Young athletes with loose helmets had the highest rates of concussion symptoms, such as drowsiness, hyper-excitability and sensitivity to noise. Their concussions also lasted longer and were more severe, the study found.

"Concussions are very complicated injuries, but [loose helmets] could be one more risk factor for experiencing more severe concussions," said study author Dr. Barry Boden. He's a sports medicine specialist at The Orthopaedic Center in Rockville, Md.  Read More