This is another in an occasional series of SNEWS® Health Notes reports that will take a look at one or more recent pieces of research studies or reports about health, fitness, physical activity and wellness. We'll focus on news you can use and present results in plain English, without all the techno-garble that can make many research studies seem overwhelming to read, let alone understand and explain to somebody else. Let us know what you think, what you would like to see, and how you'd like to see it!
When it came to drinking during exercise, we used to say, drink, drink, drink…. You can't get enough fluids when you exercise and you won't feel thirsty until you're already dehydrated. Until, of course, the world discovered a person can indeed get too much, sometimes with fatal consequences in the form of "hyponatremia," or a low blood sodium content through dilution from too many fluids that don't also replace electrolytes.
The debate has raged for the last few years about how much to drink and when and how that is affected by type of exercise, environmental conditions and each person's individual needs. With that in mind, the venerable American College of Sports Medicine (www.acsm.org) has just issued a new "position statement" titled "Exercise and Fluid Replacement," replacing the 1996 paper that had been the last word. With this new statement, the non-profit sports medicine and exercise research and education group -- the largest in the world -- has issued what for now should be the definitive word -- one steeped in science. The panel of highly placed scientists and researchers reviewed, according to the statement, more than 150 pieces of definitive research on the topic dating back more than two decades and included two pieces dating back more than 50 years.
The nine-page piece, not counting several pages of reference listings, lays out in exact detail the background of the issue, as well as effects of hydration, effects on performance of insufficient hydration, variables, health issues and, of course, recommendations for before, during and after exercise. You want charts and statistics? You'll get 'em. What you won't get are specific amounts to cite since they can vary so widely. There are some ranges, issued in milliliters per kilogram of body weight, but the basic message is to not drink more than you need, but rather to only match losses. Using a marathon runner as a guideline -- since that is the situation where most of the hyponatremia cases have surfaced -- the researchers do say that "a possible starting point" is for runners to drink what they feel they need between about 0.4 liters per hour to 0.8 liters per hour (or 13.5 to 27 ounces per hour), with the higher rates for faster and/or heavier individuals in warm environments and the lower rates for slower and/or light individuals in cooler temperatures.
The research summarizes the need to match losses with drinking, to pre-hydrate so an exerciser starts a workout hydrated, to monitor pre- and post-exercise weight to assess losses or gains, to use electrolyte solutions under certain circumstances to avoid blood dilution, and to replace losses fully when a workout is complete.
So what? Although much of the discussion gives outdoor examples, indoor exercisers should also take heed. Indoor areas can be warm and dry and can suck sweat from a person, although the sweat could evaporate quickly, leaving the exerciser thinking he or she is not becoming dehydrated. Still, drinking till you are swimming is not the best advice either. Giving advice on hydration can and should be part of any training information delivered to consumers.
For the scientifically minded: If you want to read all the charts and details or print out the statement, click here. It appeared in the February 2007 issue (Vol. 39, Issue: 2, pages 377-390) of Medicine & Science in Sports & Exercise, the official journal of the American College of Sports Medicine.