During heat stroke, your temperature can rise above 105 degrees Fahrenheit. At that point, you no longer sweat, and seizures, coma or death may result. Remember: Blood not only carries oxygen to your working muscles, it carries it to all of your vital organs (like your brain), too.

How do you get enough water? Drink early and often during your workout. How much? How often? Six to eight ounces every fifteen minutes. That may sound like a lot, but it is only the equivalent of one large bicycle water bottle per hour. If you can't handle that much water at once, drink smaller amounts every ten minutes.

You should follow the same guidelines when exercising indoors. You can sweat a whole lot when spending 45 minutes or more on a stepper, treadmill or stationary bike.

Don't wait until you're thirsty to start drinking water. The sensation of thirst is triggered by the hypothalamus in the brain. It measures the concentration of salts in your blood. As blood volume goes down due to sweating, the concentration of salts goes up, and the hypothalamus sends the signal to start drinking. By the time this occurs, you've already lost a significant amount of fluid.

How can you be sure you're drinking enough water? When your urine is clear (meaning diluted) rather than yellow. It is important to keep drinking after your workout. Weigh yourself before and after a workout. For every pound of water you've lost (come on, you don't think you just lost a pound of fat, do you?), you need to drink one pint (16 ounces, or two 8-ounce cups) of water to replace it.