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- Alex Hutchinson (@sweatscience)
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My Jockology column in today’s Globe and Mail gets seasonal and looks at five bits of research related to exercising outdoors in the winter. For example:
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.
Read the whole column here.
Great article Alex. I know a few people with EIB so will pass along the tip about wearing the balaclava to trap moisture although I personally find it unpleasant to run with a wet piece of fabric over my mouth in the freezing temps. As a “cold handed” person it is good to know that keeping my head and face warm may help prevent the fingers from turning, “corpse white”. I prefer wearing mitts instead of gloves in extreme cold so I can curl my fingers together inside for extra warmth. I also like to wear layers with zippers, the outer layers with full zippers and inner layers with half zippers(how many layers depends on how cold it is) so I can unzip to let the heat escape when I get too hot and zip up again when I get cold.
HI Alex,
The majority of beliefs on heat loss through the head are a bit off. More recently there is information to suggest that the main reason that heat loss through the face/head is greater is because in most instances it is the one part of the body which remains largely uncovered from direct environmental interaction. If you repeated the study you cite from the 50’s but have uniform body (un)coverage then the regional differences in heat loss would be less markedly obvious! PArticularly if you also normalized the heat loss to regional surface surface area. I have data to suggest this is the case and that the head is not one of the major regions of heat loss when clothing coverage is more well controlled. All in all though you are right, in that you do need head coverage, although you should still not neglect coverage of other exposed regions such as the hands and forearms which potentially may experience greater heat loss/surface area.
Great blog! I always read your articles with interest!
@SHFaulkner
@Steve: Thanks very much for the comments (though of course I now wish I’d known that before I wrote the article!). Very interesting stuff. I suppose if the cultural norm was to cover the entire body with clothing except the elbows, I would have been writing about how the body makes a special effort to keep the elbows warm. 🙂 Will you be publishing any of the data on regional (lack of) differences in heat loss?
@EJ: Yes, I find it quite problematic to run with a thin balaclava over my mouth. I only do it when the cold is otherwise intolerable — it’s a “least of two evils” thing. A few friends have specially designed running balaclavas that cover the whole face, but around the mouth have a special low-impedance breathing-mask material. They say it’s much more comfortable.
I’m in full agreement with your other advice. I run in thick fleece mittens even in temperatures about freezing, because I have exceptionally poor circulation in my fingers. I also use lots of half-zip tops to regulate heat. That being said, I find if I’m willing to tolerate being quite uncomfortably cold for the first five minutes of a run, I can settle into a nice thermal equilibrium for the rest of the run. I only have to zip down and up if I’ve started off with more than I really need. (But that’s probably less appropriate for really long runs, when you might have more variation in pace, effort and terrain.)
There was an article about head loss through the head that was published in the Globe and Mail! I recalled it when I read your piece, Alex.
I haven’t read Steve’s research, but I knot that there is research involving cold water immersion (sorry, I don’t have the links) demonstrating that for a person at rest and not shivering, head loss through the head corresponds pretty well to the head’s fraction of total body surface, about 7%. However, the story gets more complicated in other cases. When you begin to exercise, there is an initial surge in cerebral blood flow that causes cerebral heat loss to rise – to as much as 50%. As exercise continues, the body adjusts blood flow and heat loss returns to the baseline 7% rate.
However, if the problem is not to dump heat but to conserve it, so that you are shivering strongly, you can lose as much as 55% of heat through your head, because the body cannot reduce cerebral blood flow as it can to the extremities.
Or anyway, that is my muddled, vaguely remembered, layman’s interpretation. Like you, I’d love to hear more from Steve.
@Steve: I also used to think that most heat loss was through the head, though it kinda makes sense that the body part that least looks like a radiator in most people I’ve met isn’t particularly prone to it. The body parts that most look like it are the lungs. Besides surface area they also have the likely other determinant of heat loss, namely blood flow.
Is there any data on that?
Hi Alex
Some good info as always.
Is there any evidence to support the takeaway for “stay dry”? I’m a heavy sweater and I doubt that it’s possible for me to “avoid sweating in the first place” when I go for a run. I’ve heard that active people tend to start to sweat sooner than sedentary people. (Maybe you have addressed this in one of your articles?) If this is true, it suggests that the sweat response may be hard to avoid. As long as I keep moving I can generally stay warm when I’m sweaty, so my approach is generally to be more careful about the distance as the weather gets colder.
Hopefully I’ll be publishing some of this data during the next 12 months…but you can have a look at some of the papers by Victor Koscheyev who shows similar results.
@RH yes one of the key determinants is as you say surface blood flow, which is one of the reasons heat loss from the hands and forearms is so high as there is a high capillary density close to the skin surface, allowing for a great degree of environmental heat exchange.
@SHFaulkner
One thing to add and already hinted by another reader: the body uses the most heat simply through the area most exposed. The head does not possess some special quality making it different,
http://www.bmj.com/content/337/bmj.a2769.full
To be honest, until one of my readers corrected me in a similar article of mine and sent me that link, I didn’t know that either 🙂
@Evilcyber: Thanks for the link! After the comments above, I’ve been curious to see some actual evidence on either side of this debate. That being said… The BMJ article you cite offers two links to support the claim that the head doesn’t leak heat any faster than the rest of the body. One of the references is a New York Times article which just quotes some scientist. The other is this one:
http://jap.physiology.org/content/101/2/669.long
Here’s a quote from the abstract:
“In both body-exposed and body-insulated conditions, head submersion increased core cooling rate much more (average of 42%) than it increased total heat loss. This may be explained by a redistribution of blood flow in response to stimulation of thermosensitive and/or trigeminal receptors in the scalp, neck and face, where a given amount of heat loss would have a greater cooling effect on a smaller perfused body mass. In 17°C water, the head does not contribute relatively more than the rest of the body to surface heat loss; however, a cold-induced reduction of perfused body mass may allow this small increase in heat loss to cause a relatively larger cooling of the body core.”
So my reading is that — according to this study — the head doesn’t contribute to greater heat loss, BUT it does contribute disproportionately to cooling of the body core. Which would suggest that covering the head IS more important than covering another part of the body with similar surface area…