Lactate Tolerance, Diet, and Physical Fitness

Written by docteam Monday, 29 March 2010 10:15

It has been known since the work of A. V. Hill that lactate is generated during muscular work. This lactate diffuses down a twofold gradient into the blood and is carried to the liver and kidneys, where it is substrate for gluconeogenesis by the Cori cycle.

This arrangement illustrates the supportive role of the visceral organs during work. It also suggests that disposition of lactate may be one limit to work capacity. It can be shown that training allows larger work rates with lower levels of lactate production. Trained men show a quicker reduction to normal of blood lactate levels following the completion of work. In several mammals, including man, the rate of lactate production in the resting state is approximately 0.85 mg/kg/min.

During maximal exercise this can be increased at least fivefold. About three-fourths of this lactate is converted to carbon dioxide, and the rest appears as glucose. Only small amounts of lactic acid are excreted in the urine until the blood levels exceed 54 mg/ 100 ml. There is an increase of mitochondrial protein and augmentation of several oxidative enzymes. Krebs and his co-workers have shown with rats that either a low carbohydrate diet or preliminary exercise will increase the rate of gluconeogenesis in kidney tissue studied in vitro

The evidence thus suggest that the disposition of lactate generated by exercise is one limit of physical fitness.