Certified Personal Trainer (NSCA) Practice Exam 2025 – Complete Prep Guide

The aerobic system is the correct choice because it primarily relies on the presence of oxygen to metabolize carbohydrates and fats for energy, especially during extended physical activity. This energy system becomes dominant during activities that last longer than a few minutes, such as running, cycling, or swimming at a steady pace.

In this system, carbohydrates are broken down through glycolysis into glucose, which is then further processed in the presence of oxygen to produce ATP (adenosine triphosphate), the energy currency of the cell. Similarly, fats are oxidized to release energy, providing a substantial amount of ATP during prolonged, lower-intensity activity. As the duration of exercise increases, the contribution from fat oxidation becomes more significant, making it a highly efficient energy source during endurance events.

The alternative options pertain to different energy systems that serve different functions. The phosphagen system, for instance, is utilized for short bursts of high-intensity activity lasting about 10 seconds and relies exclusively on stored ATP and creatine phosphate. The glycolytic system uses carbohydrates as well but primarily supports high-intensity efforts lasting up to several minutes by generating energy anaerobically, which leads to the accumulation of lactic acid. The intramuscular system is not defined as a specific