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THE EFFECT OF HYDRATION STATUS ON PHYSIOLOGICAL MARKERS DURING HEAT ACCLIMATION

Abstract

C. Alfiero, K. Nickol, M.Schleh, B. Ruby FACSM, C.L. Dumke FACSM

University of Montana, Missoula, MT

The hydration status of wildland firefighters (WLFF) during heat acclimation trials may impact long-term work performance by attenuating physiological strain. By inducing dehydration by a mitigated fluid delivery method in a controlled setting, physiological adaptations such as increased sweat rate and cardiovascular strain may be ameliorated. PURPOSE: To investigate the impact of fluid delivery that affects hydration status (dehydrated/ euhydrated) on levels of hydration (% dehydration), sweat rate (SR), heart rate (HR), and rating of perceived exertion (RPE). METHODS: In a randomized cross-over protocol, five aerobically fit male subjects (age=23.0±0.9, weight=82.1±4.6kg, 53.2±1.6) underwent three heat acclimation trials on alternate days in an environmental chamber (40°C, 30%RH) for 90 min at 50%VO2max. Fluid delivery was administered to promote either dehydration (DEH=0.5 ml*kg-1*15 min-1) or euhydration (EUH=2.0 ml*kg-1*15 min-1). After a five week washout period three subsequent trials were held in the alternate hydrated state. Participants wore standard WLFF Nomex green pants, yellow shirt with 100% cotton base layer. Rating of perceived exertion (RPE) and heart rate (HR) were measured every 30 min throughout the 90 min trial. Pre and post bodyweight were measured to determine sweat rate and percent dehydration. Statistics were performed as a 2 (trt) x 3 (day) analysis of variance (ANOVA) with repeated measures. RESULTS: There was a significant trt*day interaction (p=0.009) in average RPE (DEH=13.4±0.2, 12.7±0.2, 12.7±0.4, EUH=12.33±.252, 12.17±.252, 11.9±0.4) between DEH and EUH over the three days. There was a significant effect of treatment (p-1) for acclimation bouts 1, 2, and 3 respectively. CONCLUSIONS: Our data suggests that controlled dehydration during 3 days of heat acclimation results in elevated RPE and percent dehydration, but does not jeopardize HR or SR.

This project was supported by the US Forest Service.

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