Conventional wisdom among runners is that dehydration is to be avoided at all costs. After all, doesn't dehydration cause overheating? Doesn't dehydration often result in heat distress? Doesn't dehydration severely impair performance? Aren't runners who collapse near or at the end of a race severely dehydrated and should be treated with rapid hydration?
Most of the running community will answer these questions with a resounding "yes". This all seems very logical and commonsense.........but it is not true!
Over the past several years, the "dehydration is evil" theory has been disproved by Dr. Tim Noakes, one of the most eminent exercise physiologists. (Incidentally, Dr. Noakes is probably the only researcher in his field to have his own Wikipedia entry).
Dr. Noakes tested South African marathon and Ironman finishers in a series of studies over the course of several years. He determined that:
- Elevated body temperatures (a precursor to heat distress) and overheating were not tightly linked to dehydration.
- High core temperatures and overheating were closely related to running pace and to metabolic rates during racing. This makes sense as the faster or longer you run, the more heat you generate.
- Dehydration does not necessarily hurt performance. In fact, race winners often finished in a very dehydrated state and were more dehydrated than slower runners.
- A runner's level of dehydration is not a predictor of medical complications during or after the race.
Dr. Noakes concluded that dehydration is not a medical condition that automatically requires treatment; rather it is just a state in which there is a reduction in the water content in the body.
Muscle cramping that some runners experience during long races is commonly believed to be caused by dehydration. Runners suffering from leg cramps often take in fluids and salt to alleviate cramping.
Dr. Martin Schwellnus, a colleague of Dr. Noakes' at the University of Cape Town, asserts that there is no relationship between dehydration and muscle cramping. He believes that muscle cramping is caused by changes in the electrical signals sent to the tired muscle. Cramps are best avoided through proper training at race intensities. He advises to stop running and stretch the affected muscle as the most effective treatment for cramps.
Is dehydration the cause of runners collapsing at the end of a race? When Dr. Michael Sawka of the United States Army Research Institute of Environmental Medicine studied the issue, he concluded that the actual cause of collapse was the pooling of blood in the lower limbs after ceasing heavy exercise, combined with the sudden reduction in heart rate. Just lifting these runners' legs to a level higher than their head proved to be the most effective treatment.
In addition, a runner who drinks large amounts of water in an effort to avoid dehydration during long runs risks developing hyponetremia (a condition where the sodium concentration in the bloodstream fall dangerously low), which can be fatal.
What does all this information mean to us runners? What drinking strategy should we employ? We suggest drinking 3-4 ounces (2 gulps) every 10 minutes. Ingesting sports drinks especially during runs greater than an hour in duration provide both carbohydrates to muscles that are being depleted of glycogen and electrolytes lost through sweating.
Dr. Noakes concurs: "As long as athletes drink according to thirst during their efforts, they will develop neither severe dehydration nor over hydration". He recommends a maximum of 27 ounces (about 800 ml) per hour of running, much in line with our information.
© 2012 Savvy Runner Inc.
Bennett Cohen and Gail Gould are the Founders and Presidents of the International Association of Women Runners. For access to resources to help you reach your goals for running and racing, visit www.IAWR-Connect.com..