Q. Could you explain how dehydration might cause muscle cramps? Coaches often say NOT to drink water before strenuous activities to prevent cramps. Isn't that a contradiction?

A. We don't know for sure what causes muscle cramps, but they do occur commonly in hot weather conditions, so dehydration is a consideration. There is some speculation that a disturbance of electrolytes, the charged ions such as potassium in the bloodstream, contributes, but this has not been proven except in unusual circumstances. If an athlete trains in a hot, humid environment, dehydration is a serious concern. Water intake should be high throughout the day, not just prior to exercise, to avoid this complication. For exercise, liquid intake should be water or a "sports drink" which is fairly dilute, as concentrated drinks like juice or soda will cause cramping. Exercising at cooler times of the day and wearing light, porous clothing will also enhance cooling.

http://kidshealth.org/teen/safety/first_aid/dehydration.html

http://www.nlm.nih.gov/medlineplus/ency/article/000982.htm

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