Hiking Time Trial Performance in the Heat with Real-Time Observation of Heat Strain, Hydration Status and Fluid Intake Behavior

International Journal of Environmental Research and Public Health
Joshua D LinsellFloris C Wardenaar

Abstract

This study investigated the real-time progression of heat strain in mountain hikers during time trials (TT). Participants (n = 12; 7M/5F; age 21.6 ± 2.47) attempted to climb Tempe Butte (~1.1 mi) four times in HOT and MOD trials (wet bulb globe temperature 31.6 °C vs. 19.0 °C). Performance, physiological outcomes, and fluid intake behavior were measured in real-time. Hot conditions significantly impaired hiking TT performance by 11%, reduced aerobic capacity by 7%, increased peak rate of perceived exertion (RPE) by 19%, and elevated core temperature (Tc) by 0.7 °C compared to MOD (all p < 0.03). Less-aerobically-fit participants were most negatively-affected by heat stress. Based on sweat lost, participants in HOT required 2.26 ± 0.91 L of fluids, brought 1.52 ± 0.83 L, and consumed 1.54 ± 0.49 L, losing an average of 1.1% ± 1.0%BM. Participants in MOD required 1.28 ± 0.39 L of fluids, brought 1.57 ± 1.09 L, and consumed 0.79 ± 0.57 L, losing an average of 1.0% ± 0.8%BM. Morning-after urine specific gravity (USG) values revealed 75% of hikers were hypohydrated (USG ≥ 1.020) after HOT; 67% after MOD. Heat stress impairs hiking TT performance while increasing RPE and Tc. Fitter participants showed less performance and physiologic...Continue Reading

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