eli5: How does the body store power
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Basically sugar. Muscles store power in something called glycogen which is a bunch of glucose (basically a kind of sugar) molecules connected.
In the long term, the body stores energy in fat. Fat is a kind of cell that exists to store caloric energy for later use. If you eat a bunch of potato chips and don’t exercise, your body breaks down the carbohydrates into more simple sugars for the muscles to use, but you don’t use them. So the excess are picked up and held by fat cells.
If you go through a period where you don’t eat a lot and do a lot of work, then your muscles burn off a lot of sugar, and the fat cells release more into the body to compensate.
Short answer, chemicals. The shortest term form of power in your body is a molecule called adenosine triphosphate (ATP). Some of amount of ATP is floating around in your cells right now. When your cells need energy they will consume the ATP by converting it into other chemicals. This chemical conversion process creates energy as a byproduct.
The next closest store of energy is sugar. Sugar can quickly be converted to ATP which can then power your cells.
Longer-term, fat can be converted into sugar. But, this process takes longer.
The body has a number of energy-storage molecules.
The most immediate ones are glucose and other sugars, which are dissolved in your blood and can be picked up very quickly. Your body doesn’t store much simple glucose at a time, so this supply runs out very quickly under demand, and your body has to replenish it from glycogen in the liver (see the next paragraph).
The next, and largest short-term, store is [glycogen](https://en.wikipedia.org/wiki/Glycogen), a molecule that is built out of a branching bundle of glucose molecules. Glycogen is stored in your muscles and liver to provide extra energy on demand. The glycogen stores in your muscles are enough to support normal exercise, but you can burn through them with very vigorous and sustained exercise relative to your level of fitness (and it takes a little while to recover). Improved glycogen storage in muscles is one reason why regular exercise makes you stronger and able to endure for longer.
The last major form of storage is body fat, which is more compact and is used for long-term energy storage. Fats are harder to produce and break down, so they’re not as immediately available as glucose from glycogen is, but they can store more energy per weight and so they’re used to support storage over months or years. When the body is low on energy for long periods of time, the body breaks those fats down to produce the glucose it needs.
The main way is by phosphoryl bond energy. there are certain molecules with unstable, high-energy chemical bonds that are used as energy “currency”. When the bond is broken, it releases energy. You can spend this currency to get power to do stuff. Eating sugar, burning fat, burning carbs, burning amino acids… this all can generate energy currency to spend later. Our bodies have evolved tons of enzymes that act as machines that couple two things at once: accept energy currency, and perform some chemical reaction or function. Ex. Muscles accept this currency and break the phosphoryl bond, using the energy released to move. Enzymes accept this currency to catalyze difficult reactions.
The most common energy currency is called ATP. It’s basically just a ribonucleotide “handle” that is an artifact of the RNA world. It’s sole job is to carry this high-energy phosphoryl bond, and to be recognizable for binding purposes. This molecule is nice because it’s reactive, not too unstable (so it won’t fall apart before it’s spent). Sort of a ‘goldilocks’ molecule.
Both substrate-level phosphorylation and oxidative phosphorylation store energy as ATP within that phosphoryl-anhydride bond.
Electron Bifurcation is the other method of energy conservation, which conserves redox energy directly as chemical potential on a stored electron… but that’s light years beyond eli5
Your body uses three main fuels for storing energy: ATP, glucose, glycogen, and fat. For short term energy storage, on the order of seconds, ATP is what is used. ATP is often called the energy currency of the cell, as everything your body does ultimately is powered by ATP.
Glucose is the main sugar molecule used by cells of all types to burn for energy. When your blood sugar levels are low, your liver cells produce glucose and secrete it into your blood stream for your brain neurons to take up and use as energy.
Glycogen comes next, and is used by muscles cells for short-medium storage of energy. Glycogen store last several seconds, I believe as much as 30 seconds. Glycogen is what makes dark meat dark in color, and why it tends to be a bit sweeter than white meat.
Finally,for really long term storage, your body uses fats, called triacylglycerides. These TAGs get stored in fat cells, and your body uses these as energy when food is scarce and you are burning more calories than you are consuming.
Glucose, glycogen, and TAGs are all converted into ATP before they can be actually used as energy, because again ATP is the energy currency of your cells.
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