By GINA KOLATA


The importance of cooling down after exercise is enshrined in training lore. It’s in physiology textbooks, personal trainers often insist on it, fitness magazines tell you that you must do it - and some exercise equipment at gyms automatically includes it. You punch in the time you want to work out on the machine, and when your time is up, the machine automatically reduces the workload and continues for five minutes so you can cool down.

The problem, says Hirofumi Tanaka, an exercise physiologist at the University of Texas, Austin, is that there is no science behind the advice. The cool-down “is an understudied topic,” he said. “Everyone thinks it’s an established fact, so they don’t study it.”

It’s not even clear what a cool-down is supposed to be. Some say you just have to keep moving for a few minutes. Others say you have to spend 5 to 10 minutes doing the same exercise, only slowly. Still others say a cool-down should include stretching.

And it’s not clear what the cooldown is supposed to do. Some say it alleviates muscle soreness. Others say it prevents muscle tightness or relieves strain on the heart.

Exercise researchers say there is only one agreed-on fact about the possible risk of suddenly stopping intense exercise. When you exercise hard, the blood vessels in your legs are expanded to send more blood to your legs and feet. And your heart is pumping fast. If you suddenly stop, your heart slows down, your blood is pooled in your legs and feet, and you can feel dizzy, even pass out.

The best athletes are most vulnerable, said Dr. Paul Thompson, a cardiologist and marathon runner who is an exercise researcher at Hartford Hospital in Connecticut. “If you are well trained, your heart rate is slow already, and it slows down even faster with exercise,” he said.

That effect can also be deleterious for someone with heart disease, said Carl Foster, an exercise physiologist at the University of Wisconsin-La Crosse, because blood vessels leading to the heart are already narrowed, making it hard for blood to get in.

But does it matter for the ordinary, average athlete? “Probably not a great deal,” Dr. Thompson said. And, anyway, most people don’t just stand there, stock still, when their workout is over. They walk to the locker room or to their house or car, getting the cool-down benefit without officially “cooling down.”

The idea of the cool-down seems to have originated with a popular theory - now known to be wrong - that muscles become sore after exercise because they accumulate lactic acid. In fact, lactic acid is a fuel. It’s a normal part of exercise, and it has nothing to do with muscle soreness. But the lactic acid theory led to the notion that by slowly reducing the intensity of your workout you could give lactic acid a chance to dissipate.

In fact, Dr. Tanaka said, one study of cyclists concluded that because lactic acid is good, it is better not to cool down after intense exercise. Lactic acid was turned back into glycogen, a muscle fuel, when cyclists simply stopped. When they cooled down, it was wasted, used up to fuel their muscles.

As far as muscle soreness goes, cooling down doesn’t alleviate it, Dr. Tanaka said.

And muscle tightness?

“There are no data to support the idea that a cool-down helps,” Dr. Foster said.

Dr. Thompson says if he is doing a hard track workout he will jog for a short distance when he finishes to avoid dizziness.

As for Dr. Tanaka, he does not cool down at all. He sees no particular reason to do anything after exercising other than just stop.


EVAN SUNG FOR THE NEW YORK TIMES / Walking to the locker room, car or house may be a sufficient cooldown for most exercisers.