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Nitric oxide (NO) is a gaseous substance that has a critical role in the body as a potent dilator of blood vessels.
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 It is well known that increasing the bioavailability of NO improves vasodilation and blood pressure, but emerging evidence suggests that nutritional manipulation of NO can improve other aspects of oxygen kinetics and even exercise performance. L-arginine is the rate limiting amino acid required for NO∙ synthesis.  Studies have shown that when large doses of arginine are ingested or infused directly into a blood vessel there is a positive effect on increasing vascular function. Building on this information, researchers from United Kingdom hypothesized that arginine supplementation would improve exercise efficiency and enhance performance. Healthy men performed an exercise test on a cycle on two occasions. During one trial they consumed 6 grams of arginine and during the other trial they consumed a placebo. One hour after ingestion they performed an incremental exercise test to exhaustion. The primary finding was that arginine supplementation reduced the amount of oxygen required to perform exercise. This means that individuals accomplished the same exercise load but with less energy. In other words they were more efficient after supplementing with arginine. Arginine supplementation also increased time to exhaustion by 26% during high intensity cycling.  These findings provide evidence that arginine supplementation (6 grams in a single bolus) improves exercise efficiency and tolerance.

  . Bailey SJ, Winyard PG, Vanhatalo A, Blackwell JR, Dimenna FJ, Wilkerson DP, Jones AM. Acute L-arginine supplementation reduces the O2 cost of moderate-intensity exercise and enhances high-intensity exercise tolerance. J Appl Physiol. 2010 Aug 19.