A new Michigan Survey Research Center study found that about one in five Canadian adolescent athletes has suffered at least one concussion.

Neuropsychologist Gad Klein says parents shouldn't be alarmed by a single concussion, and although he says the numbers look accurate, he raised concerns with the study.

"It's possible they may be recognizing symptoms that weren't really concussions," he says. 

The study, on children in grades 8, 9, 10 and 12, also relied on self-reported concussions.

It found that they show up at a high rate in teens who are active in contact sports.

Katie Travers, of Rockville Centre, says she was just 12 when she sustained her first and second concussions. The first time, she bumped her head on a dance floor. The second time, she got hit in the face with a basketball.

"I was sensitive to light -- the apple on the Apple computer -- I couldn't even be in the same room as it," she says. "I  couldn't read, and then I kept missing school, and the work was piling up."

Her mother, Nancy Travers, says she sought early treatment so that she could get back to playing sports.