Principal investigator Brian Timmons, research director of the Child Health and Exercise Medicine Program at McMaster University, says milk replaces sodium lost in sweat and helps the body retain fluid better. In addition, milk provides protein -- not found in other drinks -- that children need for muscle development and growth, Timmons says.
"Children become dehydrated during exercise, and it's important they get enough fluids, particularly before going into a second round of a game," Timmons says in a statement. "Milk is better than either a sports drink or water because it is a source of high quality protein, carbohydrates, calcium and electrolytes."
In the study, children ages 6-10 exercised in a climate chamber and then received a drink before being measured for hydration.
Timmons, an assistant professor of pediatrics of the Michael G. DeGroote School of Medicine, says active children and adults usually don't drink enough to stay hydrated during exercise, so they often have a "hydration disadvantage" when they start their next period of exercise.
However, 1 percent dehydration can result in as much as a 15 percent decrease in performance -- with an increased heart rate, core temperature and less ability to keep going -- while more significant dehydration comes with an increased risk of heat-related illness such as heat stroke, Timmons says.