When the human body is exercising, the blood circulation is accelerated and strengthened, and the blood supply of local tissues is sufficient, especially skeletal muscle. When exercising, the blood increases sharply, and the muscle fibers at this time are also thickened due to the increase of local blood supply. The continuous contraction of skeletal muscle causes most of the blood in the body to flow here for the contraction of skeletal muscle, which is the redistribution of blood during human exercise. When the human body changes from exercise to rest, that is, when it is at rest, because the skeletal muscle does not exercise at this time, that is, the contraction only maintains the general daily needs, the blood will be redistributed, distributed evenly, and will not gather locally, which is why the arm becomes thicker during exercise and recovers during rest.