Critical environmental limits for exercising heat-acclimated lean and obese boys
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Environmental limits for uncompensable heat stress, above which an imbalance between heat gain and heat loss forces body core temperature upward (i.e., the upper limits of the prescriptive zone), are unknown for children. To determine these limits, 7 lean and 7 obese 9- to 12-year-old heat-acclimated boys performed four randomized trials each on separate days to determine the critical water vapor pressure (P crit) forcing an upward inflection of body core temperature at several ambient temperatures. Subjects walked continuously on a treadmill at 30% maximal aerobic capacity at a constant dry bulb temperature (T db = 34, 36, 38 or 42°C). After a 30-min equilibration period at 9 torr, ambient water vapor pressure increased approximately 1 torr every 5-min until a distinct breakpoint in the core temperature versus time curve was evident. Compared to the lean subjects, obese subjects had significantly lower environmental limits (P < 0.03) in warm environments (P crit, for lean vs. obese, respectively = 32.9 ± 0.7 vs. 30.3 ± 0.8 torr at T db = 34°C; 29.6 ± 0.6 vs. 27.2 ± 0.9 torr at T db = 36°C; 27.8 ± 0.6 vs. 24.7 ± 0.9 torr at T db = 38°C; 25.5 ± 0.7 vs. 24.5 ± 1.5 torr at T db = 42°C). These results suggest that separate critical environmental guidelines should be tailored to lean and obese children exercising in the heat.
KeywordsChildren Thermoregulation Prescriptive zone Psychrometric chart Heat balance
We are grateful to the children for their participation in this study and to the parents for supporting them. The technical assistance of Randy McCullough, Doug Johnson, and Jane Pierzga and data collection assistance of Allison Palaio, Matt Kenney, John Jennings, Samantha Wollman, Dave Nhan and Kristin Wielkiewicz is greatly appreciated. We thank the General Clinical Research Center nursing staff for their medical support. This study was supported by National Institute of Health Grants R01-AG-07004-14 (W. L. Kenney), M01-RR-10732 (General Clinical Research Center), the Graduate Student Research Endowment from the College of Health and Human Development, The Pennsylvania State University (K. A. Dougherty), and by the Carl V. Gisolfi Memorial Research Fund from the American College of Sports Medicine Foundation (K. A. Dougherty).
Conflict of interest statement
None of the authors have relevant conflicts of interest to declare.
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