Rock climbing is growing in the U.S., with an estimated 9 million people enjoying the activity every year. But the side effect was detailed in a study published in the American Journal of Preventive Medicine, which found that between 1990 and 2007, the number of injuries related to rock climbing grew by 63 percent, measured by emergency room visits.

More than 40,000 people went to the emergency room for injuries caused by rock climbing in the period, with the most common problems being fractures, which made up 29 percent of the total, and sprains and strains, also with 29 percent. The study found that most injuries, 46 percent, affected the lower extremities, especially the ankle (19 percent). The average age of those in the study was 26, though there were climbers as young as 2 and as old as 74. Most injuries, 56 percent, happened to those between 20 and 39, with another 30 percent occurring in people 19 and under. A higher proportion of women were injured than in previous studies; here, they made up 28 percent of those treated.

More than 75 percent of the injuries were caused by falls, and as one may guess, the farther the fall, the worse the injury. Those who fell from a height of over 20 feet were 10 times more likely to be hospitalized than those who fell less than that, and made up 70 percent of those hospitalized for their climbing injuries.

The study was conducted by the U.S. Center for Injury Research and Policy, part of the Research Institute of the Nationwide Children’s Hospital, using data from the National Electronic Surveillance System, a program of the Consumer Product Safety Commission.