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

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. © 2016 suzuki et al.