A routine hit to the head during a high school football or hockey game may result in subtle injury even if there is no concussion, U.S. researchers say.Lead author Dr. Jeffrey Bazarian, associate professor of Emergency Medicine at the University of Rochester Medical Center, said the study involved a small sample of athletes -- nine athletes and six people in a control group -- but it raises powerful questions about the consequences of the mildest head injury among youths with developing brains.Bazarian and colleagues Tong Zhu and Jianhui Zhong used wild bootstrap -- a new statistical approach -- to analyze before-and-after images of the players\' brains from diffusion tensor imaging -- a scan similar to magnetic resonance imaging, but it does not relay pictures, rather it captures and relays quantitative data that must be decoded and interpreted.The study, published in the journal Magnetic Resonance Imaging, found among the nine athletes, only one was diagnosed with a sports-related concussion during the 2006-2007 sports season.However, six others sustained many sub-concussive blows and showed abnormalities on their post-season diffusion tensor imaging scans that were closer to the concussed brain than to the normal brains in the control group, the study said.\"Although this was a very small study, if confirmed it could have broad implications for youth sports,\" Bazarian said in a statement.