Which substance is considered a fuel for the ATP-CP energy system?

The ATP-CP energy system, also known as the phosphagen system, primarily relies on creatine phosphate (CP) as its key fuel source. This system is crucial for providing immediate energy for high-intensity activities lasting up to about 10 seconds, such as sprinting or heavy lifting. When the body requires quick bursts of energy, creatine phosphate donates its phosphate group to adenosine diphosphate (ADP), rapidly converting it back into adenosine triphosphate (ATP), the primary energy currency of the cell.

In contrast, other substances listed, such as glycogen, glucose, and fatty acids, are involved in different energy systems. Glycogen and glucose are primarily used in the glycolytic and oxidative systems, which are utilized for longer-duration activities. Fatty acids serve as fuel primarily during prolonged, lower-intensity exercise through aerobic metabolism. Therefore, creatine phosphate is uniquely matched to the ATP-CP energy system's needs for quick, powerful bursts of energy.