Swimming arm pain may be caused by lactic acid buildup due to strenuous activities or muscle strain or fasciitis. 1. Lactic acid accumulation: Swimming is a high-intensity muscle movement, if the patient did not warm up sufficiently before swimming, or swimming time is too long, the amount of exercise, will lead to a large number of muscle lactic acid lactic acid caused by the accumulation of lactic acid, resulting in arm pain. 2. Muscle strain: if the patient did not warm up, swimming movement is not coordinated, arm force too fast and too fierce or swimming time is too long, will lead to arm muscle strain, resulting in pain. 3. Fasciitis: If the patient swims frequently and for a long time, it is easy to cause inflammation of the soft tissues of the arm, such as fascia, ligament, etc. due to low water temperature, long time load and other stimuli. Thus causing pain. If the patient appears after swimming arm pain and can not be relieved, should promptly go to the hospital to receive appropriate treatment.