title: Critical environmental limits for exercising heat-acclimated lean and obese boys.
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.
authors.affiliation: Division of Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Children's Hospital of Philadelphia, 3535 Market Street, Room 1556, Philadelphia, PA 19104, USA. kellydoc35@aol.com
authors.forename: Kelly Anne
authors.initials: KA
authors.lastname: Dougherty
authors.forename: Mosuk
authors.initials: M
authors.lastname: Chow
authors.forename: W Larry
authors.initials: WL
authors.lastname: Kenney
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology; D002648:Child; D004777:Environment; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D008297:Male; D009765:Obesity / Q000503:physiopathology*; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D013546:Sweating / Q000502:physiology; D013851:Thinness / Q000503:physiopathology*