Dec 18, 2008 at 1:10 pm #1232719
Don WilsonBPL Member
@don-1-2-2Locale: Koyukuk River, Alaska
I pulled this little snippet off the web today. I thought it was interesting since most of us have probably lived with some form of this maxim re hats and the cold. What do you think, BPLers? Here is the quote:
We've all been told to put a hat on in winter because most heat is lost through the head.
The researchers even found that the US Army Field manual for survival recommends covering your head in cold weather because around 40-45% of body heat is lost through the head.
A recent study, however, showed there is nothing special about heat loss from the head – any uncovered part of the body would lose heat.
Scrutiny of the literature shows this myth probably originated with an old military study in which scientists put individuals in arctic survival suits (but with no hat) and measured their body temperature in extreme conditions.
If the experiment had been done with the participants wearing only swimsuits they would not have lost more than 10% of their body heat through their heads, the researchers said.Dec 18, 2008 at 1:26 pm #1465207
@derekoakLocale: North of England
This is true to a point but the body allows limbs to cool to conserve heat for the core. Once the limbs are cool heat loss from them is reduced anyway. The head is part of the core, the body keeps pumping heat in. So insulating the head is more beneficial than insulating the limbs.
I think the "researchers" had an eye on being journalists.Dec 18, 2008 at 1:28 pm #1465209
@arichardson6Locale: North East
I read that article also. I thought the other debunked myths were pretty interesting. Here is a link for anyone interested: The Article
I think the point is kind of moot. Yes, any area of the body left uncovered will lose heat. The fact that most people wear pants and long sleeves in cold weather, not swimsuits, means that the head is left uncovered and thus, when you cover it you can be warmer. I thought it was crazy though since I have said and heard more times than I count the whole 40-45% thing. Still, I find it a silly study because yeah, if you want to be warmer, cover yourself up :-)Dec 18, 2008 at 1:29 pm #1465210
Chris TownsendBPL Member
@christownsendLocale: Cairngorms National Park
Is this really new? I always thought that the advice to wear a warm hat was based on the rest of the body already being adequately clothed. I don't think anyone has suggested that if you were naked in cold weather putting on a hat would warm you up! Also, up to 10% heat loss sounds significant to me. You could soon get very cold if that continued.Dec 18, 2008 at 2:58 pm #1465243
Karen WilsonBPL Member
@kwilsonLocale: French Pyrenees
Probably moot in the sense that anyone with common sense will cover up most exposed parts anyway, but I guess the "myth" was that "most" body heat was lost through the head – 40 plus percent in that old Army field manual (which still isn't "most", but let's not go there).
I've run across a few folks who claim they can hike in shorts in the winter so long as they wear a hat. I remember a long conversation on that topic with a hiker I might in Vermont in an AT shelter many years ago.
Anyway, just thought it was interesting.Dec 18, 2008 at 4:49 pm #1465269
te – waBPL Member
i think the important issue is the aortic arch leading to the two carotid arteries that carry core-temp blood to the brain. The brain gets the freshest, warmest blood via these 2 arteries (and 2 found in the back of your neck, the "vertabrals")
thus, it is true that the warmest blood goes to your head first.
from what I have experienced, i would rather have on a nice hat than a base layer. fwiw, my 2¢Dec 18, 2008 at 5:20 pm #1465273
Tom KirchnerBPL Member
@ouzelLocale: Pacific Northwest/Sierra
I'm with Michael on this one. I don't know about 40% but, if I am cold and want to warm up quick, a hat and a wind shirt are the first pieces I put on. Vice versa when I begin to overheat. Also, I wonder what the results would be if they were measuring heat lost/square inch of surface area? Those carotids are big and very close to the surface.Dec 18, 2008 at 6:14 pm #1465281
Dale WambaughBPL Member
@dwambaughLocale: Pacific Northwest
Re: Army manuals and science:
This is information aimed at training teenagers to stay alive in the most horrible conditions imaginable– bad weather, mass confusion, uncertain support, and the most extreme violence possible.
Along with 10,000 other details delivered in a few weeks, the message is put your hat on and keep your feet dry. Mommy is a guy with three stripes on his sleeve and bad manners. Now, go jump out that airplane or out of the landing craft and up the beach while the other guys try kill you. .Dec 18, 2008 at 7:05 pm #1465293
Michael MartinBPL Member
@mikemartinLocale: North Idaho
To a certain extent, you can shift your "personal insulation" around to maintain warmth — e.g. wearing a hat instead of a windshirt, etc. Your blood flow will even out the cold and hot spots…a bit.
In fact, the highest warmth per weight ratio of your insulation will be found by insulating the warmest parts of your body (e.g. core) proportionately more than cooler parts. That's why torso-length sleeping pads are so effective.
But, there are some limiting factors:
1) If any part is too insulated, it will sweat, even if you're cold overall. Sweat is bad. It's counter productive to staying warm. Plus, the moisture will end up in your clothing and cause more problems later on.
2) Your body conserves heat by preferentially cooling the extremities as Derek noted. But, there is a lower limit. You may be able to achieve "heat balance" by adding a parka or hat, but if your fingers and toes get too cold, you can lose dexterity, get frostnip/bite, suffer nerve damage, etc. (Unfortunately, I've experienced all of the above…) :-(
-MikeDec 18, 2008 at 8:34 pm #1465310
Ron DBPL Member
This thread reminded me of one this past summer that went into much more technical detail. This is the one of the comments from Richard Nisley that has a nice discussion of heat output percentages under different conditions.
