During strenuous exercise, muscle cells may shift from aerobic respiration to lactic acid fermentation when oxygen becomes limited. What is the primary metabolic purpose of fermentation in these cells?

Core Concept

During glycolysis, NAD+ is reduced to NADH. Under aerobic conditions, NADH donates electrons to the electron transport chain, regenerating NAD+. Without oxygen, this pathway is blocked. Lactic acid fermentation converts pyruvate to lactate while oxidizing NADH back to NAD+, which is essential for glycolysis to continue operating.