Synopsis

Source of validity: Scientific
Rating (out of 5): 3

Nitric oxide (NO) is a molecule naturally produced by the body that plays several roles in vascular and muscular function. In the context of exercise, nitric oxide is widely promoted for its vasodilatory effects, which can increase blood flow to active muscles. This enhanced blood flow is theorized to improve the delivery of oxygen and nutrients during exercise, potentially enhancing performance, endurance, and recovery. Many supplements marketed for exercise support (commonly called "NO boosters") contain precursors such as L-arginine or L-citrulline, which the body can convert into nitric oxide.

The scientific evidence for nitric oxide’s benefits in exercise is mixed but generally supportive, especially in specific populations and scenarios. Systematic reviews and meta-analyses indicate that NO-boosting supplements, particularly those containing L-citrulline and dietary nitrates (e.g., beetroot juice), can modestly improve exercise performance, particularly in aerobic and high-intensity endurance activities. Effects are more pronounced in less trained individuals and during submaximal exercise. The evidence is less consistent for highly trained athletes or during maximal strength/power activities.

The mechanisms of action are reasonably well understood, and there is scientific consensus regarding NO’s role in vasodilation. However, the magnitude of benefit and the specific populations who benefit most are still being investigated. Overall, nitric oxide use for exercise support is justified by scientific evidence, but the effect size is moderate and not universal.

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