National Academy of Sports Medicine (NASM) Group Fitness Instructor Practice Exam

Which metabolic energy system utilizes glucose to create energy without the presence of oxygen?

1. Aerobic glycolysis

2. Phosphagen system

3. Anaerobic glycolysis

4. Lactic acid system

The correct answer is: Anaerobic glycolysis

Anaerobic glycolysis is the correct answer because it refers specifically to the breakdown of glucose to produce energy when oxygen is not available. This metabolic pathway is essential during high-intensity activities where the body's demand for energy exceeds the supply of oxygen available for aerobic metabolism. During anaerobic glycolysis, glucose is converted into pyruvate, which is then transformed into lactic acid in the absence of oxygen. This process allows for the quick generation of energy, making it critical during short bursts of intense exercise, such as sprinting or heavy lifting. In contrast, aerobic glycolysis requires the presence of oxygen to fully metabolize glucose into energy, thus producing far more ATP (adenosine triphosphate) — the body's energy currency — compared to anaerobic glycolysis. The phosphagen system, on the other hand, utilizes stored creatine phosphate for immediate energy but does not use glucose directly. The lactic acid system is often used interchangeably with anaerobic glycolysis but primarily refers to the byproduct of aerobic glycolysis and the accumulation of lactic acid during high-intensity exercise.