There are two reasons for legs thickening after running. One is that when running, local blood circulation is accelerated, and protein synthesis reaches its peak at the end of running, which accelerates protein synthesis and promotes the repair of damaged muscles and the generation of new muscles, so that the muscle fibers of the legs are thickened and the muscles are increased, which leads to thickening of the legs. Secondly, the movement before and after the movement did not do a good job of fully stretching the muscles. To reduce the phenomenon of running to make the legs thicker, before and after the movement to do a good job of fully stretching the muscles of the movement, after the movement to eat less food containing high protein, reduce protein synthesis, thereby reducing the generation of muscle.