There are many reasons for shoulder pain when holding the arm up, and the common ones are frozen shoulder, myofasciitis, trauma and so on. 1. Frozen shoulder: chronic specific inflammatory reaction caused by various reasons, with self-limitation, initially manifested as shoulder pain, mostly paroxysmal, shoulder pain can occur when shoulder exertion, such as arm support, and can spread to the neck and upper limbs, accompanied by symptoms of shoulder joint activity limitation. 2. Myofasciitis: non-specific inflammatory changes occur in shoulder muscles and fascia due to trauma, strain injury, etc. Abnormally sensitive nodules can be detected in muscle fibers, which may cause shoulder muscle pain if the trigger point is stimulated when the arm is held up against the body. 3. Trauma: If there is a tendon tear around the shoulder joint, shoulder pain may occur when the damaged muscle is involved when the arm is propped up against the body. There may be other reasons for shoulder pain, such as shoulder impingement syndrome. It is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and give targeted treatment under the guidance of the doctor.