Is someone who starts sweating sooner fitter?

01 August 2013

Question

Who is more fit: the person who starts sweating as soon as they begin to exercise, or the person who barely breaks a sweat? The former may be thermo-regulating better than the latter, but the latter would seem to be unaffected by the exercise?

Jon

Answer

Ginny Smith - So, that's a really interesting question, but how much you sweat is affected by loads of different factors.

Obviously, the weather: on a really hot sunny day like today, you're going to sweat more because sweat is a cooling mechanism. It aims to dampen your skin then you get evaporation and that cools you down.Now, when we do exercise, of course, we get warm, so we sweat more.

So, it would seem that someone who sweated more would be more efficient. They're better at cooling themselves down, so that's more likely to be someone who's fitter and that was what people thought. There were plenty of experiments that seemed to show that. They got some unfit people and they got some fit people, and they got them to do exercise so that they were exerting themselves the same amount, and the fit people sweated more.

But, when you look at this a bit more carefully actually, the difficulty comes in how you determine that someone is exerting themselves by the same amount. So, what they did here was they looked at the maximum oxygen efficiency which is a kind of measure of fitness and they got people to work at 60% of how hard they can work. So, the fit people were obviously working a lot harder to get to that 60% than the unfit people were and they were sweating more. But when you look at it more closely, because the fit people were having to work harder, they were getting hotter.

It seems that if you're fitter, yes, you can run faster and use the same proportion of your maximum oxygen usage, but you're still making more heat because you're running faster. You don't get any more efficient at running without producing heat. So actually, these fit people were just getting hotter and therefore, sweating more.

When they did the experiment, but they controlled for the heat that the people were producing, so they made the unfit people and the fit people run to produce the same amount of heat, they didn't find very much difference in their sweat apart from on their foreheads. In fact, the unfit people seem to sweat more on their forehead, which is a bit surprising and unusual.

So, I think just looking at two people in the street who are running along and seeing that one person is sweating and one person is not, you can't really tell anything about fitness levels because of course, there are other factors that affect it as well. So, women on average sweat less than men and larger people will sweat more than smaller people because they've got a larger volume compared to their surface area, so they find it harder to cool down.

So, it's kind of hard to tell, but it doesn't seem that there's a huge difference once you control for this heat production.

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