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.
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! :)
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.
Eliot blog thing
- strava thing