CSSD Practice Exam 2026 – Complete Study Resource

During intense exercise, the body requires a rapid supply of energy to sustain performance, often surpassing the available oxygen supply. This leads to anaerobic glycolysis, a metabolic pathway that produces energy without the need for oxygen.

In anaerobic glycolysis, glucose is broken down to produce ATP (adenosine triphosphate), the energy currency of cells. As this process occurs under low oxygen conditions, pyruvate is produced but cannot enter the mitochondria for aerobic respiration. Instead, it is converted into lactic acid. This conversion serves to regenerate NAD+, an essential coenzyme that allows glycolysis to continue producing ATP despite the lack of oxygen.

This mechanism explains the accumulation of lactic acid during high-intensity exercise. The build-up of lactic acid can contribute to muscle fatigue and discomfort, indicating the prevalence of anaerobic metabolism in these conditions. In contrast, aerobic glycolysis involves the use of oxygen, fat oxidation primarily refers to breaking down fatty acids for energy, and oxidative phosphorylation occurs in the presence of oxygen within the mitochondria, making them unsuited to the scenario of intense exercise characterized by lactic acid production.