During various types of exercise, the body utilizes different energy sources based on intensity and duration. Initially, it relies on ATP (adenosine triphosphate) for quick bursts of energy, sourced from stored energy in muscles. For activities lasting longer than a few seconds, the body shifts to glycogen (stored carbohydrate), breaking it down for glucose. In endurance exercises, such as long-distance running, the body can further adapt by burning fat as a primary energy source, which provides a more sustainable fuel source. Each energy source has a role in optimizing performance based on the type and length of activity.