Certified Personal Trainer (NSCA) Practice Exam 2026 – Complete Prep Guide

The correct answer identifies the three primary energy systems that the body utilizes during various intensities and durations of physical activity: the ATP-PC system, the glycolytic system, and the oxidative system.

The ATP-PC system, also known as the phosphagen system, is the first energy pathway that the body taps into during high-intensity, short-duration activities, such as sprinting or heavy lifting. It relies on stored ATP and phosphocreatine in the muscle cells, allowing for immediate energy release without the need for oxygen. This system can sustain activity for about 10 seconds before fatigue sets in.

Following the ATP-PC system, the glycolytic system kicks in for moderate to high-intensity efforts lasting from about 10 seconds to 2 minutes. It involves the breakdown of glucose through anaerobic glycolysis to produce ATP, leading to the formation of lactate. This system allows for a quick supply of energy when the phosphagen system is depleted but does not use oxygen, resulting in potential lactate accumulation and fatigue.

Finally, the oxidative system becomes predominant during lower intensity, long-duration activities, such as distance running or cycling. This system employs oxygen to metabolize carbohydrates, fats, and, to a lesser extent, proteins to produce ATP. It