Synopsis

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

L-citrulline is an amino acid that has been investigated for its role in enhancing endurance performance, primarily through its effects on nitric oxide (NO) production and vasodilation. When ingested, L-citrulline is converted by the kidneys into L-arginine, which serves as a precursor for NO synthesis. Increased NO can promote blood vessel dilation, thereby improving blood flow and oxygen delivery to muscles during exercise.

Several clinical studies have evaluated the impact of L-citrulline supplementation on exercise performance, particularly endurance. For example, a 2010 double-blind, placebo-controlled study found that citrulline malate supplementation improved cycling performance and reduced the sensation of muscle fatigue in healthy adults. Other studies have shown increased aerobic energy production and delayed onset of muscle fatigue during submaximal exercise. However, the magnitude of benefit tends to be moderate, and not all research has found statistically significant improvements in endurance outcomes.

Meta-analyses and systematic reviews indicate that while L-citrulline supplementation appears to have a small but positive effect on exercise performance and endurance in both trained and untrained individuals, the effects are not universally observed and may depend on dosage, duration, and the specific form used (e.g., L-citrulline vs. citrulline malate). The evidence is stronger for its acute ergogenic effects rather than long-term adaptations. Overall, while the scientific foundation is present, the strength of evidence is moderate, justifying a rating of 3 out of 5.

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