( richard295 – M)
San Francisco Bay Area
Re: Re: Re: COCOON PRO 60 Parka? on 07/31/2008 13:01:45 MDT Print
The Cocoon UL 60 Hoody will provide the same temperature rating as the Cocoon PRO 60. The difference is a significant reduction in the ability to keep external moisture out of the insulation with the Cocoon UL 60 Hoody.
The Cocoon pullover provides 7% less body surface area coverage than the Parka. Non hypothermic environments would result in this garment providing a 10% commensurate reduction in warmth. In hypothermic environments this garment would provide 55% less warmth than a hoody.
The body’s primary defense against the cold and hypothermia is vasoconstriction of the peripheral circulation from the normal ~ 4 quarts/min. to .02 quarts/min (99% reduction). This shunts blood to the core and reduces circulation to the skin. The blood flow to the brain does not change as the demand for oxygen is constant. If you continue to loose heat and begin to shiver, you are doing a special case of exercising. The shivering muscles increase metabolic demand and cardiac demand so you increase your cardiac output and the % of blood heat loss through your head to about 55%.
– When not shivering, the heat loss from the head’s 7% body surface area is ~10% of the body’s total heat output
– Shivering increases heat output ~ 5x
– Shivering increases head and neck heat loss (10 X 5 = 50) to ~55% of your body’s totalDec 18, 2008 at 9:45 pm #1465319
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
Either the researchers or, far more likely, the journos, have displayed a degree of ignorance here which can be fatal. I despaired a long time ago of journos, but I am beginning to despair over the current crop of young 'researchers' too – especially when they step outside their very narrow range of knowledge.
> because around 40-45% of body heat is lost through the head.
Make that 'up to 40-45% of body heat CAN be lost through the head' and you would be right. Marvellous how changing one word can alter the whole meaning.
> A recent study, however, showed there is nothing special about heat loss from the head
> – any uncovered part of the body would lose heat.
True in itself – of course. BUT…
When your arms and legs get cold the blood flow to them reduces in order to save heat for the core and head. OK, you end up with frostbite of the extremities, but you live.
When your head gets cold, by just a degree or two, you first go stupid and then you die. No frostbite, just shutdown. There is a difference!
> Scrutiny of the literature shows this myth probably originated with an old military study
I dare say the information comes from an old military study, but I wouldn't call it a myth. It is very real.
> If the experiment had been done with the participants wearing only swimsuits they would
> not have lost more than 10% of their body heat through their heads, the researchers said.
Ahh… yeah, right. So you stand there in the middle of the snow field in a swim suit and you get cold all over. Why am I not surprised?
The root of the story lies in the fact that your body will, come what may, keep shunting more and more hot blood to your head to keep it at 98 F whether or not your extremities are freezing (literally). So you may feel OK because your head is warm enough – while you slowly get frostbite in your hands and feet.
CheersDec 18, 2008 at 11:15 pm #1465335
@cbertLocale: N. California
So then I should be fine hiking naked in Antarctica as long as I'm wearing my ultralight hoody, right?Dec 19, 2008 at 8:46 am #1465373
John S.BPL Member
Cary, yes, and your feets wont get cold either since you are wearing your hat. ; )Feb 17, 2009 at 9:42 am #1478430
Eric BlumensaadtBPL Member
@danepackerLocale: Mojave Desert
What Roger Caffin said. Absolutly. Seems "new" research implies human physiology has suddenly changed. Uh huh…
Neck and head veins do NOT vaso-constrict when exposed to cold, as do the veins in the rest of the body. The brain is the TOP priority in getting warm blood. The neck and head constitutes the best readiator of heat the body has due to this lack of vasoconstriction in the cold. Remember, the brain has a very narrow "optimum operating temperature range". If the brain gets too cold you will become hypothermic, with befuddled thinking being a serious warning sign.
That said it's silly to believe one can dress the body warmly and neglect head/neck insulation. In fact for LIGHTWEIGHT CLOTHING for constant motion travel proper head covering should be able to compensate somewhat for having less clothing on your limbs. Adequate head and torso insulation, with less insulation on limbs is a common method of dressing for winter travel without overheating.
Listen to your body, not "research" that purports findings contrary to actual experience.
EricFeb 17, 2009 at 2:21 pm #1478477
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> the brain has a very narrow "optimum operating temperature range". If the brain gets too cold
> you will become hypothermic, with befuddled thinking being a serious warning sign.
Too cold is a danger, but so is too hot.
I remember one day when it was nearly 40 C and very humid, and the track was white and there was little shade and we had little water left. We came across a large puddle of very muddy water. We were not that short of water that we needed to drink this stuff, but it was shaded and cool. So my wife used a cup to pour this cool water over the back of my head and the top of my neck: the top of the brain stem in other words. The sheer ecstasy induced by the cold water cooling down my overheated head was incredible!
Very sensitive thing, the brain. Look after it: you only have one. (Although less than one seems possible in some cases.)
CheersFeb 18, 2009 at 12:47 am #1478608
Rod LawlorBPL Member
I've heard a rumour that they are born with two. Apparently many of them are then only half strength, which is a problem when they do the cosmetic surgery. If they throw the brain away with the second head instead of implanting it in the 'keeper' it appears to highly value the logging of old growth forests. Who knew?
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