Which energy system produces energy in the absence of oxygen?

The anaerobic energy system is responsible for producing energy in the absence of oxygen. This system is essential for short bursts of high-intensity activities, such as sprinting or heavy lifting, where the demand for energy exceeds the oxygen supply. The body relies on stored energy substrates like phosphocreatine and glycogen to quickly regenerate adenosine triphosphate (ATP), the energy currency of the cell, without requiring oxygen.

In contrast, the aerobic energy system uses oxygen to produce ATP, primarily during lower-intensity, longer-duration activities. The cardiovascular system relates more to the body's ability to transport oxygen and nutrients to tissues, while endurance refers to the ability to sustain prolonged physical activity, often relying on the aerobic system for energy. Thus, identifying the anaerobic system as the energy source utilized in the absence of oxygen is essential for understanding how the body responds to different intensities of exercise.