Effects of Branched-Chain Amino Acid Supplementation on the Exercise Time to Exhaustion in Sedentary Individuals

PURPOSE: The purpose of the present investigation was to examine the effects of Branched-chain amino acid (BCAA) administration on the exercise time to exhaustion in sedentary individuals. The central fatigue hypothesis proposes that, by maintaining a favourable plasma free Tryptophan (TRP) to BCAA ratio, BCAA supplementation may have the ability to reduce the rate of entry of TRP into certain areas of the brain. TRP is the metabolic pre-cursor of serotonin. Serotonin is a chemical neurotransmitter, which appears to have a role to play in the control of lethargy, tiredness and sleep. It has been suggested that reductions in TRP concentrations in the brain will decrease brain serotonin synthesis which may help to delay the onset of this form of fatigue, known as central fatigue. METHODS: Ten, healthy, non-obese and non-active males aged between 18 and 25 participated in the study. Each participant performed two submaximal exercise bouts until volitional fatigue, while receiving either a BCAA supplement (50% leucine,30% valine, 20% isoleucine) or a placebo (PLAC). Cardiorespiratory measures of VO2 (ml.kg.min, VCO2 (l/min), Ve (l/min), RER and heart rate (bpm) were recorded throughout. RPE values were taken during each trial. Post-exercise cognitive assessments of reaction time, memory recall and attention capacity were performed following each treatment. RESULTS: Exercise time to exhaustion was significantly longer during the BCAA (96.02 + 15 mins) trial when compared to the PLAC (86 + 14 mins) trial (P<0.05). No significant differences in any of the cardiorespiratory measures were observed between trials or at exhaustion. No significant differences in RPE were found between treatments. Post-exercise memory recall demonstrated no observable differences between trials. Following the BCAA trial simple reaction time scores were significantly faster than the PLAC trial (210 + 40msec v's 226 + 37msecs) (P<0.05). Participants concentration levels were improved following the BCAA trial as evidenced by a significantly lower recorded error score in a paper and pencil cancellation test (1.3 + 1.3 v's 4.7 + 3.1) (P<0.05). CONCLUSIONS: The present investigation demonstrated that supplementation of BCAA during prolonged submaximal exhaustive exercise resulted in a significantly longer exercise duration in a sedentary population. Although it cannot be firmly concluded that the BCAA administered were not utilised for metabolic purposes by skeletal muscle, improvements in post-exercise cognitive performance tend to suggest that the BCAA administered had a role to play in offsetting feelings of fatigue and tiredness experienced by a sedentary population and that this fatigue may be of central origin.