It is an enzyme-mediated multi-step process, where the glucose is partially oxidized to two molecules of pyruvate.
It occurs in the cytoplasm. It is the first step in cellular respiration.
During lactic acid fermentation, the pyruvic acid is reduced to lactic acid by lactate dehydrogenase in the absence of oxygen.
NADH is then oxidized to NAD+ in the said process. Lactic acid fermentation then takes place in muscles during strenuous exercise when oxygen is inadequate to derive the energy through oxidative phosphorylation.
