The study assessed the effects of BCAA supplementation on young active males performing a constant load exercise (CLE).
“These findings show the importance of BCAA supplementation in exercise physiology in humans and provide evidence to support more diverse nutritional strategies during exercise,” wrote researchers from Beijing Sport University and other institutions in China and Sweden.
BCAAs in exercise and fatigue
BCAAs are commonly used to promote muscle synthesis, but their effects on substrate metabolism during exercise aren’t as clear.
The primary metabolic substrates are carbohydrates and fats. Enhancing fat oxidation is a strategy to reduce glycogen depletion and prolong exercise duration by avoiding fatigue.
However, previous studies have shown that a low-carbohydrate, high-fat diet may impair exercise metabolism and performance, so alternative ways to enhance fat oxidation are of interest.
Discussing the results, the researchers wrote, “The intake of BCAA most likely enhances fat oxidation during CLE, preserves glycogen levels in the body, and thus increases CHO oxidation during subsequent TTE.”
Central fatigue can occur during exercise due to ammonia accumulation in the blood and an increase in serotonin, which induces a feeling of tiredness during exhaustive exercise.
BCAAs may reduce cerebral serotonin synthesis and can compete with tryptophan to cross the blood-brain barrier. Therefore, they “are potent in mitigating central fatigue during high-intensity exercise,” note the researchers.
“We suppose that a lack of BCAA supply during acute exercise leads to quick glycogen depletion and an increase in protein consumption for energy, eventually elevating blood ammonia,” they wrote.
“Moreover, as blood ammonia easily crosses the blood–brain barrier, this increase directly boosts the brain’s uptake of ammonia. It likely alters the brain’s energy metabolism and intraneuronal signaling pathways and causes central fatigue. Therefore, our findings, together with previous data, demonstrate that BCAAs play a role in alleviating central fatigue.”
Study details
Eleven active males, with an average age of 21, participated in the double-blind, placebo-controlled, cross-over study.
They completed one hour of cycling constant load exercise (CLE) at 60% VO2max power, followed by a time-to-exhaustion (TTE) test at 80% VO2max power after supplementation with BCAAs or placebo for three consecutive days.
Results revealed significant improvements in the supplement group’s fat oxidation rate after 20 and 30 minutes of CLE compared to placebo and in the cycling efficiency during TTE.
The participants’ perceived level of muscle soreness, measured using visual analogue scale (VAS) scores, significantly decreased post-exercise in the BCAA group. Blood ammonia and insulin were also lower in the supplement group post-exercise.
The researchers recognize the lack of muscle biopsies as a limitation of the study, which could have shown changes in muscle glycogen. They call for further research to explore the effects of BCAAs and different nutritional supplements on exercise performance.
Source: Nutrients 2025, 17(7), 1290; https://doi.org/10.3390/nu17071290 ; “Branched-Chain Amino Acid Supplementation Enhances Substrate Metabolism, Exercise Efficiency and Reduces Post-Exercise Fatigue in Active Young Males.” Authors: C. Luan