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Is dehydration really detrimental to performance?

July 11, 2013

After doing a little research, which is generally a bad idea because you can find anything the Internet to support your view; I am happy to be able to celebrate my naivety 🙂

I have been running in the surprisingly hot weather and have seen lots of other runners with water bottles. I was going to get one but quite honestly I haven’t because I like to run without anything. No music, no wristbands, no jangling keys…but boy it’s been hot.

So I have just been drinking lots after a run when I am thirsty, not before when I’m not!

From RunnersConnect:

The current recommendation for hydration is four to eight ounces of fluid every 15 to 20 minutes of running. However, these recommendations were based on early studies conducted in the 1960’s which suggested that dehydration determines the body temperature response to exercise and thus, the development of heat-related illnesses.

However, more recent studies have now shown that dehydration, or rather a reduction in body weight due to exercise, is a normal part of exercise.

A recent meta-analysis of laboratory-based studies examining the impact of dehydration on performance resulted in the following conclusions:

  1. It was found that a reduction of body weight of 2.2% was not associated with a decrease in performance.
  2. It isn’t dehydration itself that is responsible for any decrease in performance, but rather not drinking in response to thirst.
  3. Drinking enough to satisfy thirst resulted in a 90% performance advantage compared to drinking below thirst and a 63% performance advantage over drinking above the thirst response.

The only symptom of dehydration is thirst and often, this thirst becomes overwhelming that the athlete is compelled to drink when fluid is available.

Furthermore, studies have disproved the claim that a reduction in body weight less than 2% results in impaired performance. For example, a recent study confirmed that Haile Gebrselassie lost 10% of his body mass due to dehydration during his world record marathon run in Berlin.

The results of this latest research show, for the first time, that drinking according to thirst is the superior hydration protocol to maximize performance.


The maximum rate at which the intestines can absorb fluid is, on average, about 600 mL (or 20.3 fl oz.) per hour. The kidneys can only excrete fluid at a rate of about 800 mL/hr in males and closer to 600 mL/hr for smaller females. If fluid is ingested above these rates, it will be retained and may cause a number of problems associated with hyponatremia.

Therefore, based on the latest research and findings, hydration for training and racing isn’t as complicated as we’ve tried to make it. Simply drink according to your level of thirst and you’ll be maximizing your performance while also keeping yourself safe.


1. Noakes, T. Waterlogged: The Serious Problem of Overhydration in Endurance Sport. Champaign, IL: Human Kinetics; 2012.
2. Rosner, MH, Kirven J. Exercise-associated hyponatremia.Clinical Jounal of the American Society of Nephrology, 2007;2(151-161).
3. Goulet, ED. Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure. British Journal of Sports Medicine, 2012.
4. Wyndham CH, Strydom NB. The danger of an inadequate water intake during marathon runningSouth African Journal of Medicine, 1969; 43(893-896)

From → Running Tips

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