The Weight of Water
Recently, John Hanc wrote a short article on how much water you should really drink to avoid overhydration and dehydration. It was published in the August '07 issue of Runner's World as part of a major article on Beating the Heat when running. Here are the goods:
Drink too little, you worry about dehydration. Drink too much, you worry about hyponatrmia (low blood-sodium levels). Lisa Bliss, M.D., ultrarunner and medical director of the Badwater Ultramarathon, has personally experienced the effects of both.
In 2004, Dr. Bliss ran Badwater and, in the 125-degree heat of Death Valley, became hyponatremic. "You're sweating so much and everyone's telling you to drink," says Dr. Bliss. "I kept drinking, and when I finally hopped on a scale, I'd gained 9 pounds. I was dizzy and disoriented." Fortunately, the solution for Dr. Bliss was simple. "All I had to do was stop drinking," she says. She kept running, and the symptoms went away as her body shed the excess water through sweating and urination-allowing her to finish in 15th place overall.
"I kept drinking, and when I finally hopped on a scale, I'd gained 9 pounds. I was dizzy and disoriented."
Weighing in during the course of an event helps ensure you aren't gaining weight (a sign of overhydrating) or losing too much weight (dehydrating). Of course, we're not suggesting you train with a scale. But weighing yourself before and after runs is the best way to find out if you are taking in the right amount of fluids. That's the central point of the American College of Sports Medicine's new 2007 exercise and fluid replacement program." To estimate your fluid needs, weigh yourself naked before and after a hard one-hour run. Convert the amount of weight lost to ounces to figure out your sweat rate per hour-so a loss of one pound means you s weated about 16 ounces of fluid. In this case, going forward, you would try to replenish fluids at a rate of about 16 ounces per hour.
If figuring out your sweat rate is too much work, the ACSM guidelines suggest drinking anywhere from about 14-27 ounces per hour, with the higher end of the range applying to "faster, heavier individuals competing in warm environments and the lower rates for the slower, lighter persons competing in cooler environments." When you're out for more than 30 minutes, choose sports drinks over water, since the carbs and electrolytes they contain help you stay energeized and better hydrated during longer runs.