Lactic acid is generated as a byproduct of anaerobic respiration, which occurs when glucose is metabolized for energy in the absence of sufficient oxygen.

In detail, anaerobic respiration takes place when oxygen levels are too low for aerobic respiration to occur. This situation is common during intense exercise, when the body’s demand for oxygen surpasses its availability. To meet energy needs under these conditions, cells transition to anaerobic respiration.

The process begins with glycolysis, where one molecule of glucose is broken down into two molecules of pyruvate. Glycolysis generates a small amount of energy and does not require oxygen. Under aerobic conditions, pyruvate would typically enter the mitochondria for further breakdown, yielding more energy. However, in anaerobic conditions, pyruvate is converted into lactic acid within the cytoplasm of the cell.

The formation of lactic acid is essential, as it enables glycolysis to continue by regenerating the coenzyme NAD⁺. This regeneration is critical because NAD⁺ is necessary for glycolysis to proceed, which is the sole pathway for energy production in anaerobic environments. Thus, the generation of lactic acid is a vital step in the anaerobic respiration pathway.

Nonetheless, lactic acid is not particularly beneficial for the body. It can accumulate and lead to muscle fatigue and discomfort. Once the period of intense exercise concludes and adequate oxygen becomes available, lactic acid is transported to the liver, where it is converted back into pyruvate and subsequently transformed into glucose through a process known as the Cori cycle. This conversion requires energy, which is why individuals continue to breathe heavily after exercising—to provide the oxygen necessary for the transformation of lactic acid back into glucose.