What is the role of lactate in physical activity?

Question

What will be an ideal response?

Answer 1

After the first 10 seconds or so of intense activity, energy from the phosphagen system diminishes, so muscle cells call upon the lactic acid system to produce more ATP. The lactic acid system involves the anaerobic breakdown of glucose to pyruvate (and then of pyruvate to lactate). The primary source of glucose is muscle glycogen. This system can generate a small amount of ATP quickly for high-intensity activity lasting up to 3 minutes.

When the rate of glycolysis exceeds the capacity of the mitochondria to accept hydrogens with their electrons for the electron transport chain, the accumulating pyruvate molecules are converted to lactate. Lactate is the product of anaerobic glycolysis. At low intensities, lactate is readily cleared from the blood, but at higher intensities, lactate accumulates. When the rate of lactate production exceeds the rate of clearance, intense activity can be maintained for only 1 to 3 minutes (as in a 400- to 800-meter race or a boxing match). Lactate has long been blamed for muscle fatigue, but research disputes this idea. Working muscles may produce lactate and experience fatigue, but the lactate does not cause the fatigue.

Lactate quickly leaves the muscles and travels in the blood to the liver. There, liver enzymes convert the lactate back into glucose. Glucose can then return to the muscles to fuel additional activity. The recycling process that regenerates glucose from lactate is known as the Cori cycle.