After seven days of a heat wave -- the longest since 2002 -- with days of record-breaking temperatures, it became more important than ever to realize that all athletes must stay well hydrated. If you have a stomachache or a headache, or even are feeling lightheaded, be sure to take precautions as it can be the onset of dehydration or heat stroke.

Maintaining proper fluid levels is extremely important during exercise. Some research indicates that you should drink 50 percent more than it takes to satisfy your thirst. If you exercise without fluids, especially in the heat, the stroke volume -- the volume of blood pushed out with each heartbeat -- declines. That can result in a decrease in the cardiac output, which is the amount of blood pumped by the heart.

Your heart rate will then drift upwards, your oxygen uptake will increase, and your temperature will go up. Therefore, it is most important to keep hydrated to prevent injury to your heart's function. Since most of our body weight is water, it is still one of the best fluid replacements.

If you don't drink enough, your heart and the rest of your body will not get enough blood and oxygen. At least one hour prior to your exercise workout, you should drink 8 to 10 ounces of water and continue to drink the same if you plan to exercise for more than an hour (then every 20 to 30 minutes with continued exercise).

Try to avoid exercising during the warmest hours of the day. Wear a hat and light-weight, loose-fitting clothing, take frequent cool showers or baths and stay in air conditioning as often as possible to help lower the body temperature.

If you feel uncomfortable, put wet towels on your body, look for a cooler location and get out of the sun. An estimated 1,000 Americans die each year from heat related illnesses that could be prevented by controlling your body temperature. And remember the magic fluid -- water.

Dr. Robert Weiss is a Fairfield native and has a sports-podiatry practice in Darien. He is a former marathon runner and was a member of the Medical Advisory Committee of the 1984 and the 1988 Olympic Trials.