The pain in the arm after the workout when stretched out may be the exercise process may be the injury to the muscles, ligaments, or excessive exercise during the exercise process, resulting in an increase in local lactic acid. You can massage or apply heat to the arm, which in turn can relieve muscle soreness. At the same time, pay attention to rest, it is recommended that you must develop a reasonable and moderate exercise plan, reduce the amount of exercise, gradual, and can be fully prepared before each exercise to avoid ligament and muscle strains. If long-term pain, you need to go to the hospital for further treatment.