Almost everyone has experienced it. You're blissfully drifting off to sleep, your body relaxed. Suddenly, your calf is clutched with an excruciating spasm — as if your leg was just jabbed with a butcher's knife.
The charley horse, or nocturnal leg cramp, is as common as it is unwelcome — a miserable, unexplainable affliction that has us, and doctors, wondering why the heck it happens and how we can avoid the next one.
Even the name "charley horse" is a bit of a mystery; its exact origin is unknown, but is rumored to be an old baseball slang word.
One thing's for certain — these cramps hurt.
"I've never had a baby," said Dr. Blake Boggess, assistant professor of sports medicine at Duke University's medical center, "but I can imagine that kind of pain, with your uterus contracting so intensely — that [charley horses] might be similar to that."
Nancy Gatlin, 77, of Winston-Salem, N.C., says she deals with nighttime cramps fairly frequently. Normally she gets them in her legs and feet, but recently they have struck both of her inner thighs, at the same time.
"It's really strange; it's hard to stretch out unless you can do splits," Gatlin said with a laugh. "[It] is the worst, they are quite painful."
Gatlin isn't alone in her pain. Doctors confirm that nearly every patient they see, if asked, say they've experienced a charley horse. So, shouldn't a health problem that's so widespread and torturous be a thing of the past?
"For something this basic and common, it still is hard to understand," said Dr. Neil Porter, a clinical neurologist at the University of Maryland Medical Center. "It isn't something that's going to require major medical intervention. ... The question is, how much research do you want done on you for just a cramp? If you ask people if they want a muscle biopsy, they are going to say 'no way.'"
Because nighttime cramps are short-lived and relatively harmless, doctors only have a collection of educated guesses as to why cramps happen, although, according to Dr. Dana Stearns, an emergency physician in the department of emergency medicine at Massachusetts General Hospital, "No one's given a good explanation."
The suspected cramp culprits are electrolyte imbalances and dehydration. Certain medications, like antipsychotics and blood pressure or diabetes drugs can act as triggers for the problem. So can exercise and sitting in some positions for too long.
Another clue is the fact that pregnant women and elderly people seem to get charley horses much more frequently, though people of every age and condition do get them.
Ultimately, doctors suspect the different physical triggers cause the same thing. Key minerals — sodium, potassium and calcium — all play a role in causing muscles to contract. When the levels of one or more of the minerals are depleted or changed, say, from lack of hydrating or from excessive sweating, muscle contraction can go awry.
What's actually going on in the muscle and nerve cells is a little harder to tell, according to doctors.
"It has to do with the excitatory and inhibitory pathways of the nervous system," said Dr. Doris K. Cope, vice chairman of pain medicine in the department of anesthesiology at the University of Pittsburgh School of Medicine.
She adds that, during nighttime cramps, the muscle cells' "relax" button is disabled, meaning that no matter how much we'd like to unclench our rock-hard calf, we can't.