AFAA Personal Trainer Certification Practice Exam

Which energy system primarily utilizes glucose, fat, and protein for fuel?

1. Aerobic system

2. Anaerobic system

3. Phosphocreatine system

4. Lactic acid system

The correct answer is: Aerobic system

The aerobic system is the correct choice because it is primarily responsible for generating energy through the oxidation of glucose, fat, and protein during prolonged, lower-intensity activities. This energy system uses oxygen to convert these macronutrients into adenosine triphosphate (ATP), which is the body’s primary energy currency. The aerobic system is efficient for long-duration activities because it can sustain energy production as long as there are adequate oxygen and fuel sources available. During this process, carbohydrates, fats, and, to a lesser extent, proteins serve as fuel. Fat, for example, is particularly important during longer exercise sessions, while carbohydrates provide faster energy for moderate to high-intensity efforts. In contrast, the anaerobic system relies primarily on the breakdown of glucose without the use of oxygen, which occurs during short, high-intensity activities. The phosphocreatine system is used for very rapid bursts of energy and lasts only a few seconds, while the lactic acid system is involved in processes that produce lactate during higher-intensity efforts when oxygen is scarce. None of these systems utilize fat or protein in the same way the aerobic system does, making the aerobic system the primary energy pathway for the utilization of glucose, fat, and protein for fuel