Nitric oxide, a gas manufactured by the body from amino acids, is a natural vasodilator, or blood vessel relaxer. The dilation results in increased blood flow that carries more oxygen and nutrients to muscle tissue. Makers of supplements containing L-arginine, or simply arginine, claim the products increase nitric oxide levels in the blood which they say aids in building lean muscle mass.
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Serious bodybuilders rate workouts based on the concept of “muscle pump,” the blood-engorged feeling of tightness in the targeted muscle group that is indicative of rigorous training. Users of arginine supplements contend that the slight uptick in nitric oxide resulting from aginine conversion prolongs “muscle pump,” leading to increased stamina and endurance.
L-arginine has demonstrated positive results in clinical trials for conditions such as erectile dysfunction and weight loss associated with illness, particularly in the retention of lean muscle mass, according to Medline Plus, a division of the National Institutes of Health. Bodybuilders point to these results as evidence that a short-term boost in nitric oxide levels in the blood associated with arginine conversion can lead to greater muscle development and the creation of new muscle tissue. Direct studies are mixed, however, including a 2010 survey conducted by R. J. Bloomer, et al, published in the “Journal of Strength and Conditioning Research.” In it, researchers found a minimal increase in nitric oxide levels in the blood and virtually no change in blood pressure or heart rate for the supplement group compared with the control group.
Most of the body’s arginine needs are met by a standard diet, though some people suffer from protein malnutrition or other conditions that necessitate supplementation. Bodybuilders who “megadose” with arginine, particularly if they eat a diet rich in red meat, poultry, fish and dairy are subject to common amino acid overdose side effects like diarrhea, nausea and fatigue. People who already have low blood pressure should not take arginine supplements as the resulting nitric oxide concentrations dilate the blood vessels and could cause the blood pressure to drop even further, according to Medline Plus.
As of 2010, supplements containing arginine are not banned by any of the major U.S. sports organizations, according to the the National Center for Drug Free Sport. However, supplements containing arginine may contain additional ingredients that are banned by some governing bodies. Caffeine makes NCAA’s list of banned substances, and it is a primary ingredient in most aginine supplement brands. Synephrine, another stimulant used in arginine supplements, is also banned by the NCAA and many other organizations, says Rachel Olander of Drug Free Sport.