Low surface to mass ratio - therefore the ability to shed heat via blood flow to the surface or by sweating is decreased.

Frodo might be tall but he is lean...he has decreased his mass but his surface area remains relatively stable. He could gain 20 pounds of muscle mass and not add much surface area (hence lowering ratio)

I am 6'2 and 195 pounds with 9% body fat at the moment. I raced my fastest - running not triathlon - when I was 173 pounds. I felt weak at less weight and heavy at more. I also race and train in SW Florida - or as I like to call it - the amazon jungle.


Im sure someone can shed WAY more light on the principle but this is what I gathered when I tried to figure out why my out of shape 5'4 buddies didnt die in the heat and I did

The simple explanation is that bigger people have more muscle leading to more heat that they have to dissipate. The amount of heat that you can dissipate depends on the amount of skin that touches the air (surface area).

The rate that heat generation increases with size outpaces the rate of surface area increase with size, so the bigger you are, the harder it is to shed heat. You can alleviate this somewhat by staying skinny but for the most part it's a fundamental law that cannot be changed.

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I like analyzing things - http://engineeringfitness.org

I don't think that is quite right.

Bigger people do have more muscle and generate more heat. So you're good there, but comparative surface area does not increase compared to mass with size.

The relationship between surface area and mass on smaller runners is such that smaller runner simply have less surface area as well. As mass increases on a human the surface area does not increase exponentially. My wife is 5'0 and weighs 95lb. I am only 1'1" taller but weigh 180lb, almost twice as much. (I know mass and weight are not the same thing but ...)

So, smaller runners have more surface area. They also generate less heat. It's a double win for them in the heat as opposed to the single win described earlier ..... and that pisses me off! :)

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https://www.pbandjcoaching.com
https://www.thisbigroadtrip.com

Need to look around a bit more.

Full answer here.

http://www.samiinkinen.com/post/64273562229/how-can-mirinda-carfrae-run-a-250-marathon-in


Does that help? :-)

Actually, you're both kind of saying the same thing, but JayPeeWhy, I'm not sure you realize it.

To drastically oversimplify it, call a human a sphere with radius r. Big people have a bigger r and small people have a smaller r.

Surface area increases with r^2, but volume increases with r^3. Your volume is what generates heat, and your surface area dissipates it. So with your r^3 term outpacing the r^2 term...there ya go...bigger r means trouble in the heat.

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Eliot
blog thing - strava thing

If you actually read my link it will explain it in more detail

yeah, i think we're all talking around some version of bergman's rule and allan's rule. this is me explaining them in a lecture a while back:

https://www.youtube.com/watch?v=2n-Nkup_uQc

in short, you combine the idea that hot weather animals are usually less massive than their cold-weather counterparts with the idea that there are some interesting geometrical rules about the relationship between volume (mass) and surface area.

you're onto something with the sphere idea; darwin wants people in cold climates to be more spherical (short appendages, more central body mass) and hot climates to be cylindrical (long and lean). the cylinder gives you more surface area for the same mass compared to the sphere.

so all else equal a longer, leaner person is able to radiate heat better than a shorter, rounder one.

of course none of this addresses differences in fitness, clothing, pacing, nutrition, and etc etc.

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https://lshtm.academia.edu/MikeCallaghan

http://howtobeswiss.blogspot.ch/

Thanks, great article.

Correct. I read that they thought surface area percentage increased more with size but that it could not keep up with comparative heat production. But that's not what he/she/they they were saying.

I see their user name is Stumpy, so there may be some vested interest in physics that play to their advantage.

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https://www.pbandjcoaching.com
https://www.thisbigroadtrip.com

When the dimensions of a volume are multiplied by x, its mass is multiplied by x^3 and its surface by x^2. The bigger you are, the more mass you have that produces heat, in relation to the surface available to dissipate that heat.

I did read your link before I posted, and it absolutely makes a more complete explanation. However, sometimes a more simplified explanation helps to get everyone on the same page :)

(great link, too)

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Eliot
blog thing - strava thing

Could the inefficiency of someone's ATP production in their mitochondria contribute to lower heat tolerance? Essentially, do some people produce more heat than others for the same effort, and if so, should they be allowed to stash frozen hats on the race course?

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Oui, mais pas de femme toute de suite (yes, but I am not ready for a woman straight away) -Stephen Roche's reply when asked whether he was okay after collapsing at the finish in the La Plagne stage of the 1987 Tour