Effect of branched-chain amino acid supplementation on mental performance.

Several studies have indicated that physical exercise influences the synthesis and metabolism of brain monoamines, particularly 5-hydroxytryptamine (5-HT) (see Chaouloff 1989). An increase in the synthesis and concentration of 5-HT in the brain is suggested to contribute to the feeling of fatigue during sustained exercise (Blomstrand et al. 1988, 1989). In these latter studies it was shown that the plasma concentration ratio of free tryptophan/other large neutral amino acids (LNAA) increased during exercise in both human subjects and rats