Which energy system is dominant after about 55 seconds of steady-state exercise?

• A. ATP-PCr
• B. Lactic acid
• C. Aerobic
• D. None

Answer: (C)

When exercise continues beyond the initial burst, energy production shifts toward aerobic metabolism. The ATP-PCr system is used up quickly, and anaerobic glycolysis can supply energy for a short period, but both are not sustainable for longer efforts. Around fifty-five seconds into steady-state exercise, the body relies primarily on the aerobic system, which uses oxygen in the mitochondria to oxides carbohydrates and fats to produce ATP. This slower but highly sustainable process matches the oxygen supply to the energy demand and allows continued work without the rapid lactate buildup seen with anaerobic pathways. So, the dominant energy system at that point is aerobic metabolism.