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1 Department of Physical Medicine, Rehabilitation and Sports Medicine, Center for Sports Health and Exercise Sciences at the Albergue Olímpico, University of Puerto Rico School of Medicine, Salinas, Puerto Rico 00751; 2 Department of Physical Medicine and Rehabilitation, Harvard Medical School and Spaulding Rehabilitation Hospital, Boston, Massachusetts 02114-1198; and 3 Children's Exercise and Nutrition Centre, McMaster University, Hamilton, Ontario, Canada L8N 3Z5
This study examined
the effects of beverage composition on the voluntary drinking pattern,
body fluid balance, and thermoregulation of heat-acclimatized trained
boys exercising intermittently in outdoor conditions (wet bulb globe
temperature 30.4 ± 1.0°C). Twelve boys (age 13.4 ± 0.4 yr) performed two 3-h sessions, each consisting of four
20-min cycling bouts at 60% maximal aerobic power alternating with
25-min rest. One of two beverages was assigned: unflavored water (W) or
flavored water plus 6% carbohydrate 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 W (1,470 ± 143 g). Euhydration was
maintained with CNa (+0.18% body wt), but a mild dehydration resulted
with W (
0.94% body wt; P < 0.05). Sweat loss, much higher than previously published for children of similar age, was similar between conditions (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°C), heart
rate, and all perceptual variables did not differ between conditions.
In conclusion, a flavored carbohydrate-electrolyte drink prevents
voluntary dehydration in trained heat-acclimatized boys exercising in a
tropical climate despite their large sweat losses. Because hydration
changes were minor, the thermoregulatory strain observed was similar
between conditions.
children; sweating; voluntary dehydration; body temperature; tropical climate
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