Andy Cousins limbers up with a few muscle stretches and then climbs onto a concrete banister in a Chicago park. He balances on his Adidas for half a breath -- and then launches into space, pinwheeling his 21-year-old body forward in a flip 10 feet off the sidewalk.

His feet touch down, and that's as far as he gets.

A security guard appears and tells Cousins and his crew to get out of the park.

"Okay, okay," Cousins mutters.

He nods to his four friends -- who call themselves the Aero crew -- and they take off, ambling toward a plaza across the street.

It's too bad. The new park, Cousins says, has "great topography" for parkour.

Parkour is an urban sport still unknown to most American teenagers -- and security guards. An import from Europe, it's a new way of bringing together the spring-loaded bodies of young males with stairways, park benches, the stuff of city blocks and suburban shopping malls.

Call it skateboarding, but without the skateboards -- a form of extreme gymnastics that swaps parallel bars and mats for fire escapes and concrete.

The sport was invented in the late 1980s by two suburban Paris teens, Sebastien Foucan and David Belle, who began experimenting with obstacle-course-style exercises taught to them by Belle's father, who had served in the military. Parkour (pronounced par-KOOR) translates approximately from the French "parcours," or obstacle course. Parkour athletes use whatever is around them -- stairways, benches, even rooftops -- as obstacles and springboards to vault and jump off of in a series of moves called "runs."

Foucan and Belle added their own techniques borrowed from gymnastics and the martial arts. By 1997, they had a complete repertoire, which they considered an art form, "the art of movement," as well as a band of followers, eight parkour athletes who called themselves Yamakasi (or "modern-day samurai").

Being a French sport, it even comes with a dose of philosophy. Participants aspire to "free flow," or achieve a state of mind over matter in which their bodies move over any obstacle in their path from point A to point B, vaulting railings, jumping over stairwells, running along walls like Spider-Man.

"When you're moving in this kind of way, it makes you realize the human body has no limits," Cousins says. "You feel like you can do anything."

In Chicago, Cousins's Aero crew is the only group doing parkour, according to the member rolls of www.urbanfreeflow.com. Urban Freeflow is a London-based group with a Web site that serves as the sport's hub, its message board and the closest thing it has to a sanctioning body. The site was launched last year and reports 16,000 daily visits; it offers parkour instruction, has a calendar of events and keeps a roster of traceurs -- as parkour athletes are known -- around the world, counting 3,600 subscribers.

After getting the boot from the park, Cousins and his buddies head to a nearby plaza to check out the lay of that land.

Aero member Homer Azari, 18, eyes a spotlight attached to an exterior brick wall. Grinning at his own audacity, he clambers up on a nearby planter to reach it. He gives it a tug. It holds his weight. So he pulls himself up until he's balancing about eight feet off the ground. He thinks for a moment, and then he hoists himself back down, takes a few fast strides and leaps from ground to planter, and then an athletic bound onto the spotlight. His feet touch just to deflect him back down to the planter, and then another bounce into a barrel roll of legs and arms.

Parkour remained little known until it was put on the map by the documentary "Jump London," televised in Britain last year. It showed parkour master Foucan leading a group of traceurs as they turned London landmarks into their own jungle gym, leaping from the HMS Belfast on the Thames and scaling the rooftops of the Tate Modern.

Interest in the sport "exploded," says Paul Corkery, founder of Urban Freeflow, who is better known in the parkour world as EZ.

Hundreds of British kids began copying what they'd seen in the film and searching out his Web site. (Urban Freeflow has since been incorporated and Corkery works full time promoting the sport.)

Along with it came parkour's first wave of injuries -- falls resulting in broken bones and the like, Corkery says. "You had kids going out thinking they could go out and jump off high objects. Very quickly they found out that to do so, you need to practice landings and how to roll and transfer the energy of the jump."

Before "Jump London," parkour had a few dozen devotees. Foucan, now 30 and living in the Paris suburb of Evry, tries to get at the nature of their creation and the meaning of free flow in an e-mail interview. "It's a mix of animal, water and Spiderman," he writes. "Gymnastics like track and field are a part of my Discipline but they're a sport with rules! Not enough place for creativities! Dance is more close the way! Feeeeeel!!!"

French filmmaker Luc Besson borrowed the sport and their name for a 2001 fictional movie, "Yamakasi."

Parkour made its way to London. Belle, who has since parted ways with Foucan, was filmed by the BBC pulling off heart-stopping stunts and jumps for a commercial titled "Rush Hour" that has since become a parkour cult classic. A "Jump" sequel is in the works.

Parkour purists say they are worried about where they see the sport heading -- emphasizing the tricks and jumps, but not the feeling.

Parkour is making its way into the United States, helped along by word-of-mouth on the Internet -- along with Urban Freeflow, there are a few other sites devoted to parkour, including one run by Foucan at www.parkour.com -- and by recent converts and images of the sport popping up in the media. Nike has used parkour to sell sneakers. Toyota hired Foucan to star in a parkour ad for its new Scion.

Cousins says he was hooked after seeing parkour on a TV news show several years ago.

He was into extreme sports such as snowboarding and freestyle cycling, and his brothers, who are on the Aero crew, competed in high school gymnastics. Cousins dabbled in gymnastics but wasn't crazy about the discipline it required.

Parkour, he says, tapped into his inner kid, who -- walking along an ordinary sidewalk -- is secretly itching to vault over barriers, swing from a street lamp and climb things.

"It's like when you're walking down a street and you see a sculpture, or you see a ramp leading up somewhere. You almost get the urge to go up there," he says. Parkour embraces that.

"It's really liberating. You're doing things other people can't do. Or think they can't ever do," he says.

Cousins, who is from Northbrook, Ill., will be a senior this fall at DePaul University, majoring in mathematics. He and his brothers Ryan, 18, and Will, 16, and the rest of the crew venture out to do parkour at least once a week during the summer. Any place with lots of obstacles and plenty of room will do. Millennium Park is good, but they get hassled by security guards. The campus of Loyola University is better. At home in suburban Northbrook, they go to the city park or school grounds.

Cousins resists the comparison of parkour to skateboarding. But he sums up its rebellious appeal this way.

"We can move like no one else can. There's no one [cops included] that can catch us on foot," he says.