BOULDER, Colo. — Slacklining has achieved the recognition that assures its arrival as an outdoor sport: it has been banned by officials at some of the colleges and parks where the test of balance is popular.

The formerly little-known training technique devised by rock climbers is akin to tightrope walking — except the "rope," usually 1-inch wide nylon webbing, isn't so tight. This means that the line can sway wildly with the slightest misstep.

That's why slackliners normally practice just a few feet off the ground, stringing a line over a grassy stretch between trees. But some of the best and boldest slackliners perform hundreds, even thousands, of feet off the ground on lines anchored to rock walls.

"I thought it was kind of crazy, but it was kind of cool, too," said Kate Vander Wiede, an engineering student at the University of Colorado who saw a slackline set up at a rock climbing gym a couple summers ago. She went back two hours a day for three weeks until she had mastered walking across it without falling.

Wiede slips off her shoes and hops on a slackline strung about waist high between two trees at a public park in Boulder. Her arms outstretched, she walks slowly about a dozen feet in one direction, then delicately turns around and walks back.

"It's almost like meditation. You get on a slackline, all you think about is the next step," Wiede said.

But as slacklining grows in popularity, with clubs popping up from Haverford College in Pennsylvania to Arizona State University, not everyone is taking such a meditative perspective.

Citing safety concerns and possible harm to trees, University of Colorado officials banned slacklining on campus this year after dozens of students started showing up at slacklines strung across campus quads.

"Look, we're not trying to be killjoys here," said CU spokesman Bronson Hilliard. "You simply, as an institution, can't accommodate every single fun thing kids want to do when safety and environmental factors come into play."

Slackliners insist the activity is no more dangerous than skateboarding or bicycling, and that properly attached slacklines, which include pads, don't hurt tree trunks.

"They just shove off what they don't understand," said Scott Rogers, a CU philosophy and engineering senior who sets up regional slacklining events and once crossed a slackline 2,900 feet off the ground in Yosemite National Park in California. Don't worry. He wore a safety harness and was tethered to the line.

Rogers volunteered to talk with campus officials about allowing slacklining at CU, but his hopes are dim. University slackliners gather instead in backyards or at public parks off campus, where authorities haven't told them to stop.

With time, slackliners say, officials will relax. At Baylor University in Texas, slackliners say they had to keep a lookout for police a year ago. Now, officials are used to seeing barefoot students stepping across lines tied to trees.

"At first teachers would stop and ask whether we had permission from Student Life, and of course we just lied our butts off and said we did. But now they just walk on by," said Baylor junior Jordan Ryan. "There's only one cop now we try to avoid."

Slackliners say the activity originated in Yosemite in the 1970s with rock climbers looking for something to do during campground down time. The first slacklining, the story goes, started on chains strung between posts at a popular Yosemite campsite.

It didn't take off until about five years ago, when slackliners started posting videos online showing their feats — flips or yoga poses sometimes high in the air with landmarks such as the Golden Gate Bridge in the background.

Then companies started selling ready-made slackline kits, saving novices from having to build their own using rock climbing gear, and all of sudden the activity started popping up on campus quads and in public parks.

"It grew out of boredom. (The climbers) thought of it as a fad. Now it's everywhere," said Maria Quinones-Phiegh of Los Angeles, who started the Slackline Brothers Inc. equipment company with her husband in 2003.

Quinones-Phiegh says the sport is still going through a "bad-boy phase," with officials unsure what to make of it. But she says people are starting to come around.

Officials in Salinas, Calif., adopted pilot slackline park regulations in April after seeing a demonstration and hearing from activists. A similar pilot program was adopted in August in San Luis Obispo, Calif.

Slackliners expect more parks and campuses will embrace the activity. Andrew McCallister, a senior at the University of Arizona, says that when he started college, few had heard of slacklining. Now a couple dozen students slackline regularly on campus, with little bother from officials.

"It's almost like an addiction," said McCallister, who slacklines at least once a week. "I don't think it's something that's going to disappear into the wind."

ON THE NET

How to slackline: http://www.slackline.com

Find a slackline group:

http://www.facebook.com/pages/Slackline-Radio/5663333049‥;/group.php?gid=2208