This fast energy system is your maximum effort, short-duration system. It can supply an intense burst of energy for around 10–12 seconds before it runs out of steam and the next system takes over. This is used when you are jumping, lifting something very heavy, or doing a fast and short run, like sprinting across a basketball court.
In terms of nutrition, you don’t really need to worry about this one too much. Just know it exists. Because it’s such a short burst of energy, it uses something called adenosine triphosphate (ATP), which is made and stored in your muscle cells. As long as you’re getting enough calories and nutrients, you’ll have plenty of ATP available.