Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study

J Int Soc Sports Nutr. 2016 Feb 19:13:6. doi: 10.1186/s12970-016-0117-z. eCollection 2016.


Background: Many human studies report that nitric oxide (NO) improves sport performance. This is because NO is a potential modulator of blood flow, muscle energy metabolism, and mitochondrial respiration during exercise. L-Citrulline is an amino acid present in the body and is a potent endogenous precursor of L-arginine, which is a substrate for NO synthase. Here, we investigated the effect of oral L-citrulline supplementation on cycling time trial performance in humans.

Methods: A double-blind randomized placebo-controlled 2-way crossover study was employed. Twenty-two trained males consumed 2.4 g/day of L-citrulline or placebo orally for 7 days. On Day 8 they took 2.4 g of L-citrulline or placebo 1 h before a 4-km cycling time trial. Time taken to complete the 4 km cycle, along with power output/VO2 ratio (PO/VO2), plasma nitrite and nitrate (NOx) and amino acid levels, and visual analog scale (VAS) scores, was evaluated.

Results: L-Citrulline supplementation significantly increased plasma L-arginine levels and reduced completion time by 1.5 % (p < 0.05) compared with placebo. Moreover, L-citrulline significantly improved subjective feelings of muscle fatigue and concentration immediately after exercise.

Conclusions: Oral L-citrulline supplementation reduced the time take to complete a cycle ergometer exercise trial.

Trial registration: Current Controlled Trials UMIN000014278.

Keywords: Ergogenic; Human; L-Citrulline; Nitric oxide (NO); Sport performance.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adult
  • Asian People*
  • Bicycling*
  • Biomarkers / blood
  • Blood Pressure / drug effects
  • Citrulline / administration & dosage*
  • Citrulline / blood
  • Citrulline / pharmacology
  • Cross-Over Studies
  • Dietary Supplements*
  • Double-Blind Method
  • Exercise Tolerance / drug effects*
  • Humans
  • Male
  • Muscle, Skeletal / metabolism
  • Nitric Oxide Synthase / drug effects*
  • Oxygen Consumption / drug effects
  • Performance-Enhancing Substances / administration & dosage*
  • Performance-Enhancing Substances / blood
  • Performance-Enhancing Substances / pharmacology
  • Sports Nutritional Physiological Phenomena
  • Treatment Outcome


  • Biomarkers
  • Performance-Enhancing Substances
  • Citrulline
  • Nitric Oxide Synthase