After lifting a few weights, or running, or whatever, we need to rest a while before we can get going again. I can lift weights for a while, then I need to rest a few minutes before I can continue. I don't need to refuel (eat) for some time to have more energy later. What is going on inside the body that lets us return to work so quickly? It only takes a minute or two, and I can lift the same weights almost the same number of times. Of course I'm pacing myself, maxing out. But I would like to understand what this is, where I can find more information to study it further. I know it's physiology, has to do with energy, but that's about it. EDIT: Whoops. I guess this belongs in Homework & Coursework Questions> Other Sciences Sorry.