EFFECTS OF HYDRATION ON PHYSIOLOGICAL INDICATORS DURING HEAT ACCLIMATION

Effects of hydration on physiological indicators during heat acclimation N. Mickelson, M.Schleh, B. Ruby FACSM, C.L. Dumke FACSM University of Montana, Missoula, MT. Hydration of wildland firefighters (WLFF) during heat acclimation trials may impact performance by reducing physiological strain. By inducing dehydration in a controlled setting, physiological adaptations such as increased sweat rate and cardiovascular strain may be enhanced. PURPOSE: To investigate the impact hydration status (dehydrated/ euhydrated) has, through mitigated fluid delivery, on levels of hydration (% dehydration), sweat rate (SR), heart rate (HR), and rating of perceived exertion (RPE). METHODS: Ten aerobically fit male subjects (age=23.0±0.9, weight=82.1±4.6kg) underwent three heat acclimation trials on alternate days in an environmental chamber (40°C, 30%RH) for 90 min at 50%VO2max. Subjects wore WLFF Nomex pants, yellow button up and 100% cotton t-shirt. Fluid delivery was controlled to induce 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 in a random crossover design. Rating of perceived exertion (RPE) and heart rate (HR) were measured every 15 minutes throughout the 90 minute 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 interaction for treatment (p-1) or RPE (DEH=15±1.00, 14.33±1.12, 14.00±1.66, EUH=14.44±1.24, 14.11±1.27, 14.00±1.50) for acclimation days 1, 2, and 3 respectively. CONCLUSIONS: Our data suggests that controlled dehydration during 3 days of short term heat acclimation results in elevated percent dehydration, but does not jeopardize HR, SR, or RPE. This project was supported by the US Forest Servic