Leucine, isoleucine, and valine are essential amino acids and are collectively termed the branched-chain amino acids (BCAAs). BCAAs comprise approximately one-third of muscle protein, and of these three amino acids, leucine has been researched the most extensively. Significant decreases in plasma or serum levels of leucine 01-33%) have been shown to occur after aerobic exercise. Exercise has also been shown to increase the tryptophan/BCAA ratio, which has been touted as support for the central fatigue hypothesis. This hypothesis suggests that an increase in the uptake of tryptophan by the brain will cause an increase in the release of serotonin. This release will ultimately impair endurance performance.

Human Studies

In a study by Blomstrand et al. BCAAs or a placebo were given to subjects during a 30-km cross-country race or a marathon (42.2 km). The subjects who ran the marathon in 3.05-3.30 hours had a significant improvement in their running time, whereas the faster runners (less than 3.05 hours) showed no improvement in their performance. However, if subjects were grouped together, no significant differences in performance were noted.

Another study by Blomstrand et al. had five male endurance-trained subjects cycle at 75% VO2 max until exhaustion. During exercise, the subjects were randomly given a 6% carbohydrate solution with or without 7 g/L of BCAAs or a flavored water solution (placebo). Performance decreased in four out of the five subjects during the flavored water trial when compared with the two carbohydrate periods. However, no differences in performance were seen between the two carbohydrate groups.

In a similar study by van Hall et al. ten endurance­trained males cycled at 70-75% of their maximum power output and randomly ingested a 6% sucrose solution (control) or a 6% sucrose solution with 3 g/L of tryptophan, 6 g/L of BCAAs, or 18 g/L of BCAAs. Exercise time to exhaustion was not different between the groups.

Moreover, a study by Struder et al. was conducted with ten male subjects. These subjects were required to cycle until exhaustion during four different trials. Subjects ingested a placebo, 20 mg paroxetine, 21 g BCAAs, and 20 g tyrosine separately during the four trials. The results showed that exhaustion was reached earlier during the paroxetine trial, but there were no significant differences among the other trials. When nine well-trained cyclists ingested glucose, glucose plus BCAA, or a placebo, the results were similar. is No differences in performance times were noted in any of the groups after a 100-km cycling test.

Elderly men have also been used as subjects in BCAA studies. Seventeen men, with a mean age of 63 years, were given either BCAA 06, 2, and 2 g of leucine, isoleucine, and valine, respectively) or a placebo The subjects performed cycling at 75% of their maximum heart rate 1 hour per day, 4 days per week. Maximal oxygen uptake significantly increased by about 5%, but the increase also occurred in the placebo group.

However, when BCAAs were given to subjects in the heat, the results were quite different. Six women and seven men rested in the heat (-34°C) before cycling at 40% of their VO2max until exhaustion. The subjects performed this routine twice while ingesting 5 mL/kg of either a placebo or BCAA drink every 30 minutes. The subjects’ times to exhaustion increased significantly during the BCAA trial.

With a decreased concentration of leucine after aerobic exercise, it would seem probable that the ingestion of supplemental BCAA would increase endurance performance. However, the preponderance of studies shows no effect of BCAA supplementation.

Posted in Creatine | No Comments »