The lactic acid that gets accumulated in the muscle cells during rigorous exercise causing muscle cramps is produced from

Lactic acid is produced from pyruvate during anaerobic respiration in muscle cells. During rigorous exercise, oxygen supply to muscle cells becomes insufficient to meet energy demands. Under these anaerobic conditions, glucose is broken down through glycolysis to produce pyruvate, which is then converted to lactic acid (lactate) by the enzyme lactate dehydrogenase. While glucose is the ultimate source, the direct precursor of lactic acid is pyruvate. The accumulation of lactic acid lowers the pH in muscle cells, contributing to muscle fatigue and cramps. ATP is the energy currency, not a precursor of lactic acid, and ethanol is produced in yeast fermentation, not in human muscles.