It may be hard to believe, but while you are standing on the sidelines bundled in a sweater on a crisp fall day watching your child running up and down the soccer field, she may become dehydrated. Dehydration can begin when an athlete loses as little as 1 percent of body weight. In a 70-pound child, that is less than 1 pound of weight lost through sweat. As little as a 2% decrease in body weight from fluid loss (e.g. 1.2 lb for a 60-lb athlete) can lead to a significant decrease in muscular strength and stamina. If your child tires easily and repeatedly in practice and appears irritable, and her performance suddenly declines, dehydration, and/or inadequate calorie intake may be the cause.