Pardoxical: L-tryptophan Supplementation Increases Time to Exhaustion

Molecular structure of l-tryptophan
(HMDB v2.5)

In view of the generally accepted paradigm that BCAA supplementation exerts its beneficial effects on exercise performance partly via counteracting the rise of tryptophan levels (Castell. 1999) it appears highly counter-intuitive that L-tryptophan supplementation can decrease fatigue perception during an aerobic exercise with supramaximal intercalated anaerobic bouts in young healthy men (Javierre. 2010). Notwithstanding, Javierre et. al. found that supplementation of the serotonine precursor l-tryptophan increased time to exhaustion in consecutive submaximal exercise on a cycle ergometer at 50% of the participants respective VO2max for 10 min:

The total exercise time was 49.4% greater after receiving L-tryptophan than after receiving the placebo. A lower rate of perceived exertion was exhibited by the group while on tryptophan although the differences from the control group were not statistically significant. No differences were observed in the other parameters between the two trials.

The scientists conclude that the increase in serotonine lead to a concomitant increase in pain tolerance allowing the subjects who received l-tryptophan to cycle longer than the placebo-supplemented control group. If strength athletes and bodybuilders may benefit from l-tryptophan, as well, is however questionable. Exercising at 50% of ones VO2max is well-known to be a mind game. Weight lifting, on the other hand, is not so much about cumulating, but rather about immediate exhaustion; without corresponding research I will rather refrain from jumping into any conclusions.