Muscle pain in the shoulder may be caused by the following reasons: 1. The patient may have been engaged in physical labor for a long time, resulting in strain on the shoulder muscles and pain. 2. The patient may have suffered a trauma to the shoulder or a strain after strenuous exercise, which may cause damage to the soft tissue and muscle pain. 3. 4.It may be that the patient’s shoulder is inflamed, such as frozen shoulder, ligamentitis or ligament strain, resulting in muscle inflammation, swelling and pain. 5.It may be that the patient suffers from cervical spondylosis, resulting in nerve compression at the shoulder, which makes the muscle unable to receive nerve signals, resulting in pain. When this phenomenon occurs, it is recommended that the patient immediately go to the hospital for examination and cooperate with the doctor for treatment in order to get rid of the pain as soon as possible.