Journal Title (Medline/Pubmed accepted abbreviation): Eur. J. Clin. Nutr.
Page numbers: 1166-1171
doi (if applicable): 10.1038/ejcn.2010.149
Background: During exercise, ammonia (NH4+) resulting from protein oxidation can accumulate in the muscle and, among other factors, is a potential cause muscle fatigue. Ammonia and lactic acid disrupt pH homeostasis in the muscle and ammonia can consume inosinic acid that is used to make ATP. Ammonia is cleared from the body via the urea cycle in the liver. Ornithine is a key amino acid for the proper function of the urea cycle. As such, it might be proposed that ornithine supplementation could increase clearance of ammonia via increased activity of the urea cycle. This increased ammonia clearance, in turn, could have the potential to improve performance.
Hypothesis/Research Question: Does L-ornithine supplementation increase performance during aerobic exercise? Does L-ornithine supplementation increase the rate of recovery from fatigue?
Subjects: 14 healthy trained males (moderate-high intensity exercise at least 3 times per week, over 2 hrs per session), age 22.2 ± 1.0 yrs old
Experimental design: Randomized, balanced, double-blind, cross-over, placebo controlled study
Treatments and protocol:
L-ornithine supplement: Aqueous solution of 0.1 g/kg body weight L-ornithine hydrochloride (7.25 ± 1.25 g/dose) + flavor
Placebo: Aqueous solution of 0.1 g/kg body weight indigestible dextrin + the same flavor
Baseline blood samples were drawn and then beverages were ingested. After 1 hr of rest, a second blood sample was acquired and incremental exhaustive ergometer bicycle exercise commenced. Participants cycled about 60 rpm. Resistance started at 0 W for 3 min. Then, exercise load was increased every min until subjects could not maintain a cadence of 40 rpm. (The rate of increase was calculated on an individual basis based on peak oxygen consumption, height, and age.) During cycling, oxygen consumption and expired gases as well as heart rate were continuously monitored. At exhaustion, a third blood sample was collected and the subjects rested for 15 min. A fourth blood draw was performed. Blood was analyzed for ornithine, ammonia, urea, lactic acid, and glutamate. Performance measures included time to exhaustion, maximum heart rate, exercise intensity, and maximal oxygen consumption.
L-ornithine is able to reduce ammonia levels both during and after exercise but these doses (0.1 g/kg body weight) were not successful in improving performance. It is possible that this supplement could function synergistically with other supplements, perhaps lactic acid buffers, to improve performance and increase time to exhaustion. This possibility has yet to be explored.