L-Ornithine: Arginine's Overlooked Metabolic Child

Molecular structure of l-ornithine
(HMDB. V2.5)

Ornithine is an amino acid produced in the urea cycle by the splitting off of urea from arginine. It is a central part of the urea cycle, which allows for the disposal of excess nitrogen. L-Ornithine is also a precursor of citrulline and arginine BUT hardly any of the self-proclaimed supplement gurus know about its proven effects on exercise performance.

Almost two years ago, Sugino et.al. (Sugino. 2008) published the results of a study which investigated the effect of 2mg or 6mg l-ornithine supplementation on 120min exercise performance on a cycle ergometer and found that

oral L-ornithine administration promoted lipid metabolism and activated the urea cycle from serum triacylglycerol, ketone bodies, free fatty acids, and blood ammonia level changing. L-ornithine significantly attenuated the subjective feeling of fatigue (measured by visual analog scale at postrecovery) compared with postload (P < .01). [...] In the physical performance test in female subjects, the decrease in mean speed for 10 seconds maximum pedaling from 0.5- to 3.5-hour trials in the group receiving L-ornithine was smaller than that in the group receiving placebo (P < .05). (Sugino. 2008)

The scientists explain their observations by a supplement-induced increase in the "efficiency of energy consumption" and an increased rate of ammonia-excretion.
In his Amino Acid "Bible" Mauro Di Pasquale writes about l-ornithine:

Ornithine has many similarities with its parent amino acid, arginine. Both are dibasic amino acids, both are involved in the urea cycle, and both have effects on insulin, glucagon, and GH secretion and release. Unlike arginine, however, ornithine is not used for protein synthesis. Ornithine may help increase GH secretion in high doses. 

In one study, 12 bodybuilders were given three different doses of ornithine on successive weekends. Half of the bodybuilders responded to the highest dose (170 mg=kg) with significant increases in GH. Ornithine had no effect on serum insulin levels. 

As explained earlier, ornithine is involved in the urea cycle and thus may have some effect in reducing exercise-induced increased ammonia levels and thus possibly decreasing fatigue. Ornithine is also involved in polyamine synthesis. Polyamines are important regulators of cellgrowth. (Di Pasquale. 2008. 307)

So, if you had asked the real experts, they would have well been able to explain you why there is l-ornithine in many of the better pre-workout-formulas on the market.