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.
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.
People with this problem should see a respiratory specialist and take medication when they exercise in dry air, Dr. Rundell said. And, he added, “you might want to use a balaclava,” so your exhaled breath can moisten the air you breathe.
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 andshivering — do not improve if you spend more time in the cold. Nor are the physically fit any better at adaptation than the sedentary.
“Right now, we’re not sure if there is any degree of habituation,” said Robert Kenefick, a research physiologist at the Army Research Institute of Environmental Medicine.
Dr. Noakes said that during Mr. Pugh’s North Pole swim, hypothermia was a real concern. Hypothermia can happen suddenly in icy water, with the swimmer’s core temperature plummeting, and the fear was that Mr. Pugh might pass out and sink before he could be rescued. Mr. Pugh, an experienced cold-water swimmer, was wearing a device to monitor his temperature, but nonetheless, Dr. Noakes was “petrified,” he said.
The biggest risk of hypothermia comes with a combination of wet and cold. That is because water transfers heat from the body 70 times more efficiently than air.
Hypothermia begins to set in when the body’s core temperature falls to 95 degrees. That elicits shivering and a rise in blood pressure. But if your temperature drops to 85, you lose consciousness, and if it goes much lower, you can die. The trick to avoiding hypothermia is to keep moving, Dr. Noakes said. “As long as you keep moving you are not going to die because you generate so much heat.”
One mistake winter exercisers make is wearing too much clothing. You don’t want to sweat profusely because you overdressed.
“You should feel cool before you start exercising,” Dr. Castellani said. “You should not feel comfortable.”
That means, Dr. Noakes said, that even in temperatures as low as 10 to minus-20 degrees, a runner probably needs to wear no more than a track suit, mittens or gloves and a hat.
The other major concern, frostbite, can come on fast, as my running partner Jennifer Davis, 37, discovered about a decade ago. It starts when the skin’s temperature drops to 82 degrees and you feel an area of skin is becoming really cold. At a skin temperature of 68 degrees, the skin starts to hurt. It may tingle or burn or ache or you may feel a sharp pain. When the skin’s temperature falls to 50 degrees, it feels numb. And when the skin’s temperature reaches 27 degrees, the skin freezes. The result is frostbite.
Ms. Davis got frostbite when she went out for a run early in the morning on a cold, windy day with temperatures in the teens. She ran for about an hour wearing a baseball cap. Her ears hurt for a while, then the pain went away.
She took off a glove to touch her ears so she could find out just how cold they were. To her shock, one of her ears cracked. “It was sort of like semi-frozen meat,” she recalled.
When she got home, she was horrified by her red and swollen ear. An ear, nose and throat specialist diagnosed frostbite and told her that her ear would be sensitive to the cold for the rest of her life.
He was wrong, though. The ear was red and stuck out for weeks, but it healed. Now, Ms. Davis said, she can’t even remember whether it was her right or left ear. But ever since, she has worn a hat that covers her ears when she runs in the cold.
As for Ms. Hensley, the woman who lived in Alaska one winter, she now lives in Seattle and rides her bike in the winter rain, charging up hills.
“I just remember the lesson I learned that winter,” she said. “You don’t have to stand inside and say, ‘Oh, it’s a yucky day.’ You can go out in anything. You just have to do it.”