I guessing you're problem is an electrolyte deficiency.
There are two ways to try to fix the problem, and my opinion is that it's best to do both of them at once. Every runner has different electrolyte needs. Per hour on a run your body will exhaust a certain amount of salts, and each person goes through them at a different rate. Lack of salts in your body is a big problem because it means that you cannot retain enough water to keep yourself hydrated, and you end up getting cramps.
The big mystery is finding out what the correct balance is for your body. Professional runners spend a great deal of time figuring it out, which is why during marathons, at designated water stops, they each have a different bottle. Each bottle contains a different mixture of electrolytes and carbohydrates. There is a company called Hammer Nutrition which sells these little pills that you can add to water. They are called endurolytes on their website. The idea is that through experimentation you will be able to eventually find your right balance.
Another thing to do that will greatly help is to push up the weekly mileage just a bit so that your long runs are no more than 1/3 your total weekly mileage. So if you run 30 miles a week your long run should only be 10 miles. By pushing up the mileage during the week, you will condition your body do a point where it is not shocked by the sudden increase in mileage. Gradually, you will extend your threshold and reduce cramping.
Hope that helped a little.
|