CHICAGO (AP) — Playground concussions are on the rise, and monkey bars and swings are most often involved.

That’s according to a new study from the federal Centers for Disease Control and Prevention. Researchers there examined national data from 2001 through 2013 on playground injuries to kids aged 14 and younger who received emergency-room treatment. Of almost 215,000 kids on average treated yearly, almost 10 percent had traumatic brain injuries including concussions.

Most injuries were mild, but all concussions are potentially serious and the researchers say the trend shows kids’ concussions don’t only happen in sports.

The study was published online Monday in Pediatrics.