Athletes who take a hefty dose of L-ornithine an hour before training get less tired. The amino acid stops the ammonia concentration in the blood from rising, write Japanese researchers in the European Journal of Clinical Nutrition.
Ornithine is released as proteins are broken down, and ornithine supplementation stimulates the activity of enzymes that help to clear up protein waste products. That's the reasoning behind sports supplements that contain L-arginine, L-ornithine [structural formula shown here] and L-citrulline: these amino acids are believed to help remove urea,
ammonia and also lactic acid from the bloodstream. And that's supposed to help boost athletes' performance.
The amino acids do much more in fact, but that's not what this article is about. The diagram below shows how citrulline, ornithine and arginine can be converted into each other in the body.
The Japanese gave 13 physically active students, average age 22, one gram of L-ornithine for every ten kg bodyweight. An hour later the students had to cycle on an ergometer. Every minute the researchers increased the speed, and the students had to continue cycling until they were no longer able to. The researchers then repeated the procedure, but gave the test subjects a placebo.
The supplement had no effect on the subjects' endurance capacity, but it did reduce the rise in ammonia concentration. The effect was statistically significant, but apparently in this experiment it was not enough to enhance performance.