COOLING DOWN AFTER EXERCISING

Report #7064; 3/16/97

Slow down gradually after exercising vigorously. Cooling down prevents feeling faint and passing out.

When you sit or stand, your heart's major task is to raise blood from your feet. When you exercise, your heart's main function is to pump blood to your exercising muscles. If it had to do the extra work of raising blood from your feet, it would pump so little blood to your muscles that you would tire with the mildest exercise. Therefore, you heart has to depend on your leg muscles to raise blood against gravity. When your leg muscles relax, the veins near them fill up with blood. When they contract, they squeeze the veins near them and pump blood up toward your heart. Alternately contracting and relaxing leg muscles pumps extra blood through your body. When you stop suddenly after exercising vigorously, your leg muscles stop pumping and your heart has to pick up the extra work. To make your heart beat faster and stronger, your body increases production of its own natural stimulants called adrenalin and noradrenaline. This can cause the heart to beat irregularly, depriving your brain of adequate oxygen, so you feel dizzy and can even pass out. People with heart disease can develop irregular heart beats.

Cooling down does not prevent muscle soreness. It increases circulation and helps to clear lactic acid from your muscles at a faster rate, but muscle soreness after exercise has nothing to do with lactic acid accumulation. It is due to muscle damage caused by exercise. So, you cool down to prevent dizziness, not muscle soreness.

By Gabe Mirkin, M.D., for CBS Radio News