During exercise, try to drink approximately one cup of fluid every 20 minutes. A good indicator of adequate hydration is urine color and volume. Within 60 minutes of exercise, passing light-colored urine of normal to above average volume is a good indicator of adequate hydration. Another method of monitoring hydration levels is to weigh yourself before and after exercise. There is some controversy as to the best beverage for fluid replacement.
Water is generally the fluid of choice because it moves rapidly through the stomach.
Drinks containing caffeine and alcohol should be avoided as they are diuretics and thus increase urine production. Heat illness occurs at differing levels of severity. The least severe is heat cramps, and the most severe is heat stroke. If not properly treated, heat cramps can progress to heat exhaustion or even to heat stroke, which is a medical emergency. Heat cramps typically occur in the calf muscle.