The average male body is 60% water and the average female body is 50% water. Sufficient hydration is critical to performing your best.
Dehydration causes heart rate and body temperature to rise more when exercising.
Dehydration hurts performance by reducing your ability to work.
Dehydration increases the risk of injury because of physical and mental fatigue.
Dehydration, when severe, causes heat illness in the form of heat exhaustion (less severe) and heat stroke (very severe).
These environmental conditions make it more difficult for the body to dissipate heat when exercising.
Know the signs.
THIRST ALONE IS NOT AN ADEQUATE INDICATOR OF DEHYDRATION.
By the time you notice you're thirsty, you could already be dehydrated.
Check your urine.
Collect a urine sample in a clear plastic container. Hold it up to bright light for comparison to the chart on this page.
Watch your weight.
Weigh yourself before and after strenuous exercise to track how much water you're losing and to see if you've replaced it by the next workout.
How Much and When to Drink
Can you drink too much?
Yes, too much water dilutes the body's sodium levels, creating an electrolyte imbalance.
What to Drink
Sport drinks are the preferred choice when you're exercising over an hour. They not only replace water, but they replace electrolytes and carbohydrates needed to fuel the muscles.
Water is an excellent choice if the exercise is not likely to deplete carbohydrates and electrolytes.
Fruit juices, which are rich in nutrients, are good refreshment beverages. They're better as post-exercise drinks because they're absorbed a little more slowly into the body than are sports drinks.
Soft drinks contain water and sugar, which helps fuel the muscles but provides no other nutrients. They're acceptable but not optimal for rehydration.
Diet soft drinks contain water without any nutrients. They, too, are acceptable, but not optimal.
Beer and other alcoholic drinks in general impair rehydration, are a poor source of nutrients, and do not help you recover for the next exercise event.