Which energy system dominates during a 10–30 second high-intensity effort?

• A. Aerobic system
• B. ATP-PC (phosphagen) system
• C. Lactic acid system (anaerobic glycolysis)
• D. Fatty acid oxidation

Answer: (B)

The key idea is how quickly different energy systems can supply ATP to power a high-demand effort. The ATP-PC (phosphagen) system provides ATP extremely rapidly without needing oxygen, using stored phosphocreatine in the muscles. This fast, high-rate production is what powers maximal efforts at the start and remains the main source of energy for the early portion of a 10–30 second high-intensity effort. Even though phosphocreatine stores are limited and begin to run down, they still deliver the majority of ATP early in the task, with other systems (notably anaerobic glycolysis) stepping in as PC becomes depleted and the demand continues. The aerobic system is too slow to meet the rapid energy needs of this short, intense burst, and fatty acid oxidation is far too slow to contribute meaningfully in this time frame. So, the phosphagen system is the best match for dominating energy supply in this 10–30 second window.