North by Northwest

So says Gina Kolata of the New York Times.

“The big question was, ‘Is it ever too cold?’” Dr. Castellani said. “The answer is no. People go to the poles, people are out there when it’s minus-50 degrees, people do incredible things, and safely. There really isn’t a point where you can tell people it is not safe anymore.”

Dr. Timothy Noakes, an exercise physiologist at the University of Cape Town in South Africa who was a reviewer of that position paper, even supervised a swimmer, Lewis Gordon Pugh, who swam 1 km or (.62 miles) in 19 minutes at the North Pole last July, in water that was between 29 and 32 degrees.

The problem with exercising in the cold, exercise physiologists say, is that people may be hobbled by myths that lead them to overdress or to stop moving, risky things to do.

Some worry that cold air will injure their lungs or elicit asthma symptoms. Or they are convinced that they are more susceptible to injury when it is cold and that they have to move more slowly — forget about sprinting or running at a fast clip.

But lungs are not damaged by cold, said Kenneth W. Rundell, the director of respiratory research and the human physiology laboratory at Marywood University in Scranton, Pa. No matter how cold the air is, by the time it reaches your lungs, it is body temperature, he explained.

Some people complain that they get exercise-induced asthma from the cold. But that sort of irritation of the respiratory tract is caused by dryness, not cold, Dr. Rundell said. “Cold air just happens not to hold much water and is quite dry,” he said. You’d have the same effect exercising in air that was equally dry but warm.

Dr. Rundell and Tina Evans, a Ph.D. candidate, showed this a few years ago in a study designed to dispel what Dr. Rundell called the myth that cold air can induce asthma. Volunteers with exercise-induced asthma, whose airways tended to narrow after exercise in the cold, breathed cold air or room temperature air that was equally dry. Their airways narrowed in response to the dryness of the air, not its temperature, Dr. Rundell said.

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Another myth is that you have to acclimatize to cold, just as you do to heat. It’s true that peoples’ bodies adapt to hot weather and that adaptation makes people feel better when they exercise in the heat. It also improves performance. With heat adaptation, you sweat more profusely, your sweat is less salty and your blood volume increases.

But exercise physiologists find only modest adaptation to cold. The body’s main responses to cold — constricting blood vessels near the skin, shunting blood to the body’s core and shivering — do not improve if you spend more time in the cold. Nor are the physically fit any better at adaptation than the sedentary.