Another culprit behind cramps is muscle fatigue, which can happen to fit or unfit people, especially when they try a new activity. So when you do something new, like hoofing it up a mountain when you're used to hiking the plains, you use different muscle fibers and your cardiovascular system doesn't work as efficiently. That's a prescription for muscle fatigue and cramping. The odd thing is that while activity causes cramps, cramps don't always occur during activity. In fact, lots of folks don't cramp up until they're nestled in their sleeping bags.
Cramps can happen anywhere in the body, though they have a particular affection for the calves.
Regardless of where or when a cramp strikes, treatment is the same. Straighten out the body part that's cramping, and gently stretch the muscle, says Dr. Burke. You also may want to try applying a little pressure to the affected area. If the cramp is in your leg, for instance, stand up to stretch and put your weight on it. While you're stretching the muscle, take both hands and lightly massage the sore spot.