Hydration: The Key to Exercise Success (cont.)

Hydration in the Heat

"Staying hydrated is fundamentally important to a successful summer exercise regimen, in fact, for any activity," says Survivor consultant Adrian Cohen, MD, of Neutral Bay, Australia. As the medical advisor for many reality shows, including Survivor and Eco Challenge, Cohen has seen firsthand the havoc that dehydration can wreak on performers and performance. "Whilst we tend to focus on hard, sweaty workouts and long jogging sessions, even a brisk walk or a scratch basketball game in the hotter weather puts demands on the human body, and without the 'fuel' (water) the engine runs dry," says Cohen, author of several books including Survivor First Aid.

Successful, balanced hydration starts with prepping yourself for exercising in the heat, says New York City-based sports medicine expert Lewis G. Maharam, MD. "Take 10 days to two weeks to get used to hot weather, building workout intensity and duration gradually," he says. Engage in higher-intensity activities during cooler morning hours and do easier work during the heat of the afternoon, he suggests.

Choosing Your Hydration Fluid

If you are not running a race, "the rule of thumb is to drink 8 ounces of a sport drink or water possibly every 20 minutes," says Maharam, who advises the ING New York Marathon. No more, no less. "If you are exercising less than 40 minutes, water is fine, but for anything over 40 minutes, you want a sports drink that has sugar or salt in it because this helps you increase the fluid that goes into the body. Most sports drinks contain the equivalent of an "active pump" that gets more water into the body faster than the unassisted process -- simple diffusion of water -- would have.

When choosing a sports drink, look for salt and sugar on the label and choose a flavor that you like. While shoppers may be bombarded with vitamin-infused beverages, Maharam says added vitamins are useful for recovery and post-event muscle soreness -- not for hydration the day of the event.

It's also important to replace the fluid you lose during exercise, he says. Weigh yourself right before and after workouts and for every pound lost, drink eight ounces of fluid.

Moreover, "step out of bed every morning and onto the scale, and if you're anywhere from 1% to 3% lighter than yesterday, rehydrate by drinking eight ounces of fluid for each pound lost before training again," he says. "If you are between 3% and 6% lighter, rehydrate and back off that day's training intensity. And if you lost over 7%, get to the doctor."

Dehydration is somewhat insidious, adds Cohen. You can't always tell when it's starting.


"Most people are chronically dehydrated."

"Humans don't have a 'fuel gauge' like your car, so there is no way to tell if you're full or even approaching empty, and thirst is typically a poor guide," he says. Early signs of dehydration may include poor concentration, headache, and inability to think clearly.