Effects of BCAA Supplementation on Plasma Amino Acids and on Subjective Fatigue and Muscle Soreness during Low-Intensity Prolonged Exercise

Abstract

An increased concentration of plasma tryptophan (Trp) may increase serotoninergic activity in the brain, possibly leading to central fatigue during prolonged exercise. Supplementation branched-chain amino acids (BCAA) may prevent Trp uptake into the brain. However there are few reports concerning the effects of BCAA on physiological and psychological responses during low-intensity prolonged exercise. PURPOSE: The purpose of this study was to investigate the effects of BCAA supplementation on plasma amino acids, in particular the plasma free Trp concentration, and on subjective fatigue and muscle soreness during low-intensity prolonged exercise. METHODS: Eight healthy untrained male subjects who were 30 – 48 yrs with a body mass of 70.0 +/− 8.0 kg (mean +/− S.D.), height of 173.2 +/− 5.9 cm and a maximal oxygen uptake of 40.0 +/− 5.9 ml/kg/min performed 4 h (or until exhaustion) of cycling at 50 % VO max on two separate occasions, at least four weeks apart. During exercise, the subjects ingested either a 50-ml solution of BCAA (8 g/l) or flavored water (placebo) every 12 min. Blood samples were drawn before exercise, every 30 min during exercise, immediately post-exercise, and at 30 min and 4 hr during the recovery period. Samples were analyzed for plasma Trp and BCAA concentration. Subjective fatigue and muscle soreness were measured by the visual analog scale (10 cm) before exercise, after 2 h of exercise, immediately post-exercise, and 4 hr, 1 day and 2 day after the completion of exercise. HR and rectal temperature were recorded throughout the exercise. RESULTS: Exercise time was not different between the BCAA and the placebo trials. Plasma free Trp concentration decreased progressively during both trials. In the BCAA trial, plasma Trp concentration was significantly lower than the placebo trial at 90 min and 150 min (p <0.01). In the placebo trial, there was no change in plasma BCAA concentration, whereas plasma BCAA concentration was immediately increased in the BCAA trial (p <0.001). Therefore BCAA ingestion resulted in a significant reduction in the ratio of free Trp/BCAA during exercise. The rating of subjective fatigue significantly increased after 2 h of exercise, immediately post-exercise, and 4 hr after the completion of exercise in both trails. However, in the BCAA trial, the rating of subjective fatigue was lower than the placebo trial. CONCLUSION: The results of this study suggest that BCAA supplementation might suppress changes in the concentration of plasma free Trp and subjective fatigue during low-intensity prolonged exercise.