The first time he saw David Belle, Mark Toorock knew he had to become a traceur.

Belle's cat-like balancing acts, his eye-popping feats of agility, his sheer strength ... "What I saw, frankly, was a guy with superhuman capabilities," Toorock told FOXNews.com. "[He] was doing all these things without pads or a wire."

That was back in 2002, when parkour — an extreme sport popularized in France during the 1990s in which participants run, jump and flip from Point A to Point B as efficiently as possible — was relatively unknown outside of Europe.

Now the obstacle-based urban sport appears ready to hit the American mainstream, with a new MTV series ("Ultimate Parkour Challenge") set to debut later this year, and with dozens of parkour clubs sprouting up across the country.

Parkour, based on a type of a military obstacle-course training called parcours du combatant, has flourished online — more than 100,000 videos of traceurs (or traceuses) can be seen on YouTube. Its also been featured in several commercials and action movies, including The Bourne Ultimatum and Casino Royale.

But it is not without its dangers. Most traceurs wear no protective gear — and serious accidents can and do occur, as evidenced by amateur online videos and European news reports. One orthopedic surgeon told FOXNews.com that the activity is a great way to exercise, but it also can result in sprains, broken bones and torn ligaments.

It all traces back to Belle, 39, a French actor and stuntman trained in gymnastics and martial arts. He is largely credited with developing parkour in Paris' suburbs after he served briefly in the French marine infantry. His videos are legendary and inspirational within parkour circles, with acrobatic maneuvers few can match.

Toorock says he saw one of the videos, and "I very quickly got hooked. I said, 'That looks like fun and something I could be a part of.'"

Three years ago, Toorock, 38, opened Primal Fitness, a gym in Washington, D.C., where he trains men and women of all ages to become parkour pros during 6-week-long "boot camps." He also runs AmericanParkour.com, a national meetinghouse for traceurs and traceuses.

"The boot camps consistently sell out," Toorock said. "And we have 52-year-old ladies coming in and 60-year-old guys as well."

About 99 percent of the videos on parkour Web sites are of men aged 14 to 24, Toorock said. But inside his gym, classes are composed of up to 30 percent women and packed with young professionals. Police officers, federal air marshals and members of the Department of Homeland Security have also participated in the classes, he said.

Toorock, citing Chicago, Miami, Houston, Dallas, San Francisco and Seattle as budding parkour playgrounds, estimates that up to 7,000 people in the U.S. practice parkour on a regular basis, with another 10,000 doing so occasionally. On June 6, he said, the sport celebrated its first National Parkour Day, with roughly 600 participants in cities nationwide.

"Part of it is a very social thing," he said. "You can meet up with other people, share ideas. There's a lot of motivations as to why people do this, and a lot of it is people who want to make a positive impact."

Toorock scoffs at suggestions that the sport is a reckless collection of stunts strung together without meaning.

"We're not rebelling against anything and we're not breaking any laws," he said. "What we're doing is bucking the notion that it's somehow not acceptable in our society for adults to play."

But most physical play has its dangers — and parkour practitioners risk serious injury — and even death.

In 2005, Alex Leatherbarrow died while leaping a 6-foot gap between buildings in Wantage, England, reportedly in an attempt to copy jumps he'd seen in parkour films. Just two months ago, a 16-year-old girl was seriously injured after she fell through a skylight while reportedly imitating the sport on rooftops in Fife, Scotland.

Dr. Jonathan Chang, an orthopedic surgeon in Alhambra, Calif., said anyone interested in taking up parkour should get into "reasonable condition" first.

"There's not a lot of literature on this particular type of activity, but basically what you can expect out of this are injuries similar to others in stop-and-go sports like volleyball, basketball, tennis and soccer," Chang said, adding that most injuries would likely stem from the jumping aspect of the sport.

Ankle sprains and fractures also are likely, along with long-term injuries like tendinitis and cartilage tears. And although virtually no traceur wears pads or protective equipment, Chang recommends wrist and elbow guards, along with knee braces and a helmet.

"Consider that this is mostly an urban phenomenon," Chang told FOXNews.com. "This is a good way to get a great deal of exercise in a short period of time for those who are cut out to do it. It can be a very good way to burn a lot of calories quickly."

Toorock himself is currently nursing a sore shoulder — and possibly a torn ligament — from a combination move called a "Tic-Tac" into a dive roll, in which an individual jumps on a surface like a wall, then jumps off in another direction, finally landing into a roll, similar to an unspooling ball of yarn.

"But doing that out of a Tic-Tac is a new combination for me," Toorock said. "I put down a pad, but apparently the pad wasn't enough. You should always practice with safety in mind, but at the same time, you have to try things to expand your boundaries."