Crrraaammps!

They're real teeth-gritters, but fortunately, easy to cope with on the trail.

"Experienced, fit people get cramps all the time," says Edmund R. Burke, Ph.D., of the University of Colorado, Colorado Springs, and author of Optimal Muscle Recovery: Your Guide to Achieving Peak Physical Performance ($14.95; Avery Publishing Group, 1999; 800-548-5757). "That's because they underestimate how much they're exerting themselves and end up dehydrated, over-fatigued, or with electrolyte imbalances." The unfortunate result can be an instant knot of pain that stops you dead in your tracks.

A cramp is nothing more than a muscle contraction gone bad. Though your muscles flex and relax hundreds of times a day without incident, occasionally one will lock in a sustained contraction, called a spasm. The exact cause is somewhat of a medical mystery, but prevailing wisdom points to simple dehydration. When your body isn't properly watered, two things happen:

First, since water is a component of blood, as the water in your system decreases, so does your blood volume. Think of your blood as getting thicker, like sludge. Since your blood delivers oxygen to your muscles, less blood to go around means less oxygen getting to your muscles. The result is prime cramp conditions.

Second, your sweating may cause an electrolyte imbalance. To properly contract and relax, your muscles rely on a carefully balanced ratio of electrolyte minerals (sodium, potassium, magnesium, and calcium). Spend a hot day climbing switchbacks and you'll lose a good bit of sodium through your sweat. Unless that's replaced, the ratio will be out of whack, which can cause muscles to contract whether you want them to or not.

Another culprit behind cramps is muscle fatigue, which can happen to fit or unfit people, especially when they try a new activity. "When you're fit, your cardiovascular system is well-defined to bring oxygen to the specific muscle fibers you typically use," Dr. Burke says. 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. "No one really knows why, but cramps can happen hours after you've finished an activity," says Dr. Burke, and often they occur in the middle of the night.

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.

Stretch. 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."

Rub. While you're stretching the muscle, take both hands and lightly massage the sore spot. "This will help unlock the cramp," says Dr. Burke.

Drink. The cramp won't stay unlocked very long unless you treat the underlying cause, he warns. "If possible, drink a sports drink to hydrate your body and to balance your electrolytes. If you don't have that, drink plenty of water." If you suffer from frequent, persistent cramps, see a doctor. There may be a more serious underlying cause.

CRAMP PREVENTION

To prevent your agony from returning, treat your muscles right.

Go with handless hydration. "If your water bottle is tucked away in your pack, you're not drinking enough," says Dr. Burke. Instead, invest in a hydration bladder with a bite valve so you can sip steadily throughout the day.

Drink smart. Buy a powdered sports drink that you can pack easily and mix during breaks.

Eat for performance. "It's crucial to get enough potassium, calcium, and magnesium," advises Dr. Burke. Be sure to work nonfat powdered milk, lowfat cheese, whole grains like bulgur, legumes (lentils are ideal), and dried fruits-especially bananas-into your trail diet.

Take your vitamins. If your muscles are relentlessly sore, try taking supplements. Dr. Burke recommends 400 milligrams of calcium and 800 milligrams of magnesium a day.

Train properly. If you're going to be hiking in the mountains, spend some time on your local hills a few weeks before the trip.

Stretch. Last but never least, take at least 5 minutes to stretch your muscles before and after a good hike.