Pain when rotating the arm is mostly caused by trauma, muscle fatigue or strain, and epicondylitis of the humerus. 1. Traumatic injury: due to a history of trauma, muscle strain, sprain, or even bone or joint capsule injury, the symptoms of arm rotation pain will occur. 2. Muscle fatigue or strain: muscle fatigue after a long period of arm exercise, which in turn leads to symptoms of muscle tension, or long-term muscle strain, which can also cause pain manifestations. 3. Epicondylitis of the humerus: commonly known as “tennis elbow”. Mostly due to long-term chronic strain produced tendon local inflammation, and then stimulate the muscles to produce pain. There are many reasons for this symptom, it is recommended that after the symptoms appear, timely medical treatment under the guidance of a professional physician to carry out targeted treatment.