Question

explain the increase in blood lactate which occurs above 50-60% Vo2max? Blood lactate is the buffered form of lactic acid derived from cellular anaerobic glycolysis. (HINT: connect motor unit recruitment order with collective metabolism).

Answer 1

A physiological measurement to consider in endurance events is the Blood lactate concentration.This is produced during anaerobic glycolysis and most of it is used up during the exercise by the working muscles.When we recover after exercise most of blood lactate is removed from the blood by liver.But sometimes the production of lactate may exceed a threshold value and tissues may not be able to remove it from the blood.This is called Lactate Threshold.In general this threshold is expressed as Vo2max in percentage.Vo2 max or Maximal oxygen uptake is the maximum rate of consumption of oxygen during exercise or any sport.Generally it is about 50-60% and for athletes it is 75%.
During exercise at low levels of intensity slow twitch motor unit muscles are used to carry workload of exercise.This muscles have high aerobic endurance.When the intensity of exercise is increasing then recruited slow twitch muscles are shifted to recruit of fast twitch motor unit.These muscles have an enhanced anaerobic endurance.This shifts the energy intake from mitochondrial respiration of slow twitch muscles to glycolysis of fast twitch muscles.During glycolysis pyruvate is formed as an end product.This pyruvate cannot enter the mitochondria for further breakdown.At higher intensities vo2max is reached and metabolism is shifted to anerobic instead of aerobic and the pyruvate is converted to lactate and is used for muscle activities and in liver.

Pyruvate (C3H4O3) + NADH + H+ ⇄ lactic acid (C3H6O3) + NAD+