ABSTRACT
The purposes of this study were to examine the thermoregulatory and body fluid balance responses in chronically heat acclimatized children, i.e., indigenous to a tropical climate, during exercise in four outdoor conditions and the effects of dehydration on their thermoregulatory response. Nine children (age = 13.3 ± 1.9 yr, VO2 max = 45.5 ± 9.2 ml · kg-1 · min-1 ) cycled at 60% VO2 max each under four conditions: sun exposure voluntary drinking (SuVD), sun exposure forced drinking (SuFD), shaded voluntary drinking (ShVD), and shaded forced drinking (ShFD). Exercise sessions consisted of four 20-min exercise bouts alternating with 25-min rest periods. Globe temperature and the WBGT index were higher during SuVD and SuFD compared to ShVD and ShFD (P < 0.05). The change in rectal temperature, metabolic heat production, and heat storage did not differ among the conditions. Total water intake (% IBW) was higher during SuFD (4.1 ± 0.01) and ShFD (3.7 ± 0.1) compared to SuVD (2.1 ± 0.1) and ShVD (1.0 ± 0.1) and during SuVD compared to ShVD (P < 0.05). Sweating rate (L · hr-1 ) was higher during SuFD (0.7 ± 0.1) and ShFD (0.6 ± 0.1) compared to SuVD (0.5 ± 0.1) and ShVD (0.4 ± 0.1) (P < 0.05). Total fluid loss did not differ among conditions (SuVD = 1.7 ± 0.4; SuFD = 1.5 ± 0.4; ShVD = 2.1 ± 0.2; ShFD = 1.3 ± 0.3). Results indicate that when exercising in a tropical climate, chronically heat acclimatized children demonstrate mild voluntary dehydration and adequate heat dissipation. © 1995 Wiley-Liss, Inc.
