More than a quarter of all helmets worn by hockey players, from the NHL to youth leagues, are unsafe, according to a study provided to "Outside the Lines" that ranked hockey helmets based on their ability to reduce concussion risk.

Out of 32 helmets in the marketplace that were tested by researchers at Virginia Polytechnic Institute and State U., nine failed to earn a single star on a five-star scale and were classified as "not recommended." Just one helmet, made by Warrior Sports, received three stars. The rest received one or two stars.

A study to be released Monday will show that out of 32 hockey helmets in the marketplace, nine failed to earn a single star on a five-star scale and were classified as "not recommended" for use. Just one helmet received three stars; the rest received one or two.

"In general, they're low performers," said Stefan Duma, the head of Virginia Tech's department of biomedical engineering and mechanics.