If there's something rewarding about a session of physical exertion, riding to work or mowing the lawn, less pleasant is peeling the wet, clammy shirt off your back.
Why you get hot with exercise was a long held puzzle that was finally solved in the winter of 1782-1783 by Antoine Lavoisier and Pierre-Simon Laplace.
Lavoisier had been investigating the theory that combustion releases of a fire-like element called phlogiston. "Phlogiston" comes from the Ancient Greek which literally means "burning up".
To test the theory, they placed a live guinea pig (really!) in an apparatus they called the "calorimeter".
The hapless guinea pig was inside, packed with snow around a shell of ice held at a constant zero degrees Celsius.
By measuring the carbon dioxide exhaled and heat produced by the guinea pig, they were able to conclude that respiration, is in fact, slow combustion.
Or, as Lavoisier put it, it was "like that of a candle burning". And, in the process they were disproving the phlogiston hypothesis.
The short version is that your body "burns" organic molecules (sugars, fatty acids or proteins) to fuel muscle movement. This process produces heat. Quite a lot of it actually.
A modern experiment showed that a person could generate 147 watts - about enough to power a couple of old incandescent light bulbs. But, at the same time, their metabolism was consuming around 650 watts.
That means, during exercise, 80 percent of the total energy is converted to heat, while only 20-25 percent is working your muscles.
It also means your body is not like an internal combustion engine which uses heat to expand a gas to push a piston.
Instead, there's an intricate chemical process in your muscles that - to put it crudely - "walk" tiny notches, causing them to contract.
How high your body temperature rises during exercise depends on factors such as the type of activity, ambient temperature, humidity and your fitness.
To keep cool your body shifts blood flow closer to the skin. You breathe faster and sweat.
Your body's thermostat - the hypothalamus - monitors thermoreceptors in your skin and core to maintain a normal 37 degrees Celsius.
In the true sense of the word, it's a vital function because your body can only operate in a narrow range. Much beyond 37 degrees risks the lethal condition of hyperthermia.
Now you might be wondering if all this relates to the strange cases of spontaneous human combustion. For an answer to that mystery, stay tuned.
The Fuzzy Logic Science Show is on 11am Sundays on 2xx 98.3FM. Send your questions to AskFuzzy@Zoho.com; Podcast: FuzzyLogicOn2xx.Podbean.com
