Trampolines can be more dangerous than you think, according to a new study out of Indiana University School of Medicine. Researchers found that between 2002 and 2011, there were nearly 289,000 emergency room visits due to trampoline accidents that caused fractures and broken bones.

The study, which used data from 100 hospitals nationwide, was one of the first to review fractures related to trampoline use across the nation. Over the course of 10 years, trampoline injuries cost upwards of $1 billion in emergency room visits. “We are inundated with injuries,” Dr. Randall T. Loder, chair of orthopaedic surgery at the Indiana University School of Medicine and lead author of the study, said. “Kids need to be healthy and active, but this is not the way to do it.” Loder decided to do the study after he witnessed an increase of trampoline-related injuries during his time as a surgeon in the ER.

When you were a kid, you were probably super excited when you got to jump on a friend’s trampoline. But the American Academy of Pediatrics (AAP) has been warning parents to avoid buying trampolines since 1999. Though the AAP has noted that trampoline injury rates have been decreasing in the past decade, experts remain concerned about their potential risks. “Pediatricians need to actively discourage recreational trampoline use,” Dr. Michele LaBotz of the AAP said in a statement. “Families need to know that many injuries occur on the mat itself, and current data do not appear to demonstrate that netting or padding significantly decrease the risk of injury.”

According to the AAP, 75 percent of these injuries occur when there are multiple people jumping on the trampoline. Typically the smallest or youngest children are most vulnerable to injury — 48 percent of injuries in this age group end up as fractures or dislocations. Loder’s study pointed out that the average age of ER patients was 9 years old, and the most common injury experienced was an elbow fracture or knee fracture. 95 percent of the fractures happened at home, typically in someone’s backyard. “Whether it’s 80,000 or 100,000, that’s still a huge number of totally preventable injuries,” Loder told USA Today. “The way to prevent it is not to go on it at all. There are lots of other ways to get exercise.”

But others, like Mark Publicover, who invented the trampoline safety enclosure and founded the trampoline company JumpSport Inc., say that other outdoor activities — like biking, swimming, or playing on swing sets — pose an even higher risk than trampolines. “If you look at all of the high energy activities kids can play in, trampolines end up being pretty much the safest things that they can do,” Publicover told USA Today. Other parents believe it’s quite simply a matter of supervision: If you leave your trampoline in your backyard without a net or with decaying mats, and you don’t watch your kids when they’re outside, your kids will probably be at a higher risk of injuries.