Calf cramps and their causes.

? I've experienced cramping in my right calf for years when I get to mile 12 of a long run or halfmarathon. The Web contains multiple references to E-Lyte Sport electrolyte replacement drink, which promises an end to cramping. Information I've read in the past seems to indicate that the causes of cramping remain uncertain and therefore I'm skeptical of a surefire remedy. I'd like to cease experiencing these calf cramps but I shy away from electrolyte overloading. After all, I use Gu and PowerBars, yet the cramps remain. What's your take on E-Lyte Sport?

Paul Dorr, Manhattan Beach, CA

The majority of research leads knowledgeable exercise scientists to conclude that exercise leg cramps are a result of deficient fluid, sodium and other trace minerals, and/or overheating of the body. Meeting fluid and mineral requirements would not be overloading. E-Lyte Sport may be an acceptable product. The Gatorade Sport Science Institute's publication has a well deserved, highly regarded reputation, and I advise you to read further about electrolyte replacement and muscle cramping there: www.gssi.com.

Earl J. Carstensen, MD, Aurora, CO

Your problem is common, as is the belief that electrolyte loss is responsible. Theoretically, loading with E-Lyte Sport or some similar concoction might minimize the losses and shifts, but I am unaware of any controlled studies looking at this drink and rates of cramping. If your kidney function is normal (and one would think that it is if you're running half-marathons) there should be no harm in giving the drink a try prior to long runs.

William M. Simpson, Jr., MD, Charleston, SC

I've also found that if a person's calcium intake is too low, especially when their phosphorus intake is too high, they may be vulnerable to calf cramping.

Sarah Harding Laidlaw, MS, RD, MPA, Glade Park, CO

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