They are skateboarders without skateboards, urban acrobats who scale walls, hurdle mailboxes and leap between buildings in stunts that might give Spider-Man pause.

Practitioners of parkour, a daring pastime born in the streets, have long seen public spaces as their playground, and parkour as the ultimate rebel's game, one with no rules, league, equipment or winners. It started in France (the name is derived from the French word for "course") and has spread around the world: Gaza, Tokyo, Rome and Miami are parkour towns.

One thread binds them all: parkour takes place outdoors. Bringing it inside, purists argue, would be like asking swimmers to perfect the breaststroke on grass.

But now, parkour has grown up, traded the pavement for padding and turned into a big business.

YouTube videos have helped parkour spread globally and it is being brought into gyms, like this one in New York. Emily Berl for The New York Times

Parkour gyms have opened all over, from California to New York to Britain and Sweden, featuring juice bars, private classes and children's birthday parties that cost $450 (cake not included). Specialized apparel companies sell tailored gloves for $34.50 and shoes for $60. An international organization offers special parkour insurance policies and charges $295 for teacher certification courses.

"Parkour is definitely blowing up," said Shem Rajoon, 27, an owner of Bklyn Beast, a parkour gym in East Williamsburg, Brooklyn, that opened this year. "I see it becoming something

very mainstream."

While the gyms' owners say they are broadening the activity's appeal, and making it safer in the process, hard-core enthusiasts say parkour's renegade soul is at risk.

"If you limit parkour to the indoor setting, you effectively nullify its very point," said Dan Edwardes, 37, author of "The Parkour and Freerunning Handbook." "The prevalence now of 'parkour gyms' in some countries, particularly the States, is worrying, as it means within a few years parkour will not exist anymore in

its original form."

Parkour's popularity has boomed in the YouTube era, as daredevils across the world record themselves leaping, and sometimes crashing, in a digital game of one-upmanship. Kudos go to the person who most creatively turns a parking meter into a diving board, a wall into a ladder.

The gyms, with their padding and liability waivers, offer a more sanitized version of the urban landscape. Many gyms are decorated with urban costumes, adopting indoor graffiti, scaffolding and handrails to mimic the outdoors.

On a recent Saturday at Bklyn Beast, children and adults leapt across a purple, springy floor, launching over vaults with abandon. They climbed fire poles and swung from monkey bars in front of walls tagged with spray paint.

Elizabeth Bellis Wolfe, a 29-year-old lawyer, said she found parkour to be a far more exciting workout than another session on the treadmill.

"It's just scary enough that you're thinking about being scared and in pain, but not so scary that you don't want to do it," she said.

But as with any subculture on the verge of gaining wider popularity, purists scoff at what they see as the commodification of their beloved pastime. They argue that the gyms, with their foam pits and soft floors, are spoon-feeding tricks to the public, dumbing down the jazzlike improvisation that is central to parkour.

"It's about using what is there and being creative with the space in front of you," said Kaspar Schroder, 33, a Copenhagen filmmaker who directed the 2009 parkour documentary "My Playground."

Many gym owners say they encourage their members to practice parkour inside and outside. And there are signs that even some hard-core parkour enthusiasts have taken to the indoors.

In June, New York hosted the seventh annual PKNY Jam, a weekend-long event that brings together enthusiasts from across the country. This year, for the first time, it also included an indoor session at Bklyn Beast.

Groups are also looking to capitalize on the trend. Red Bull started an annual freerunning contest in 2007. Video games like Assassin's Creed and Infamous feature characters performing parkour tricks.

The World Freerunning and Parkour Federation has seen increasing interest in its certification program, said Victor Bevine, one of its founders.

On a recent afternoon spent vaulting over chin-up bars in a Lower Manhattan park, Vanya Prokopovich, a 20-year-old lab technician from Ann Arbor, Michigan, extolled outdoor parkour.

"You feel free, and you feel such happiness," he said. Then he added: "You just have to be close to the concrete. Inside, it doesn't feel as natural."

The New York Times

(China Daily 09/08/2013 page9)