Lactic acid is an organic compound with the formula CH3CH(OH)CO2H. It is a white, water-soluble solid or clear liquid that is produced both naturally and synthetically. With a hydroxyl group adjacent to the carboxyl group, lactic acid is classified as an alpha hydroxy acid (AHA). In the form of its conjugate base called lactate, it plays a role in several biochemical processes.

In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal, which is governed by a number of factors, including monocarboxylate transporters, concentration and isoform of LDH, and oxidative capacity of tissues. The concentration of blood lactate is usually 1–2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion and as high as 25 mmol/L afterward

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