Lactate produced during anaerobic respiration does not stay in the muscle. It diffuses into the blood and is carried to the liver.In liver cells, lactate is oxidised back to pyruvate by lactate dehydrogenase, and NAD is reduced in the process. The pyruvate can then be:
• oxidised completely to carbon dioxide and water through the link reaction, Krebs cycle and oxidative phosphorylation, releasing the energy that was left in the lactate; or
• converted into glucose, which can be released into the blood or stored as glycogen.This needs oxygen, which is why breathing rate and heart rate stay high after exercise has stopped. The extra oxygen taken in after exercise, above resting needs, is called the oxygen debt. It is used to oxidise lactate and to restore the ATP, creatine phosphate and oxygen stores of the muscles.
So lactate is not simply a waste product: it still contains useful energy and can be converted back. This is different from the ethanol made by yeast, which cannot be converted back to pyruvate.If lactic acid builds up faster than it is removed, it releases hydrogen ions and lowers the pH of the muscle tissue. This can inhibit enzymes, including those of glycolysis and muscle contraction, and contributes to muscle fatigue. Training improves the removal of lactate, so athletes can work harder before fatigue sets in.
• oxidised completely to carbon dioxide and water through the link reaction, Krebs cycle and oxidative phosphorylation, releasing the energy that was left in the lactate; or
• converted into glucose, which can be released into the blood or stored as glycogen.This needs oxygen, which is why breathing rate and heart rate stay high after exercise has stopped. The extra oxygen taken in after exercise, above resting needs, is called the oxygen debt. It is used to oxidise lactate and to restore the ATP, creatine phosphate and oxygen stores of the muscles.
So lactate is not simply a waste product: it still contains useful energy and can be converted back. This is different from the ethanol made by yeast, which cannot be converted back to pyruvate.If lactic acid builds up faster than it is removed, it releases hydrogen ions and lowers the pH of the muscle tissue. This can inhibit enzymes, including those of glycolysis and muscle contraction, and contributes to muscle fatigue. Training improves the removal of lactate, so athletes can work harder before fatigue sets in.