Short, intermediate, and long-term supplies
Animals have three mechanisms by which they can convert stored energy into work. The first is what carries Usain Bolt through the entire duration of his 100m dash. We can typically sustain only about 20-30 seconds of this maximum energy drive before we have to fall back to the “medium” level of energy expenditure. This medium term one also falls back to the more long-term energy store.
Mechanisms:
Oxidation - turning fatty acids into ATP (in the mitochondria). Oxygen in, lots of ATP out Glycolysis - turns carbs into ATP. Does not use oxygen, and produces less ATP Energy Recycling - turns ATP into ADP by losing a phosphate. Creating can provide a replacement phosphate.
ATP is the fuel we call upon. ATP losing a phosphate (and turning into ADP) creates a waste hydrogen atom and gives us a set amount of energy. But we can recharge them. We only have about 100g of ATP in us at any given time, but we use our entire body weight worth of ATP over a given day.
The phosgene system - the short, quick burst energy system. Uses ATP we already have ready to go. Creotine phosphate is what happens after we run out of ATPs. This gives us time to start up glycolysis.
Glycolysis breaks sugar down to give us back our ATP. This creates lactic acid, too. Glycolysis is the medium-term energy process.
Using oxygen to burn ATP (aerobic metabolism) creates more energy, but happens slower. This is what VO2 Max measures. VO2 max you can increase by training, and it’s the mechanism behind 80% of the energy supply if you run in a mile.