Purpose7 days L-citrulline supplementation has been reported to improve blood pressure, V. mathop { text{V}} limits {.} O2 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.Methods13 endurance runners (2 female, 31 8 y, V. mathop { text{V}} limits {.} O2peak 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 V. mathop { text{V}} limits {.} O2peak (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.ResultsTT 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.Conclusions7 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
