercises can loosen the adhesions and contractures of the soft tissues of the shoulder and prevent the occurrence of frozen shoulder.