Amino acids and central fatigue.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing preclinical mechanisms and human exercise studies
PubMed 11310928 · doi:10.1007/s007260170063
What was done
This narrative review summarizes animal and human studies exploring the mechanisms of central fatigue during sustained exercise, focusing on brain 5-hydroxytryptamine (5-HT) synthesis, plasma free tryptophan/BCAA ratios, and the effect of oral BCAA supplementation on mental and physical performance.
What was found
The abstract provides no numerical data or effect sizes. Qualitatively, physical exercise increases the plasma free tryptophan/BCAA ratio, facilitating tryptophan entry into the brain and stimulating 5-HT synthesis. Pharmacologically elevating 5-HT impaired exercise performance in rats and humans, while reducing 5-HT improved running performance in rats. In humans, BCAA ingestion during heavy sustained exercise reduced perceived exertion and mental fatigue, improved post-exercise cognitive performance, and showed potential physical performance benefits in hot environments or competitive races.
Why it matters
It outlines the central fatigue hypothesis linking amino acid transport dynamics across the blood-brain barrier to neurotransmitter synthesis, establishing a rationale for BCAA supplementation during prolonged exertion.
Limits
This is a narrative review with no systematic search methodology, sample sizes, or quantitative data reported in the abstract. Key findings rely partially on animal models and pharmacological manipulations, and the abstract notes that further experiments are required to clarify physical performance outcomes.
Cited by
- supports Exercise causes branched-chain amino acids to be taken up into muscle cells, reducing competition for tryptophan transport across the blood-brain barrier.