Twelve 10- to 12-year-old healthy boys performed six 70-min intermittent exercise sessions (three 20-min cycling bouts at 50%VO2max with 5 min rest in between) over a 2-week period at 35 ± 1 °C, 50 ± 5% or 60 ± 5% relative humidity. Subjects drank grape-flavored solution with 6% carbohydrate (2% glucose, 4% sucrose) and 18.0 mmol ⋅ L−1 NaCl ad libitum. Body weight (BW), heart rate, rectal temperature, thirst, and stomach fullness perception were monitored periodically. There were no differences among the six sessions in voluntary drink intake (765-902 g). hydration level (+0.75 to +1.07 %BW), sweating rate (245-263 g ⋅ m−2 ⋅ hr−1), and the other physiological and perceptual variables. A positive fluid balance was achieved in 67 out of 72 sessions. Voluntary drink intake of grape-flavored carbohydraie-NaCl beverage was consistently sufficient to prevent dehydration in 10- to 12-year-old boys during repeated exposures of exercise in the heat. This effect is likely to be achieved through a combination of physiological and behavioral mechanisms.
The authors are with the Children’s Exercise and Nutrition Centre, Pediatrics, McMaster University, Hamilton, ON L8N 3Z5, Canada. Direct correspondence to Boguslaw Wilk, Children's Exercise & Nutrition Centre. McMaster University, Chedoke Hospital Division, Evel Building 4, Hamilton, ON L8N 3Z5, Canada.