The Mystery of Muscle Cramps

It can happen for no reason, it seems, taking you completely by surprise. And it can be excruciating. Suddenly, a muscle contracts violently, as if it had been prodded with a jolt of electricity. And it remains balled in a tight knot as painful second after painful second drags on. Cramps afflict 39 percent of marathon runners, 79 percent of triathletes, and 60 percent of cyclists at one time or another, said Dr. Martin P. Schwellnus, a professor of sports medicine at the University of Cape Town.

Cramps can occur during exercise, immediately after, or he said, as long as six hours later. Yet common as they are and terrible as they can be, no one really understands cramps. They are a medical mystery. “I would say, bottom line, there is no really convincing biological explanation for muscle cramps,” said Dr. Andrew Marks, a muscle researcher and chairman of the department of physiology and cellular biophysics at Columbia University College of Physicians and Surgeons. Medical textbooks skirt the topic, he added, often avoiding any explanation. And few scientists have studied cramps. But as anyone who has ever complained of cramps will attest, lots of advice is circulating on how to avoid them and lots of people — friends, coaches, doctors — think they have a solution.

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. But asked whether there are any rigorous studies to confirm this hypothesis, he said no. “We haven’t done the study yet,” he said. “We’re at the point of kind of connecting the dots.”

The third hypothesis is advanced by Dr. Schwellnus. He questions the electrolyte hypothesis because his studies of Ironman-distance triathletes as well as other studies of endurance athletes found no difference in electrolyte levels between those who suffered cramps and those who did not. DR. SCHWELLNUS proposes that the real cause of cramping is an imbalance between nerve signals that excite a muscle and those that inhibit its contractions. And that imbalance, he said, occurs when a muscle is growing fatigued. His solutions for cramps are to exercise less intensely and for shorter times, to be sure you had enough carbohydrates to fuel your muscles, to train sufficiently and to regularly stretch the muscles that give you problems. These recommendations are based on his recent study of Ironman triathletes, Dr. Schwellnus said. But while he advocates those practices, he said, they have not been proved in a rigorous study. In the meantime, some doctors have resorted to experimenting on themselves, devising their own explanations and cures.

Dr. Charles van der Horst, an AIDS researcher at the University of North Carolina, said he was stunned when his calf started to cramp without warning when he was running. The pain was almost unbearable, he said, and even when the muscle finally relaxed, it cramped again when he resumed running. “I started carrying a cellphone with me on long runs,” Dr. van der Horst said. When a cramp struck, he called his wife to ask her to drive out and get him. “I think I was getting calcium deposits or something,” Dr. van der Horst said. His solution was to massage his calves at all hours, pushing deep into the muscle. This seems to work, he said, explaining that it’s been a year now since he had a cramp.

Dr. Stephen Liggett, a professor of medicine and physiology at the University of Maryland, has a different solution. He got terrible cramps in his calf during yoga. The culprit, he decided, was the drugs he takes for asthma, which can diminish the body’s supply of potassium. He knew that potassium is sold over the counter. But because high levels of potassium can be dangerous, store-bought potassium supplements are not very strong.

Dr. Liggett’s solution is not one anyone who is not a doctor should try at home. Before he does yoga, he measures the potassium levels in his blood before and after taking what he describes as a hefty dose of over-the-counter supplement. Then he calculates how much additional potassium he thinks he needs, securing it from concentrated potassium tablets from his research lab — how much he declined to say. “I didn’t want to drink two gallons of Gatorade,” Dr. Liggett explained. He hasn’t had cramps since he began “preloading,” as he calls it, with potassium. But, he said, “I haven’t done a controlled trial.” Dr. Marks, for one, is not convinced by the evidence for any of the hypotheses, nor by any of the proposed remedies. What causes cramps? “I would say the answer to that question is still open to investigation,” he said. And, he added, he hopes someone takes it up.