Title

The Effect of Dehydration on Heat Acclimation

Presentation Type

Poster

Abstract

Minimizing heat-related illness for occupations in hot environments is essential. We hypothesize that short-term heat acclimation (STHA) in a state of hypohydration will improve cardiovascular and perceptual strain associated with heat stress, accelerating heat acclimatization. PURPOSE: To determine the impact of hydration status during STHA on heat adaptations. METHODS: Ten aerobically fit male subjects (23±1.00yrs, 82.1±2.14kg, 53.18±1.63mL•kg-1•min-1 VO2 max, 13.8%±1.31%BF) completed a heat stress test (HST) two days prior to, and following three acclimation bouts over six days. HST/acclimation bouts consisted of 90-minute treadmill walking at 50% VO2 max in hot conditions (40, 30%RH). Additionally, a performance test was conducted that the end of each HST. In a randomized crossover design, fluids were administered during STHA bouts to promote a dehydrated (DEH=0.5 mL/kg) or a euhydrated (EUH=2.0 mL/kg) state. A five-week washout period separated DEH from EUH trials. Participants wore standard wildland firefighter NoMex clothing with a cotton shirt. Peak heart rate (HR), peak rate of perceived exertion (RPE), percent dehydration (%DEH), sweat rate (SR), and peak core temperature (PCT) were analyzed by a 2(trt) X 2(trial)ANOVA. RESULTS: HR and RPE both decreased significantly from PRE to POST with no significant difference between treatments. SR showed a time and trtXtime interaction that nearly reached significance (p=0.054) with greater increases in the DEH trial. Conclusion: Our data suggests STHA reduces physiological and perceptual strain, regardless of hydration status. However controlled dehydration improved SR, suggesting the protocol may lead to greater heat adaptations during STHA.

Category

Life Sciences

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Apr 15th, 3:00 PM Apr 15th, 4:00 PM

The Effect of Dehydration on Heat Acclimation

Minimizing heat-related illness for occupations in hot environments is essential. We hypothesize that short-term heat acclimation (STHA) in a state of hypohydration will improve cardiovascular and perceptual strain associated with heat stress, accelerating heat acclimatization. PURPOSE: To determine the impact of hydration status during STHA on heat adaptations. METHODS: Ten aerobically fit male subjects (23±1.00yrs, 82.1±2.14kg, 53.18±1.63mL•kg-1•min-1 VO2 max, 13.8%±1.31%BF) completed a heat stress test (HST) two days prior to, and following three acclimation bouts over six days. HST/acclimation bouts consisted of 90-minute treadmill walking at 50% VO2 max in hot conditions (40, 30%RH). Additionally, a performance test was conducted that the end of each HST. In a randomized crossover design, fluids were administered during STHA bouts to promote a dehydrated (DEH=0.5 mL/kg) or a euhydrated (EUH=2.0 mL/kg) state. A five-week washout period separated DEH from EUH trials. Participants wore standard wildland firefighter NoMex clothing with a cotton shirt. Peak heart rate (HR), peak rate of perceived exertion (RPE), percent dehydration (%DEH), sweat rate (SR), and peak core temperature (PCT) were analyzed by a 2(trt) X 2(trial)ANOVA. RESULTS: HR and RPE both decreased significantly from PRE to POST with no significant difference between treatments. SR showed a time and trtXtime interaction that nearly reached significance (p=0.054) with greater increases in the DEH trial. Conclusion: Our data suggests STHA reduces physiological and perceptual strain, regardless of hydration status. However controlled dehydration improved SR, suggesting the protocol may lead to greater heat adaptations during STHA.