h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I heard somewhere that if you are fit, then you sweat after less exercise than if you are unfit. But how come fat people sweat a lot if they exercise?

SP

Bigger mass to surface area ratio means that large people lose heat less easily through standard radiation conduction and convection
Sweating is more efficient at cooling than these and so large people sweat more as they need more heat loss than smaller people.

no sweat!

(ok, bad joke!)

I wish I could say the same, I went down the gym this morning and produced buckets of the stuff.

If someone very thin walks a mile at 5 mph, and someone very fat walks the same distance at the same speed, isn't the actual work done by the fatter person more? They have to move a heavier load, in effect. This could lead to feeling hotter and sweating more, too.

Anything in that, or not?

Reckon so.

I was assuming an equal amount of work with my explanation.

Sweating regulates body temperature by cooling the skin, which cools the rest of the body by heat transfer. Presumably a thick layer of fat would act as a kind of insulation blanket, meaning the skin needs to be cooler for longer to cool the rest of the body, thus necessitating more sweat. Maybe

makes sense - sort of blubber backwards

Yes, rebbulb - well, someone had to say it, eh?

Rebbulb? Isn't that what you do with your garden when your daffs have gone to pot?

I thought it's what they screw into the light fittings in brothels...

You see what happens when Skankyrich comes along?

A fit person sweats more easily than a sedentary person because, like any other system in the human body, the more often you use your sweat glands, the better they function. Exercise triggers the mechanism because as you increase your efforts, you burn more fuel in order to do so. The extra waste heat must be disposed of.

If I strapped 130 pounds to my back, stood up from a chair, and walked forty feet, I'd be feeling the strain. As a result of the extra strain, my body would burn more calories and create extra waste heat, and I might sweat a little. A 300-pound man does that same amount of work every time he gets up to go to the bathroom. This is partly why obese people always seem to be tired and out of breath.

Ah, that's interesting. So you're saying circumferancially challenged people sweat more because their sweat glands are used more often and are therefore more efficient? That makes sense.

In fact, my theory doesn't stand up too well () when you consider that a diameterally exaggerated person would have a greater surface area too, meaning there would be more body for the sweat to cool down and making cooling more effective. Which begs the question; what greater proportion of skin would a 20 stone person have compared to a 10 stone person, for example?

well, to use your "circular" analogies:

surface area is proportional to R^2
volume is proportional to R^3

So a change in mass means a change in volume (density is about constant). However, the corresponding change in surface are is not linear, it would go up as R^(2/3)

For the larger mass = larger volume = larger R the person would, in absolute terms, have more cooling surface. But depending how you define it, their efficieny should be worse, as they have a lower ratio of surface to mass.

What Arnie said. I don't think anyone so far has offered a theory which is invalid. I think they all come together to explain certain aspects of the question. It's a combination of all these factors... insulating properties of fat, decreased surface ratio, extra workload, and increased efficiency of sweat systems due to regular caused by the previous factors.

"... due to regular USE..."