Lactic acid fermentation

Lactic acid fermentation is a form of anaerobic respiration that has a glucose-consuming catabolic pathway and is used by both bacteria and animals to produce ATP in the absence of oxygen. Lactic acid fermentation breaks down a glucose molecule into two molecules of lactate, which combines with hydrogen ions to form lactic acid. The energy released is stored in two ATP molecules and several NADH molecules. However, since there is no oxygen available to run the electron transfer chain, the energy of NADH cannot be transferred to ATP. Lactic acid fermentation is far inferior to cellular respiration as a way of generating energy, but muscle cells do use it during heavy exertion. The resulting buildup of lactic acid may have a role in muscle cramps.