But critics aren't convinced. Since the Carol Stream park opened in November, emergency call records show that 16 ambulances have been dispatched for trauma ranging from broken ankles and dislocated shoulders to a head injury.
In one instance, a 13-year-old girl fell on her neck and reported tingling in her arms and difficulty breathing.
The potential for devastating injuries concerns Gary Smith, director of the Center for Injury Research and Policy at Nationwide Children's Hospital in Columbus, Ohio. He sees the parks as a progression from the use of backyard trampolines, which nearly tripled the number of trampoline injuries in the 1990s, with 11 deaths.
The American Academy of Pediatrics, he notes, recommends against the use of trampolines other than in a supervised setting, such as in a gymnastics facility. It also warns against using trampolines as toys in the backyard and allowing children younger than 6 to participate.
"This sounds like a very large backyard," he said. "That would not be where I would want my child to learn how to use the trampoline."
The controversy stirs the debate over where to draw the line between reasonable safety guidelines and freedom of choice.
Operators say no activity is risk-free. All customers, and guardians for those younger than 18, sign a waiver releasing Xtreme from liability if they are injured or killed.
Trampoline parks are safer than backyard trampolines, Xtreme owner Eric Beck said, because each trampoline is bordered by other trampolines or by a floor on the same level. He estimates his facility's injury rate at two out of 1,000 customers.
"It's over 99 percent safe, not 100 percent safe," he said. "If you're not comfortable with the risk, don't do it."
After paying $11 for the first hour, Xtreme participants, whose average age is 16, are required to watch a three-minute video going over the rules. There are no shoes, no running or rough-housing. There's also a limit of one person per trampoline, with no double-bouncing, in which one person lands to bounce another higher in the air. Participants are encouraged to stay within their abilities.
Still, injuries happen. Central DuPage Hospital in Winfield, Ill., saw a noticeable increase in traumatic injuries after Xtreme opened, said Kristine Cieslak, medical director of the pediatric emergency room. She said the ER staff has treated numerous youths with broken legs and arms, and one with a fractured neck, fortunately without paralysis.
Parents and teens told her they didn't realize the risk.
Nationwide, almost 100,000 people go to emergency rooms each year for injuries in trampoline accidents, including those in gymnasiums and at home. Some other activities, like bicycling, basketball and football have far more injuries, Beck points out. But the U.S. Consumer Product Safety Commission, which tracks those numbers, does not calculate the rate of injury per participant.
Unlike amusement parks, trampoline parks are not regulated in Illinois by any state or federal agency. That's because the parks do not involve a moving apparatus, according to the Illinois Department of Labor.
Instead, review of proposed trampoline parks falls to municipalities, but they don't typically get involved in operational safety issues.
A leading critic is Mark Sohn, a former member of the U.S. gymnastics team who insures gymnastics facilities. He won't sell the coverage to trampoline parks because he says they don't have adequate training and supervision.
Most people, especially thrill-loving teens, have no idea of potential dangers, Sohn said.
By comparison, Sohn says, tumblers at a gymnastics club are taught individually and held, or "spotted," by a coach until they have developed each new skill.
"There's risk associated with everything, but this is a free-for-all," Sohn said. "In time, how many people are going to be quadriplegics or paraplegics?"
Jerry Raymond, co-owner of Sky High Sports, the other company expanding into the area, acknowledges the risks, but says further regulation isn't needed. Moreover, he touts the health benefits of participating in the park's organized aerobic classes or dodge ball.
On a recent afternoon at Xtreme, 17-year-old former Downers Grove South High School gymnast Jon Keslinke did flips off angled wall trampolines and landed with a grin on his face.
"I love it," he said. "It's everything that I want to do. You can experiment and do things you can't do outside."
He taught classmate Tracy Echert a back flip by holding the back of her shirt and helping her spin around, as coaches once taught him.
"It's scary," she said. "But it's fun."