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

Joshua D. Linsell, Emily C. Pelham, David M. Hondula and Floris C. Wardenaar
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Joshua D. Linsell: College of Health Solutions, Arizona State University, Phoenix, AZ 85004, USA
Emily C. Pelham: College of Health Solutions, Arizona State University, Phoenix, AZ 85004, USA
David M. Hondula: School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, AZ 85281, USA
Floris C. Wardenaar: College of Health Solutions, Arizona State University, Phoenix, AZ 85004, USA

IJERPH, 2020, vol. 17, issue 11, 1-11

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 (T c ) 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 T c . Fitter participants showed less performance and physiological impairment from heat stress. Although hikers in both conditions lost similar body weight, hikers were limited in HOT by fluid availability, whereas in MOD, fluid was available and dehydration was voluntary.

Keywords: exertional heat illness (EHI); heat strain; heat stress; mountain search and rescue; biometeorology; dehydration; dietary behavior; public health and safety (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2020
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