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

During rigorous exercise, the demand for energy increases rapidly, often exceeding the oxygen supply available to muscle cells. Under these anaerobic conditions, the normal aerobic pathway is bypassed. Initially, glucose is broken down in the cytoplasm into a three-carbon molecule called pyruvate through glycolysis [2]. When oxygen is scarce, instead of entering the mitochondria for aerobic respiration, pyruvate is converted into lactic acid (lactate) [1]. This reaction is catalyzed by the enzyme lactate dehydrogenase and involves the oxidation of NADH to NAD+, which allows glycolysis to continue producing small amounts of ATP [1]. The accumulation of lactic acid in the muscle tissue is traditionally associated with the sensation of muscle cramps and fatigue during sudden or strenuous physical activity [2]. Once oxygen becomes available, lactate can be transported to the liver and reconverted into pyruvate [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.5 > p. 88
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.5 > p. 87