Take a multivitamin pill to get zinc and magnesium. Massage the muscles. Drink plenty of water. Be sure to get enough electrolytes like sodium and potassium. Stretch before you start to exercise. No, stretch as soon as you finish. See a nutritionist to correct imbalances in your diet. See a trainer to be sure you are moving correctly.

Of course, Dr. Marks said, medical conditions can lead to cramps, including narrowed blood vessels, usually from atherosclerosis, or compression of a nerve, as happens in spinal stenosis. Cramps also can arise from hypothyroidism. And they can be a side effect of medications like diuretics, used to lower blood pressure, which can lead to a potassium deficiency that can cause cramps.

But, he and others said, those conditions do not explain the vast majority of cramps.

“You are left with the fact that cramping usually occurs in healthy people without any underlying disease,” Dr. Marks said.

There are three leading hypotheses about how to treat cramps and how to prevent them.

There’s the dehydration proposal: you just need more fluid. But, Dr. Schwellnus said, he studied athletes who cramped and found that they were no more dehydrated before or after a race than those who did not have cramps.

Then there’s the electrolyte hypothesis: what you really need is sodium and potassium.

Michael F. Bergeron, who directs the environmental physiology laboratory at the Medical College of Georgia, said the electrolyte hypothesis applies to a specific type of cramp that is related to excessive sweating. It occurs, he said, when the fluid that bathes the connection between muscle and nerve is depleted of sodium and potassium, which was lost through sweat. The nerve then becomes hypersensitive, Dr. Bergeron said.

“Usually you feel little twitches first,” he explained. “They last for 20 to 30 minutes and if you don’t do anything you can be in full-blown cramps.” Those cramps, he continued can move from place to place on your body, from one leg to the next, to your arms, stomach, even your fingers or your face.

The solution, Dr. Bergeron said, is to drink salty fluids like Gatorade (the company sponsors his research). He said he had prevented cramps in tennis players this way.