title: Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study.
abstract: 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.
  
  
  BACKGROUND
  Current Controlled Trials UMIN000014278.
authors.affiliation: Healthcare Products Development Center, KYOWA HAKKO BIO CO., LTD., 2, Miyukigaoka, Tsukuba, Ibaraki 305-0841 Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Suzuki
authors.affiliation: Healthcare Products Development Center, KYOWA HAKKO BIO CO., LTD., 2, Miyukigaoka, Tsukuba, Ibaraki 305-0841 Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Morita
authors.affiliation: Laboratory of Pharmacognosy, School of Pharmaceutical Sciences, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo, 108-0861 Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Healthcare Products Development Center, KYOWA HAKKO BIO CO., LTD., 2, Miyukigaoka, Tsukuba, Ibaraki 305-0841 Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Kamimura
mesh_terms: D000284:Administration, Oral; D000328:Adult; D044466:Asian People; D001642:Bicycling; D015415:Biomarkers / Q000097:blood; D001794:Blood Pressure / Q000187:drug effects; D002956:Citrulline / Q000008:administration & dosage* / Q000097:blood / Q000494:pharmacology; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D017079:Exercise Tolerance / Q000187:drug effects*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000187:drug effects*; D010101:Oxygen Consumption / Q000187:drug effects; D058573:Performance-Enhancing Substances / Q000008:administration & dosage* / Q000097:blood / Q000494:pharmacology; D064133:Sports Nutritional Physiological Phenomena; D016896:Treatment Outcome
chemical_list: D015415:Biomarkers; D058573:Performance-Enhancing Substances; D002956:Citrulline; D019001:Nitric Oxide Synthase
keywords: Ergogenic; Human; L-Citrulline; Nitric oxide (NO); Sport performance