Because exercise helps use up oxygen, it causes your body to burn stored fat and helps you maintain a normal weight. For instance, if you walk 4 miles a day four times a week, you can burn about 1,600 calories or nearly half a pound a week. If you don't change your diet at all and keep walking the same distance over six months, you'll lose 12 pounds. Walk the same distance for a year and you'll drop 24 pounds.
The skin also serves as a release point for heat. (See “Why Does My Face Turn Red When I Exercise?” for more on that.) When you exercise, your muscles generate a lot of heat, which you have to give up to the environment so your body temperature doesn’t get too high, Hackney says. The heat in the muscle transfers to the blood, which shuttles it to the skin; it can then escape into the atmosphere.