Dehydration Has No Influence on Simulated Motor-race Performance Despite Greater Cardiovascular and Thermoregulatory Demand

Abstract

Purpose: Motor-racing drivers compete in hot compensable environments imposing high physiological strain. Dehydration may impact a driver’s health, safety and race performance. This study examined the effect of heat-induced dehydration on performance and physiological outcomes during a simulated motor-race. Methods: Fifteen healthy men [age: 25.2±5.4 y, body mass: 84.8±10.7 kg, VIO2peak: 43.7±7.8 mL.kg-1.min-1 (mean±SD)] participated in this controlled crossover study. Participants were randomised (counter-balanced) to a no fluid trial [1.9±0.1% body mass loss (BML) via sauna exposure (wet bulb globe temperature (WBGT): 43.6±2.8°C)] and fluid trial [1.0±0.5% body mass gain via room temperature water consumption every 10 min during sauna exposure]. All participants completed ˜60 min of Australian simulated motor-racing in a heated (WBGT: 33.7±0.7°C) laboratory with no fluid provided to both trials which resulted in a 1.3±0.4 and 0.9±0.2% BML for the fluid and no fluid trials respectively. Lap time, physiological strain, heart rate and core/skin temperature were measured throughout the task. Urine [specific gravity (USG) and osmolality (Uosm)], body mass, and serum [sodium (Na), osmolality (Sosm), and plasma volume (PV)] samples were collected pre- and post- sauna and race. Results: Mean lap time was not different between trials (fluid=134.981±2.402 s, no fluid=134.718±2.147 s; p=0.293). The no fluid trial resulted in significantly higher (p<0.05) peak heart rate (129±16 vs. 121±16 beats.min-1), core temperature (38.0±0.2 vs. 37.7±0.3°C), physiological strain (4.1±1.1 vs. 3.5±1.1), Sosm (310±4 vs. 300±4 mOsm.kg-1), Na (138.7±2.1 vs. 135.8±4.5 mmol.L-1), USG [median(interquartile range): 1.025(1.024-1.027) vs. 1.006(1.004-1.013)], Uosm [942(879-1010) vs. 221(186-497) mOsm.kg-1], total body mass loss (2.7±0.3 vs. 0.9±0.4%) and change in PV (-7.9±4.2 vs. -3.3±4.2 %) than the fluid trial. Conclusion: Dehydration of ˜2.7% BML without fluid replacement had no influence on simulated race performance measured by mean lap time, despite significantly greater cardiovascular and thermoregulatory demand. Further research is warranted to assess the impact of greater cardiovascular and thermoregulatory demand from dehydration on the safety, health and well-being of drivers.