Evaporation of sweat is another way we lose heat through the skin, especially during exercise. But when the humidity is high, evaporation is reduced. Moisture stays on our skin, making us feel hot and sticky. Hot and humid weather is tough on the body. Exercise makes things worse.
Exercise increases metabolism.
A brisk walk can increase metabolism fourfold, which means the body must lose heat four times more rapidly to keep body temperature from rising. And when doing vigorous exercise, like jogging, metabolism can increase tenfold or more. Fortunately, when you repeatedly expose your body to exercising in the heat, you adapt and become better able to cope. But in the spring, before your body has had the opportunity to adapt, you might find yourself confronting rough conditions that you underestimate. Therefore, you'd better respect the heat and not push yourself as hard as you might in cooler weather.