Which energy system dominates 0-6 seconds of all-out effort?

• A. Glycolytic (lactic acid) system.
• B. Aerobic system.
• C. Phosphagen (ATP-PC) system provides immediate energy for very short, high-intensity efforts.
• D. Fat oxidation system.

Answer: (C)

The main idea this question tests is which energy system supplies energy fastest for very short, all-out efforts. For such immediate work, the phosphagen (ATP-PC) system is the key player because it uses stored ATP and phosphocreatine directly in the muscle to quickly regenerate ATP without any oxygen. Those stores enable maximal efforts right at the start, typically dominating the first few seconds, about 0–6 seconds. Once those immediate reserves are depleted, other systems begin to contribute: the glycolytic system takes over for slightly longer high-intensity bouts, the aerobic system handles sustained activity, and fat oxidation contributes mainly at lower intensities over longer durations. So the phosphagen system best fits the 0–6 second window because it provides instantaneous energy for ultra-short, high-intensity efforts.