This situation is mainly a problem of the way of exercise, generally do anaerobic exercise is more likely to increase muscle, so that this situation may be in the process of running too fast or too short, in this case will instead increase muscle. If it is endurance exercise, that is, aerobic exercise, it can help burn fat, and muscle increase will not be particularly obvious, usually exercise recommended more than half an hour of time, should be able to improve such a situation. Warm up before running and stretch after running.