Sports Science Update: Dehydration Does Not Cause Muscle Cramps

New study explodes old myth.

Written by: Matt Fitzgerald

Ask 100 runners what causes muscle cramps during exercise and at least 60 of them will say it’s either dehydration or electrolyte depletion or both. This idea goes back more than 100 years, yet it has never been supported by well-designed scientific studies. In fact, most studies have found that hydration and electrolyte levels are higher in athletes at the moment a cramp strikes than they are in non-cramping athletes who have performed an equal amount of exercise.

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One challenge to proving or disproving the dehydration theory of cramping is that it is very difficult to study cramping in a controlled manner. As Ross Tucker pointed out in The Runner’s Body, “Perhaps the greatest problem affecting our understanding of muscle cramps is that no one has yet created a laboratory protocol in which scientists can deliberately induce muscle cramps in a controlled, reliable manner.”

Until now. In a study newly published in Medicine & Science in Sports & Exercise, researchers at North Dakota State University used electrical stimulation to induce muscle cramps both before and after subjects cycled indoors in a hot environment until they were 3 percent dehydrated. The objective was simple: To see whether less electrical stimulation was required to induce cramping in the calf muscles when subjects were dehydrated than when they were hydrated.

In fact, there was no difference in the amount of electrical stimulation required to induce cramping before and after dehydrating exercise. This is very good evidence that exercise-induced muscle cramping is caused by a fatigue-related factor rather than by dehydration or electrolyte depletion, as fatigue is always present when cramping occurs “in the field” but was removed from the equation in this study.

Add this finding to already existing evidence against the dehydration/electrolyte depletion theory, such as the fact that cramps always occur in individual working muscles instead of throughout the body, as one would expect if they were caused by dehydration, and the fact that cramps usually go away when an athlete stops moving and stretches or massages the muscle, which measures do not affect dehydration.

[sgi:MattFitzgerald]

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