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Alex Hutchinson draws on the latest research to answer your fitness and workout questions in this biweekly column on the science of sport

The question

Will I freeze my lungs by exercising outside in the cold?

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The answer

The strangest story that Michel Ducharme, a scientist with Defence Research and Development Canada, has encountered is the Nordic skiers who were swallowing Vaseline to coat their airways as a protective measure against cold air.

"That's just crazy," he says - and entirely unnecessary.

Dr. Ducharme is the researcher whose work led to a major revision of the wind-chill scale earlier this decade, thanks to the efforts of volunteers who sat in a frigid wind tunnel until their faces developed frost nip. And he's happy to dismiss the idea that your lungs will suffer from contact with cold air. "The heat exchange is very quick," he says, "and there's no evidence of any risk of freezing tissue."

This may be cold comfort for people who swear they are overcome by coughing fits or throat pain when they exert themselves in subzero conditions. Indeed, cold air has long been implicated in exercise-induced bronchoconstriction, an asthma-like narrowing of the airways that leads to shortness of breath and coughing. EIB affects between 4 and 20 per cent of the population.

In these cases, though, it's the dryness of the air, not its temperature, that triggers the response, says John Brannan, a researcher at McMaster University's Firestone Institute for Respiratory Health in Hamilton. The cells that line our airways are highly sensitive to dehydration, and breathing hard during exercise greatly increases the amount of dry air rushing past these cells.

Although this hypothesis has been disputed for many years, recent experiments by Kenneth Rundell, a researcher at Marywood University in Scranton, Penn., who spent 10 years as an exercise physiologist with the United States Olympic Committee, have shown that warm, dry air and cold, dry air trigger identical responses.

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There are some makeshift solutions: Wearing a scarf or balaclava over the mouth can moisten the air as it is inhaled. "That makes breathing more difficult," Dr. Rundell notes, so it's less useful for skiers or runners in competition, but may be fine in training. Commercial heat-exchange masks, which accomplish the same thing with less breathing resistance, are also available.

If the EIB symptoms are serious - and confirmed by a lung-function test administered by a doctor - asthma medication can help alleviate the symptoms. Contrary to what some athletes and coaches believe, though, there's no performance benefit to taking these medications if you don't suffer from EIB, Dr. Rundell says.

It's still not clear whether chronic intense exercise can lead to EIB. Winter Olympic athletes have a higher prevalence than the general population does, but so do summer athletes, who breathe in more pollution and allergens. This is a more controversial topic and only relevant to those training at elite levels.

For most people, it's safe to conclude that, short of an asthma attack, exercising outside in the dead of winter is perfectly safe.

Some people do experience a burning sensation in their throat or upper airways when they exercise in the cold, Dr. Rundell says, "but that's just a response of the nerve endings."

In other words, you're not freezing your lungs - so you might as well keep going.

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Alex Hutchinson is a former member of Canada's long-distance running team, and has a PhD in physics.

*****

Cold facts about breathing

No matter how cold and dry the outside air is, it will be at body temperature and near 100-per-cent relative humidity by the time it reaches the alveoli in the lungs, says physiologist Kenneth Rundell.

That means it's picking up moisture as it passes through the airways - and that can dry those surfaces out,

triggering an inflammatory response that narrows the airways and makes it harder to breathe.

This "exercise-induced bronchoconstriction" affects between 4 and 20 per cent of the population.

When the airways are irritated, they become blocked by tissue inflammation (enlarged vessels and muscle cells), increased mucus production, and the muscles of the bronchial wall contracting, all of which cause a shortness of breath.

TRISH McALASTER / THE GLOBE AND MAIL

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