7 days of L-citrulline supplementation does not improve running performance in the heat whilst in a hypohydrated state

Abstract

Purpose 7 days L-citrulline supplementation has been reported to improve blood pressure, $$\mathop {\text{V}}\limits^{.}$$ V . O 2 kinetics, gastrointestinal (GI) perfusion and endurance cycling performance through increasing arterial blood flow. In situations where blood volume is compromised (e.g., hyperthermia/hypohydration), L-citrulline may improve thermoregulation and exercise performance by redistributing blood flow to aid heat loss and/or muscle function. This study assessed 7 days L-citrulline supplementation on running performance in the heat, whilst mildly hypohydrated. Methods 13 endurance runners (2 female, 31 ± 8 y, $$\mathop {\text{V}}\limits^{.}$$ V . O 2 peak 60 ± 6 mL/kg/min) participated in a randomised crossover study with 7 days L-citrulline (CIT; 6 g/d) or placebo (maltodextrin powder; PLA) supplementation. Participants completed a 50 min running ‘preload’ at 65% $$\mathop {\text{V}}\limits^{.}$$ V . O 2 peak (32 °C, 50% relative humidity) to induce hyperthermia and hypohydration before a 3 km running time trial (TT). Body mass and blood samples were collected at baseline, pre-preload, post-preload and post-TT, whilst core and skin temperature, heart rate and perceptual responses were collected periodically throughout. Results TT performance was not different between trials (CIT 865 ± 142 s; PLA 892 ± 154 s; P = 0.437). Core and skin temperature and heart rate ( P ≥ 0.270), hydration (sweat rate, plasma volume, osmolality) indices ( P ≥ 0.216), GI damage ( P ≥ 0.260) and perceptual responses ( P ≥ 0.610) were not different between trials during the preload and TT. Conclusions 7 days of L-citrulline supplementation had no effect on 3 km running performance in the heat or any effects on thermoregulation or GI damage in trained runners in a hypohydrated state.

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