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Randomized Controlled Trial
. 2010 Mar;108(4):779-89.
doi: 10.1007/s00421-009-1290-4.

Critical environmental limits for exercising heat-acclimated lean and obese boys

Kelly Anne Dougherty  1 , Mosuk Chow, W Larry Kenney
Affiliations
Randomized Controlled Trial

Critical environmental limits for exercising heat-acclimated lean and obese boys

Kelly Anne Dougherty et al. Eur J Appl Physiol. 2010 Mar.

Abstract

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 degrees 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 degrees C; 29.6 +/- 0.6 vs. 27.2 +/- 0.9 torr at T (db) = 36 degrees C; 27.8 +/- 0.6 vs. 24.7 +/- 0.9 torr at T (db) = 38 degrees C; 25.5 +/- 0.7 vs. 24.5 +/- 1.5 torr at T (db) = 42 degrees C). These results suggest that separate critical environmental guidelines should be tailored to lean and obese children exercising in the heat.

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Conflict of interest statement

Conflict of interest statement None of the authors have relevant conflicts of interest to declare.

Figures

Fig. 1
Fig. 1
A representative critical water vapor pressure (Pcrit) test illustrating the typical time course of body core temperature (Tc), heart rate (HR), and mean skin temperature (Tsk) responses to exercise and rising ambient water vapor pressure (Pa)
Fig. 2
Fig. 2
Critical environmental limits on a standard psychrometric chart. Values are means ± SE for 7 lean and 7 obese subjects at 34, 36 and 38°C and 7 lean and 5 obese subjects at 42°C. Compared to lean subjects, obese subjects consistently had significantly lower critical water vapor pressure (Pcrit) values in each warm environment. *Significant group difference at P < 0.03
See this image and copyright information in PMC

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