I could not find in the many posts if this link had already been posted, but gives some addtional information for thought and (IMHO)makes the issue more complex.

Pete
Heat Loss Thorugh the Head - Update

The actual statement of the "myth" is: "Up to 75%" means it can also be significantly below 75%, including its normal 7-10% -- the "myth" isn't much of a myth. Later in the article the author states, I just don't see what the argument is about. These statements are not contradictory.

That was my feeling for the site. It a blog that claims to present the latest in wilderness medicine (which may or may not be true), but a comparison between it and the journal Nature reveals huge differences between a true peer reviewed journal and "TMC Books, LLC is just three guys working out of an old barn in the White Mountains of New Hampshire." (follow the 'about us' sections to TMC books, the company that publishes the Wilderness Medicine Newsletter. When relying on research, especially where it concerns my health, a publication with a lack of peer review isn't going to be my first choice. For that matter neither is Discovery Channel, Mythbusters, or even this site so far as it concerns medicine or similar subjects. Scientists generally try to present serious new research in a peer review article, if they don't you have to ask why.

And for the record this is the very place a person would question the authority cited and determine whether a fallacious appeal to authority is being made.

Hey, I like Mythbusters, at least they show you their methodology and at least seem to let the chips fall.

I propose that the sapient quote from the update you link to is found here:



In this case, the excercising test subjects, the increase in heat loss through the scalp was temporary (I would say a matter of minutes, but that's just my opinion), and returned to the 7% figure. The ONLY exception listed here (and I did refer to this in an earlier post), is the shivering hypothermia victim, which again, I feel is too limited a population to base our general heat loss figures on.

Instead of making the claim, "Wear a hat because you can lose 55% of your bodies heat through your scalp.", It would be much more accurate to say, "Wear a hat because you can lose 10% of your bodies heat through your scalp, unless you happen to be a near death hypothermia victim in which case it jumps to 55%."

Great show. If more TV was like that, I'd consider owning a TV. But not the place I'm going to go to find out the best way to treat a possible heart attack while I wait for the paramedics (not that I think they'd do a segment on that).

One other possible issue with the “study” is the methodology or measuring device may not have been able to detect all forms of heat energy being loss. Was the device capable of measuring radiant, convection and conduction forms of heat loss? Or just measuring skin or core temperatures. Remember the adage is based upon the percent of heat loss through the head, not just relative temperature of the head compared to other parts of the body.

Pete

Temperature change is a measure of energy lost from the body. Measuring radiation, sensible and evaporative convective heat loss to the atmosphere would just tell you the mechanisms, and would not change the total heat loss.

These studies are based on the energy conservation principle, so that

Net radiation + Sensible convection + evaporative convection + metabolic heat production + change in heat storage = 0.

Change in body temperature, multiplied by body mass and specific heat, give you a change in body heat storage.

No Stretch, I think you're being clear. Here is my theory on how this came to be. The military needed to research how their soldiers' bodies adapted to cold weather (among other things of course). With the best instruments and methodology available in 1957, military scientists carried out said research and papers were published announcing the results. Somewhere in that research a figure was stated claiming a percentage of heat lost from our heads (I'm still not sure what the figure was, I've always heard 70%). Through the years, this information was passed on from study to study, article to article, and mouth to mouth until it became the undisputed fact.

Now, several decades later, more up-to-date research is being conducted and more accurate figures are being presented. I understand your point that it's not "my" facts that need to be proved and I agree, but I don't agree that it comes down to "Doc Gordon" against the world. I'm confident that as we hear more and more about this, the 10% figure will eventually become the new accepted figure (or I will eat that humble pie!).

Why do I think this? If we lost 70% of our body heat from our head, your dearly loved empirical evidence should allow me to walk outside in 30 degree weather with nothing on but a warm hat and maybe a pair of light cotton shorts (or anything else that covered 30% of my BSA) and be warm, I don't know about you, but that doesn't work for me. I do wear a hat when cold, but when I take it off, I don't suddenly start shivering and hypoventilating as I would expect from such a drastic heat loss.

You are more then likely correct, but what I am saying or trying to say: Is measuring either skin temperature or core temperature really measuring total heat loss from the body? Since compensatory mechanisms exist within the body (shunting, shivering, etc.), core and skin temperatures will be maintained until heat loss exceeds the body’s ability to maintain thermic-homeostasis. Therefore measuring core or skin temperatures are only a measurement of the body’s ability to maintain thermic-homeostasis, not heat loss. To the best of my understanding measuring core and/or skin temperature is not measuring heat loss through radiation, convection and conduction.

It would seem to me, if one wants to measure total heat loss, then thermal imaging is necessary.

Pete