What influences sweat rate variations among individuals?

[bbrauer]

I recently started teaching some spin classes at the local health club. I notices that, in contrast to the civilians who I'm flogging, I sweat so much that there's a little lake underneath my spin bike, and my shoes are squishy and leave little puddles when I take a step (thankfully I got an old pair of cycling shoes and don't use my nice Sidis for the spin class). I don't get that on the bike outside for the obvious reason that a persistent 18-20 mph self-generated wind aids in evaporation. I do notice that my helmet strap gets pretty crusty with salt pretty quickly.

It got me thinking if there was a direct correlation to sweat rate with energy output - as in the higher your fitness or the harder you work, the more heat you generate as a byproduct, which necessitates a higher sweat production. Or maybe it varies individually based on the body's efficiency in regulating heat....or likely a combination of several factors.

 

[limerickman]

Interesting topic.

Sweating is the human bodies mechanism for cooling the system once the core temperature increases.
What triggers an increase in core temperature?
And what triggers the cooling system (sweating) to begin processing?

Core temperature increases when the rate of activity in the body begins to increase or when the body becomes stressed (emotional stress/fear/panic)

However the trigger for the cooling system, in both instances, is controlled by the hypothalamus – and when the hypothalamus registers a core increase in temperature, a hormone is released to the sweat glands to secrete perspiration (sweat).

Physical emission of perspiration is therefore regulated by a person hypothalamus and these emissions are not necessarily related to how hard the body is working.
For example a friend of mine suffers from head sweats : he starts sweating very heavily for no apparent reason.
His doctor told him that this is due to his hypothalamus engaging when it shouldn’t.
The reason why it engages is due to underlying stress disorder. When stressed, he sweats.

Therefore, the amount of sweat generated, does not equal the level of energy expended by a person. It is a measure of hypothalamic activity. And some people sweat more than others and the threshold for sweating differs in many people.

 

[64Paramount]

Yeah, that is an interesting topic.

I've always sweated a lot when I excercise. For example, today I went for a 32 mile ride and I lost 2.5 pounds. I drank a large bottle of water on the ride, but I think I just sweated out 2.5 pounds of water on the ride. (Or more, if you count the water I consumed during the ride)

Is that normal? I don't know, but I've always been that way.....

 

[Piotr]

Sportsscientists.com have some articles on hydration and cooling. It's been a while since I read them, so I'm not sure if they'll aswer your questions. The comments can be quite insightful as well.

 

[dhk2]

Agree power output on the spin bike determines how much extra heat the body has to dissipate. Consider we're only about 25% efficient in converting energy to useful work. So, when pedaling at 300 watts output, the body needs to lose another 900w to avoid overheating. I've seen an analysis that calculates the max time an elite rider can generate 350w indoors (at normal room temps, w/o cooling air) is somelike like 12 minutes. At that point, core body temp is up 2*C, which forces the rider to stop.