About lactic acid in the human body

Lactic acid is naturally present in humans, as well as in animals. It is well known that it is formed from glycogen by muscle cells when the oxygen supply is inadequate to support energy production.
There are many misconceptions about lactic acid and lactate in the body. Lactate was long considered one of the causes of both fatigue during exercise and the stiffness felt after. However, on the contrary, lactate is actually an important fuel used by the muscles during prolonged exercise, since lactate produced in one muscle can be oxidized in another muscle. So, rather than causing fatigue, lactic acid and lactate help delay the onset of fatigue and improve sport performance.