I did a search, and didn't see this posted. It's an article from the NY Times basically saying that science has showed you can exercise without danger no matter how cold it is outside.
Too Cold to Exercise? Try Another Excuse
By GINA KOLATA, The New York Times
JULIA HENSLEY, a 41-year-old artist, got a taste of bitter cold a decade ago when she spent a winter living on a glacier near Seward, Alaska. Typical winter temperatures were 10 to 15 degrees below.
“The first time it got really cold, I was scared of it,” Ms. Hensley said. “My instinct was to get a stack of books and curl up beside the wood stove.”
But a boyfriend persuaded her to go out anyway, to cross-country ski or snowshoe for hours in deep snow. He taught her, she said, that as long as she kept moving, she would be fine.
It was a conclusion — that extreme cold can be safe for exercisers — that runs contrary to conventional wisdom. But in fact, said John W. Castellani, an exercise physiologist at the Army Research Institute of Environmental Medicine, it turns out that even though cold can be frightening, more people are injured exercising in the heat than exercising in the cold.
Dr. Castellani was lead author of a 2006 position paper from the American College of Sports Medicine on exercising in the cold.
“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.
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