Which energy system provides immediate energy for very short, high-intensity efforts and relies on stored phosphates?

• A. Anaerobic glycolysis
• B. Phosphagen system (ATP-CP)
• C. Aerobic respiration
• D. Lipid oxidation

Answer: (B)

This question targets understanding which energy system kicks in right away for very short, all-out efforts and uses stored phosphates. The phosphagen system, also called the ATP-CP system, does this by rapidly regenerating ATP from ADP using phosphocreatine stored in muscles. Because it relies on these immediate phosphate reserves and does not require oxygen, it can power maximal contractions for a brief moment—roughly a few seconds—until the phosphocreatine is depleted and other energy pathways must take over.

The other systems aren’t about immediate energy from stored phosphates: anaerobic glycolysis uses glucose and can ramp up quickly but needs a short delay and produces lactate as a byproduct; aerobic respiration requires oxygen and sustains activity much longer at a lower rate; lipid oxidation is slow and supports long-duration, lower-intensity efforts.