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Journal of the International Society of Sports Nutrition

Open Access

Oral L-citrulline supplementation enhances cycling time trial performance in healthy well-trained males

  • Takashi Suzuki1,
  • Masahiko Morita1,
  • Yoshinori Kobayashi2 and
  • Ayako Kamimura1
Journal of the International Society of Sports Nutrition201512(Suppl 1):P52

Published: 21 September 2015


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.


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.


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).


Oral L-citrulline supplementation enhances cycling time trial performance by improving PO / VO2 through up-regulation of plasma NO availability.

Authors’ Affiliations

Healthcare Products, Development Center, KYOWA HAKKO BIO Co., Ltd, Tokyo, Japan
Laboratory of Pharmacognosy, School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan


© Suzuki et al. 2015

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.