Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Tryptophan helps lift interval training to a higher level

Team sports players perform better in the field if they take a daily 600 mg of the amino acid tryptophan [structural formula shown here]. Sports scientists at the University of Barcelona came to this conclusion from experiments they did on sports-playing students.

Tryptophan & exercise

Discussions between physiologists on whether tryptophan enhances performance tend to end in deadlock. Things can get heated; the ergogenic effect of tryptophan is a minefield.

Tryptophan is a precursor of the neurotransmitter serotonin. If you have more serotonin in your brain than normal, you feel pleasanter. Your brain becomes less sensitive to pain and you will be less distracted by unpleasant thoughts and irrelevant information. So tryptophan supplementation can create a state of mind that also helps to improve sports performance.

Contradicting studies
In the 1980s this thought inspired researchers at the University of Barcelona to carry out an experiment with students who played sports. The students had to run at an intensity that was 80 percent of their maximal oxygen uptake. At this level of intensity you can no longer hold a conversation. When the subjects were given 600 mg tryptophan before running, they ran almost fifty percent longer than they did after they had been given a placebo.

In 1992 researchers at the Norwegian University of Sport and Physical Education repeated the experiment with a few modifications. They gave their subjects 1200 mg tryptophan, and got them to run at 100 percent of their maximal oxygen uptake. This had no effect at all. [Int J Sports Med. 1992 Aug;13(6):481-5.]

Dutch researchers in the mid-nineties also recorded no effect. They gave their subjects tryptophan not before but during their physical exertion. [J Physiol. 1995 Aug 1;486 (Pt 3):789-94.]

But the people who are most resistant to the idea that tryptophan may enhance sports performance are researchers who believe in the enhancing effect of BCAAs. These amino acids, according to a widely accepted theory, reduce fatigue during endurance exertion because they prevent tryptophan from entering the brain, thereby preventing it from being converted into serotonin. [Experientia. 1996 May 15;52(5):413-5.] [J Nutr. 2006 Jan;136(1 Suppl):274S-6S.] [J Nutr. 2006 Feb;136(2):544S-547S.]

The brain can only absorb a limited amount of amino acids, according to theory. During intensive physical exercise the muscles claim all amino acids from the blood except for tryptophan. As a result the brain absorbs more tryptophan and converts this into serotonin - and serotonin causes athletes to feel tired.

BCAA supplementation inhibits the brain's uptake of tryptophan, reduces fatigue and boosts endurance performance, whereas tryptophan supplementation only leads to negative effects, say BCAA supporters.

The Spanish researchers, who had demonstrated the performance enhancing effect of tryptophan in 1988, did another experiment a few years ago. The researchers got 20 sports-playing students aged 20-22 to do an hour-long interval training session on a cycle ergometer. The training session imitated the exertion pattern of team sports players during a match.

First the students cycled for 10 minutes at 50 percent of their VO2max. Then they cycled flat out for 30 seconds. The subjects had to repeat this cycle another three times. And finally the students cycled for another 20 minutes at 50 percent of their VO2max.

The researchers performed the test twice. On one occasion the students took 2 capsules containing 300 mg tryptophan for three days before the test and on the day of the test itself, so they took 600 mg tryptophan per day. On the day of the test the students took the tryptophan two hours before starting to cycle.

The supplement worked. The figure below shows that during half of the explosive 30-second sessions the tryptophan resulted in more average power and more peak power. Put simply, the athletes could pedal harder when they took tryptophan.

Tryptophan helps lift interval training to a higher level

Tryptophan helps lift interval training to a higher level

Tryptophan helps lift interval training to a higher level

Moreover, the subjects covered a greater distance in the last 20 minutes of the test when they'd taken tryptophan. The figure above shows this.

The researchers discovered that tryptophan supplementation reduced the increase in fatigue.

In the experiments where tryptophan did not have an effect it's possible that too high a dose of tryptophan was used, or that it was not given sufficiently in advance of the exertion. The researchers suggest that tryptophan is perhaps not only a precursor of serotonin, but also of related compounds that do not cause fatigue but may actually have a stimulatory effect.

"Oral L-tryptophan supplementation and the resulting increase in plasma tryptophan appear to influence physical performance in complex ways", the Spaniards conclude. "In several common cases, such as the present study, it is able to improve physical output, and it seems that fatigue induced by different test protocols may be mediated by different pathways."

Supplements manufacturer Recuperation Electrolitos funded the research.

Int J Neurosci. 2010 May;120(5):319-27.

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