Background
L-citrulline is an amino acid that is an endogenous precursor of L-arginine and contributes to generating nitric oxide (NO). L-citrulline is known for increasing plasma L-arginine and NO more effectively than equivalent doses of L-arginine. NO plays an important role in sport performance but it is presently unknown whether L-citrulline enhances sport performance during rowing ergometer competition in humans. The aim of this study is to investigate the effect of oral supplementation of L-citrulline on cycling time trial performance.
Methods
A randomized double-blind crossover study design was used. Twenty two well-trained males, aged between 20 and 39, consumed 2.4 g / day of L-citrulline or placebo for 7 days and they took 2.4 g of L-citrulline or placebo 1 hour before 4 km cycling time trial on day 8. Completion time of 4 km cycling, power output / VO2 ratio (PO / VO2), plasma NOx, amino acids, Visual Analog Scale (VAS) were evaluated.
Results
L-citrulline supplementation significantly improved cycling time trial performance by 1.5% (p < 0.05) and increased PO / VO2 during performance (p < 0.1). Moreover there was a correlation between plasma NOx and PO / VO2 (r = 0.47, p < 0.01) in L-citrulline group. L-citrulline significantly increased plasma L-citrulline and L-arginine, and improved the subjective feeling of muscular fatigue and concentration (p < 0.05).
Conclusion
Oral L-citrulline supplementation enhances cycling time trial performance by improving PO / VO2 through up-regulation of plasma NO availability.