Mateos-Roman, A., & Aragon-Vargas, L. F. (2012). Voluntary fluid intake with milk or chocolate milk in boys exercising in the heat. Presentation 2291 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

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This study compared fluid balance and voluntary intake in 10-to-14- year-old boys (N = 31), when they combined milk or chocolate milk with water during exercise in the heat. In addition, palatability and gastrointestinal symptoms were assessed. Ss from a junior soccer team, exercised in a controlled environment chamber (~31.6C and ~47.3 relative humidity), at ~67.4% maximum heart rate, using a cycle ergometer and a treadmill. Ss alternated 20 minutes of exercise with 10 minutes of rest on four consecutive occasions, for a total of approximately two hours in the chamber. Ad libitum fluid intake was monitored from the simultaneous presentation of water and partially skimmed milk (session A) or water and partially skimmed chocolate milk (session B). The drinks had a temperature of ~15.9C. Fluid balance was calculated from differences in nude body weight. Palatability and gastrointestinal symptoms were reported upon arrival, and before, during, and at the end of the exercise session.

Initial conditions were the same for sessions A and B. Sweat rates and fluid balance were the same for both sessions. A significant difference was found for time: a positive fluid balance was observed during the first hour of exercise, but not during the second hour. Voluntary intake was the same for both sessions, but different over time. Boys drank more fluid during the first hour of sessions A and B than during the second hour. Chocolate milk showed the highest palatability scores and water showed the lowest. Gastrointestinal symptoms were very low (for abdominal pain, fullness, and side stitch).

Implication. When presented simultaneously with water, both partially-skimmed milk and partially-skimmed chocolate milk were effective in preventing voluntary dehydration in boys exercising in the heat. Palatability scores for the two fluids were favorable and gastrointestinal symptoms not clinically relevant.

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