okay, you want the body temperature kept at an even level, don't have it too high, don't have it too low, cos if you shiver you make use of muscles and then the muscles will call on oxygen and then you'll shiver, you don't want them there you want the blood in here, if you make them sweat you'll bring the blood to the surface of the skin again to lose heat, and that's again precisely where you don't need, you want it in the core of the body so you maintain an even body temperature.