Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-arginine is an amino acid frequently marketed as an exercise and athletic performance aid, largely because it is a precursor to nitric oxide (NO), a molecule that promotes vasodilation and increased blood flow to skeletal muscles during exercise. The theoretical basis is that enhanced NO production could improve oxygen and nutrient delivery, thereby boosting exercise capacity, endurance, and muscle recovery.

Scientific studies, however, have produced mixed results. Some small-scale trials have suggested that L-arginine supplementation may modestly increase exercise tolerance, particularly in untrained or moderately trained individuals. For example, a few studies have reported slightly improved aerobic and anaerobic performance or reduced perceived exertion. However, larger and more rigorously controlled studies in well-trained athletes generally show little to no benefit. A 2016 meta-analysis concluded that L-arginine supplementation does not significantly enhance endurance or strength performance in most populations.

Safety-wise, L-arginine appears to be well-tolerated at typical dosages, but gastrointestinal discomfort can occur. Overall, while there is a plausible physiological mechanism and some limited human data supporting its use, the current body of evidence does not strongly support L-arginine as an effective athletic or exercise aid, particularly for highly trained individuals. Thus, the scientific evidence is rated low (2 out of 5) for this use.

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