We humans are a type of animal that generate our own heat through internal chemical reactions. Unlike some other animals (like lizards) we need to keep our temperature in a narrow range, otherwise bad things will happen to us. When our temperature rises too high we call it hyperthermia; when it gets to low we call it hypothermia. Our temperature rises as a result of exercise but obviously that’s not the only reason – our temperature can also rise through absorption of heat from the outside. But for the purpose of this article, I’m only going to deal with the internal aspect to heat production and dissipation. Sound like fun? Then read on brothers and sisters.
So you’ve all experienced it: running for a bus; sprinting up a hill on your bike; doing push-ups on the bow of your yacht. It isn’t rocket science – you exert yourself, you get hot. But why? It has to do with thermodynamics and, specifically, entropy. Oh no, here comes a flashback from when you were 16 years old… (or that old Flanders and Swan song – Ed)
What follows is a very simplistic explanation, but it should do the trick…
When energy goes from one state into another you lose some of that energy as heat. Here’s an analogy that actually makes sense: when a coal-fired power station turns chemical energy into electricity (by burning) not all of the chemical energy turns the turbines – some of it lost. Likewise, when the chemical energy in the food you eat is transformed into ATP (the molecule responsible for muscle contraction) the transformation process is not 100% efficient. Some of the chemical energy is lost as heat, or, we could call this entropy. Now here is where it gets more interesting:
We humans have several different ways of making ATP inside our muscles. Some are more efficient than others. At low intensities, when we only require small amounts of ATP (like walking), we are most efficient. Let’s suppose we are 40% efficient in this instance. This will mean 60% of the chemical energy from your food is being lost as heat to the surrounding tissues in the body. When the demand for ATP gets higher (like running), the chemical conversion gets even less efficient. At a mildly intense jogging pace you are probably only 25% efficient at creating ATP, so 75% of the potential chemical energy is being turned into heat. When you are in an all out sprint, you are probably about 10% efficient – and so about 90% is going to heat. That’s a lot of entropy. And that is why the harder you work, the hotter you feel and the more you’ll sweat. I think I’ll explain about sweating at a later date…
Why you need to stay warm (but not too warm) when exercising
Some heat generation is beneficial to help speed up chemical reactions in the muscle. But excessive heat can adversely affect muscle contraction.
Chemical reactions in muscle cells (and within all your body) are controlled by enzymes. These chemical reactions are what allow muscles to contract. It’s a bit complicated, but basically an enzyme is a protein which speeds up a chemical reaction within your body. Forget about the enzymes you may have heard about in laundry detergents or digestion for a moment, every cell in the body has enzymes in them. We have specific enzymes for specific chemical reactions. These chemical reactions take place on a second by second basis inside our bodies – and – if they happened too slowly we would die. Quickly.
Enzymes facilitate faster reactions – allowing all body cells to work as efficiently as possible. Heat itself can also make a reaction happen more quickly: drop a spoon full of sugar into a glass of cold water and see how long it takes to dissolve. Do the same thing in a glass of warm water and see the difference. It’s the same in our body – the hotter we get the faster chemical reactions happen in our bodies. Up to a point. The heat can get so high that the enzymes can “denature” (die). If you want to visualize what this looks like then think of an egg. Or specifically the white part. Egg white is pretty much all the proteins that go into the formation of a bird. When you heat egg white what happens? It turns opaque and gets tough. The proteins in your body can undergo the same process – they coagulate, change structure and lose any semblance of what they were intended for. Excess heat can cause enzymes to deform like a GI Joe held over an open flame. The plastic will bubble and twist and pretty soon it won’t look like a GI Joe anymore and it definitely won’t be able to fight Cobra. If your enzymes get too hot they will twist and deform and they won’t be able to perform their function either.
My next article will be about how our bodies keep our temperatures down when we exercise. This will be useful to know because the days are getting longer and hotter for us in the Northern hemisphere and you’re all going to be outside jogging up a storm this summer. Right? RIGHT?!?!?!
Please leave questions or comments below!
You can read all of Matthew’s series on fitness here