Abstract
Maintaining hydration is understood to minimize deleterious effects of exercise-induced hyperthermia. Stimulation of arteriovenous anastomoses (AVAs) to induce cooling following hyperthermia is associated with positive changes in cooling time, thermo-physiological and cognitive function, and perception of thermal strain. However, the impact of hydration on these responses is unclear. PURPOSE: To determine the impact of hydration during passive hyperthermia and subsequent AVA-stimulated cooling on thermo-physiological function and cognitive motor skill. METHODS: Eight participants (23±6 yrs; 172±10 cm; 69.3±10.8 kg) reported either dehydrated (USG>1.020) or hydrated (USG<1.010). Waking hydration status was assessed using a hand-held pen refractometer. Hyperthermia (Tre 39.5°C) was induced whilst seated in circulated warm water (42°C) to the level of the clavicle. Post-hyperthermia cooling was performed by immersing one hand and forearm in circulated cold water (10°C) until Tre≤38.0°C. Heart rate (HR) was monitored continuously during hyperthermia and cooling. A battery of cognitive motor skill tests (Stroop Word Color [SWC] and Trail-Making Task [TMT]), quadriceps maximal voluntary contraction (MVC), and perceived thermal sensation (TS) were assessed at baseline, upon reaching hyperthermia, and when Tre≤38.0°C. Hydration status and cooling time, and thermo-physiological and cognitive motor skill comparisons were made using two-way and three-way ANOVA with repeated measures, respectively. RESULTS: Time to cool improved with AVA stimulation (24±9 min vs. 40±14 min, p=0.001), and Tre (p=0.006), HR (p=0.004) and TS (p=0.004) showed positive interaction effects (cooling and time). However, hydration had no effect or interaction effect (p>0.05) on thermo-physiological function. Trail-making task was negatively impacted by hyperthermia (Baseline 38±12 s vs. Hyperthermia 50±22 s vs. Cooled 41±15 s, p=0.017), and performance of SWC (p=0.077) trended towards a positive interaction effect (cooling and time). However, hydration had no effect or interaction effect (p>0.05) on cognitive motor skill. CONCLUSION: Hydration status may have little impact on thermo-physiological function or cognitive motor skill during passive hyperthermia or subsequent cooling.
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