Amino Acids Metabolism and Central Fatigue in Prolonged Exercise

Journal of Exercise Nutrition & Biochemistry 1997;1(1):7-28.

Abstract

Protein generally has not been regarded as a significant source of energy during prolonged exercise, and then protein metabolism has received relatively little attention in comparison to carbohydrate and fat metabolism. During prolonged exercise, however, there is an increase in the rate of net protein breakdown in skeletal muscle. It has been hypothesized that an increase in the plasma free tryptophan/BCAA concentration ratio during prolonged exercise is cause of central fatigue due to increased uptake of tryptophan in the brain and increased synthesis of serotonin. The increased rate of utilization of BCAA by muscle is reduced to its plasma concentration during prolonged exercise leading to glycogen depletion. Therefore, it is reasonable to assume that supplementation with BCAA can inhibite an increase in the plasma concentration ratio of free tryptophan/BCAA and improve endurance performance. Though supplementation with BCAA reduce the concentration of brain tryptophan, it can not be improved endurance performance. Because BCAA may lead to drain 2-oxoglutarate by the BCAA aminotransferase reaction, a reduced flux in the citric acid cycle and a limiting of aerobic oxidation of the available fuels. Moreover, BCAA may also lead to accumulation of ammonia. In conclusion, versatile researches to reduce central fatigue and improve endurance performance in prolonged exercise are required.