COVER YOUR FACE
The challenge: Going bareheaded in the winter is like leaving the lid off your thermos. Classic studies in the 1950s showed that if you wear winter clothes but no hat at 4 C, you lose about 50 per cent of your body heat through your head.
The research: A U.S. Army study published in early 2011 showed that your face is almost as important as the top of your head for heat loss. Volunteers spent an hour in a cold chamber with a wind chill of -20 C; those who wore a balaclava had measurably warmer fingers and toes than those wearing a normal hat. Your body tries valiantly to keep your brain warm by shunting blood away from your extremities toward your head.
The takeaway: Good mittens and socks are a must – but if your fingers and toes still get cold, be sure to break out your hat and scarf.
The challenge: Staying warm becomes much harder if you get wet. In fact, water's greater thermal capacity means that it can transmit heat by convection 70 times more quickly than air.
The research: Modern high-tech workout clothing wicks and breathes and performs lots of other neat tricks. But a 2008 European Union study of six different types of clothing confirmed that the basic laws of physics still apply: Once your clothes get wet, you'll be losing about twice as much heat as when they were dry.
The takeaway: The key is to avoid sweating in the first place. For a moderately vigorous activity such as running, cross-country skiing or snowshoeing, dress so that you feel unpleasantly cold for the first five minutes. As you warm up, remove layers before you start sweating.
GET USED TO IT?
The challenge: The first blasts of winter are the worst. After a few months, sub-zero temperatures don't feel quite as shocking – but does that mean your body has adapted to maintain a higher temperature?
The research: A recent study by Brock University's Stephen Cheung and his collaborators had volunteers dip their hands and feet in 8 C water for 30 minutes a day. After 15 days, their average pain score on a scale of 1 to 10 had dropped from 4.5 to 2.5 – a clear sign of acclimatization. But those subjective changes weren't accompanied by better circulation or higher skin temperature in their cold hands.
The takeaway: After a long winter, your extremities will be just as cold, but you won't notice it as much – a potentially dangerous combination for frostbite. Don't get cocky about your apparent resistance to cold.
BEAT WIND CHILL
The challenge: Wind doesn't actually make the air colder; it just blows away the micro-layer of warm air around your body, making you feel colder and accelerating convective heat loss.
The research: Understanding wind chill is important for comfort, but it's crucial for avoiding frostbite. Researchers at Defence Research and Development Canada played a key role in developing revised international wind chill guidelines a decade ago. They found that the key threshold for frostbite risk is when the wind chill drops below -27 C, at which point exposed skin can develop frostbite in less than 30 minutes.
The takeaway: When the wind is vicious, make sure to cover bare skin – and remember that the wind chill you'll experience is even colder during high-speed activities such as running and skiing.
The challenge: It's the classic excuse for staying indoors, but there is actually no risk that you'll freeze your lungs by breathing deeply in cold air. Still, some people do report coughing or shortness of breath during winter exercise.
The research: A 2005 study by Kenneth Rundell at Marywood University in Pennsylvania finally settled this long-standing debate. The "exercise-induced bronchoconstriction" (or EIB) endured by between 4 and 20 per cent of winter athletes is caused by the dryness of winter air, not its temperature. Breathing large volumes of dry air can irritate the sensitive cells lining your airways, causing them to constrict.
The takeaway: If you suffer from EIB, cover or partly cover your mouth with a thin balaclava, a scarf or a breathing mask. That will trap water vapour from your exhaled breath, moistening the air you're about to inhale.
Alex Hutchinson blogs about research on exercise at sweatscience.com . His new book – Which Comes First, Cardio or Weights? – is now available.