Which statement best describes energy system contributions during 20-second to 2-minute exercise?

Which statement best describes energy system contributions during 20-second to 2-minute exercise?

• A. The ATP-PC system dominates the entire 5-minute period.
• B. The oxidative system dominates the early seconds.
• C. The glycolytic system contributes heavily from about 10–20 seconds to 2 minutes.
• D. The phosphagen system is not involved in any high-intensity exercise.

Answer: (C)

During this 20-second to 2-minute window, energy is mainly supplied by anaerobic glycolysis. The phosphagen (ATP‑PC) system fires at the very start of high‑intensity effort, but its stores are exhausted within roughly 10 seconds, so it can’t sustain activity for 20 seconds to 2 minutes. The oxidative system ramps up more slowly and becomes the dominant source only as duration extends toward and beyond a couple of minutes, especially at lower to moderate intensities. So glycolysis shoulders the main workload in this middle range, providing rapid ATP production without requiring oxygen. The other statements misplace the timing or deny involvement of a system that still contributes early in high‑intensity efforts.

During this 20-second to 2-minute window, energy is mainly supplied by anaerobic glycolysis. The phosphagen (ATP‑PC) system fires at the very start of high‑intensity effort, but its stores are exhausted within roughly 10 seconds, so it can’t sustain activity for 20 seconds to 2 minutes. The oxidative system ramps up more slowly and becomes the dominant source only as duration extends toward and beyond a couple of minutes, especially at lower to moderate intensities. So glycolysis shoulders the main workload in this middle range, providing rapid ATP production without requiring oxygen. The other statements misplace the timing or deny involvement of a system that still contributes early in high‑intensity efforts.