l-Ornithine supplementation attenuates physical fatigue in healthy volunteers by modulating lipid and amino acid metabolism

We examined the effects of l-ornithine administration on physical fatigue. In a double-blind, placebo-controlled, 2-way crossover study, 17 healthy volunteers were randomized to l-ornithine (2000 mg/d for 7 days and 6000 mg/d for 1 day as l-ornithine hydrochloride) or placebo for 8 days. The fatigue-inducing physical task consisted of workload trials on a cycle ergometer at fixed workloads for 2 hours on 2 occasions. We 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). Moreover, in female subjects, the subjective feeling of fatigue was significantly lower compared with the placebo group (P < .05). 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). These results suggest that l-ornithine has an antifatigue effect by increasing the efficiency of energy consumption and promoting the excretion of ammonia. l-ornithine is a free amino acid and is not rich in meats or fish, so it is difficult to obtain amounts of l-ornithine from ordinary meals that would be sufficient to promote the antifatigue effect. We recommend l-ornithine intake as a nutritional supplement in cases of physical fatigue.