Estimating Core Temperature Rise During Exercise with Over-Dressing from VO2 and Skin Temperatures

Abstract

Heat acclimation has been shown to improve aerobic exercise performance in both hot and temperate environments. Many athletes and teams seeking the benefits of heat acclimation have incorporated environmental heat or over-dressing during exercise into their training programs. However, most athletes are not monitoring core temperature, and may risk under- or over-stressing their thermoregulatory system, compromising ideal heat acclimation adaptations. PURPOSE: To examine the ability of non-invasive measurements to predict core temperature (Tre) rise during treadmill running in hot conditions (classic heat acclimation) and temperate conditions while wearing multiple insulative and vapour-impermeable layers of clothing (heat acclimation through over-dressing). METHODS: Nine trained runners (6M, 3F; Age: 23 ± 7 years; VO2max: 60.5 ± 9.8 ml/kg/min; Body Mass: 62.3 ± 8.4 kg; body surface area [BSA]:1.75 ± 0.18 m2) participated in this study. Subjects ran for 60 min at 50% VO2max on a treadmill in hot (40°C, 30%rh) and temperate (15°C, 50%rh) environments, with additional clothing in the temperate environment. Clothing was configured based on biophysical modelling equations in an attempt to match thermal strain imposed by the hot environment. Heart rate, Tre, VO2, and skin temperature (Tsk) were measured throughout exercise. Key anthropometric and physiological variables were examined using multiple linear regression analysis to predict change in rectal temperature ([INCREMENT]Tre;°C/hr). RESULTS: To estimate [INCREMENT]Tre during exercise in hot and temperate environments, the equation [INCREMENT]Tre (°C/hr) = −2.881 + (1.229*VO2) + (0.105*Tsk/BSA) was calculated using regression analysis (p=0.001; r=0.80) for exercise VO2 (L/min) and Tsk/BSA (°C/m2), using a range of VO2 (1.31-2.74L/min), Tsk (33.0-37.0°C), and BSA (1.40-1.98m2). CONCLUSIONS: The [INCREMENT]Tre prediction equation can be used to accurately predict core temperature rise under the environmental conditions tested. This information can be used to develop exercise-heat acclimation protocols in settings where the invasiveness, cost, or other barriers to directly measuring core temperature are a concern.