Leucine

Leucine is an essential branched-chain amino acid (BCAA) and the principal nutrient activator of the mTORC1 pathway driving post-exercise muscle protein synthesis, as well as a competitor with tryptophan for brain uptake relevant to central fatigue. Salivary leucine reflects BCAA availability and the anabolic and fatigue-modulating amino-acid balance around training. Blomstrand et al. (1991) demonstrated that BCAA provision during sustained exercise alters plasma amino-acid profiles and the central fatigue response.