Characterizing Individual Variability In The Core Temperature And Sweating Responses To Exercise

Abstract

To normalize the influence of heat production (Hprod) and body morphology on thermoregulatory responses to exercise, between-groups comparisons of rectal temperature changes (ΔTre), whole-body sweat loss (WBSL), and steady-state local sweat rate (LSRss) should be performed at intensities that elicit same Hprod per kilogram of total body mass (W/kg), absolute evaporative requirement for heat balance (Ereq; W), and Ereq per square meter of body surface area (BSA; W/m2), respectively. However, it is unknown how well these parameters, and others related to aerobic fitness and morphology, explain individual variability in the aforementioned thermoregulatory responses. PURPOSE: To determine the contribution of various biophysical and physiological factors to the explained variance in the ΔTre, WBSL, and LSRss responses to exercise in compensable conditions. METHODS: A cohort of 37 subjects, heterogeneous for maximum oxygen uptake (VO2max) and body morphology, completed multiple trials consisting of 60 min of exercise in temperate conditions (25°C, 33% RH, 1.2 m/s air velocity) at intensities corresponding to a range of target absolute Hprod (410-918 W) and relative intensities (32.2-82.0% of VO2max). Metabolic rate, rectal and skin temperatures, and forearm LSR were measured continuously; WBSL was estimated from changes in body mass. RESULTS: Individual characteristics and experimental data were normally distributed. Individual variation in ΔTre was correlated with Hprod in W/kg (β = 0.673, P < 0.001) and body mass (β = −0.190, P = 0.027) with an adjusted R2 of 0.535 (P < 0.001). Additionally, only Ereq in W (β = 0.858, P < 0.001) correlated with WBSL (adjusted R2 = 0.732, P < 0.001), and only Ereq in W/m2 (β = 0.634, P < 0.001) correlated with LSRss (adjusted R2 = 0.631, P < 0.001). Factors related to body composition and aerobic fitness did not correlate with the residual variance. CONCLUSION: These data show that investigators must first consider factors related to Hprod, Ereq, body mass, and BSA when examining possible physiological differences in the core temperature and thermoregulatory sweating responses to exercise. Supported by NSERC Discovery Grant #386143-2010