The patient was a healthy young woman who came into a Washington area emergency room this year because of severe heel pain, which turned out to be a potentially serious injury known as "compartment syndrome."

The syndrome is typically caused by high-impact accidents, like something involving a motor vehicle. The patient had not been in a car accident. The patient had been in Zumba.

"I have seen some interesting things," says David Pontell, the podiatrist who ultimately treated the injury. "That was one of them."

People can get injured doing a lot of things that are dangerous or physically punishing. Or they can get injured doing Zumba. Zumba is not inherently dangerous. Its injuries are not any more prevalent than those from any other physical activity. They are just more embarrassing.

"By the end of the class, I was on fire, and not in a 'Hoo-hoo, I'm hot and sexy!' kind of way," Tonya Green, 32, says ruefully. She discovered, through a Zumba class, that she had something called snapping hip syndrome. " It was a salsa movement. I Zumba'd my hip out, real good."

Some 12 million people worldwide now do the cardio dance bonanza that is Zumba.

"We see a lot of ankle strains," says Rajeev Pandarinath, an associate professor at George Washington University's Department of Orthopaedic Surgery. "There are a lot of lateral moves in Zumba."

"I've seen some sprains; I've seen some stress fractures," says Dr. Elizabeth Delasobera at Georgetown University Hospital's ER. The reasoning, she speculates: A novice starting a running program will probably jog only two or three times a week, for 15 or 20 minutes. Because running is kind of awful. But somebody who starts a Zumba program? "They're Zumba-ing five days a week."

Maybe her patients are Zumba-ing five days a week. Our Facebook friends are Zumba-ing seven days a week. They are Zumba Toning and Aqua Zumbaing and watching Zumba TV and taking mass Zumba classes in at a fitness studio lit by a disco ball.

"It blows the paradigm," says Dr. Pamela Peekes, Discovery Channel medical correspondent and Zumba fan. "You could do it naked. You could do it half-naked. You could do it alone. You could do it with 65,000 other people."

Zumba classes are populated by people who are either amazing dancers or believe themselves to be amazing dancers. Zumba is the kind of freeing experience that causes its attendees to fling themselves about in delirious passion, so moved that they do not even notice when they have Zumba'd their own bodies into unnatural and inadvisable contortions.

"We get people being so enthusiastic," says Joy Prouty, who works for Zumba, training other Zumba instructors. She preached safety first, but there is little that even a conscientious instructor can do for a determined participant.

"It was embarrassing to talk to my doctor about it," says Karen Montague, a 40-something who injured her back. But when she mentioned it to the nurse, the nurse wanted to know where she could find a good place to Zumba.