Everybody should have experienced the fast beating pulse after exercise. The rapid pulse indicates that the heat is produced in the body. However, the most of the heat produced by the extreme exercise is unnecessary for the body, and it takes a lot of energy to diffuse it. This is the reason why exercising too much becomes burdensome.
It is ideal for those who always exercise like athletes not to produce heat much even during exercise, so the normal pulse of an athlete tends to be rather slow.
*This article is translated from "Yamai hitokuchi Memo" written by Shoji Kobayashi, 2005.