Drink composition, voluntary drinking, and fluid balance in exercising, trained, heat-acclimatized boys

This study examined the effects of beverage composition on the voluntary dr inking pattern, body fluid balance, and thermoregulation of heat-acclimatiz ed trained boys exercising intermittently in outdoor conditions (wet bulb g lobe temperature 30.4 +/- 1.0 degrees C). Twelve boys (age 13.4 +/- 0.4 yr) performed two 3-h sessions, each consisting of four 20-min cycling bouts a t 60% maximal aerobic power alternating with 25-min rest. One of two bevera ges was assigned: unflavored water (W) or flavored water plus 6% carbohydra te and 18 mmol/l Na (CNa). Drinking was ad libitum. Total intake was higher (P < 0.05) during CNa (1,943 +/- 190 g) compared with SV (1,470 +/- 143 g) . Euhydration was maintained with CNa (+0.18% body wt), but a mild dehydrat ion resulted with W (-0.94% body wt; P < 0.05). Sweat loss, much higher tha n previously published for children of similar age, was similar between con ditions (CNa = 1,644.7 +/- 117.5; W = 1,750.2 +/- 152.7 g. The increase in rectal temperature (CNa 0.86 +/- 0.3; W = 0.76 +/- 0.1 degrees C), heart ra te, and all perceptual variables did not differ between conditions. In conc lusion, a flavored carbohydrate-electrolyte drink prevents voluntary dehydr ation in trained heat-acclimatized boys exercising in a tropical climate de spite their large sweat losses. Because hydration changes were minor, the t hermoregulatory strain observed was similar between conditions.