Concussions caused by series of hits not single blow

Concussions are likely caused by many hits over time and not from a single blow to the head, as commonly believed, a two-year study of high school football players has suggested.

Purdue University researchers studied football players for two seasons at Jefferson High School in Lafayette, Ind., where 21 players completed the study the first season and 24 the second season, including 16 repeating players.

Helmet-sensor impact data from each player were compared with brain-imaging scans and cognitive tests performed before, during and after each season.

"The most important implication of the new findings is the suggestion that a concussion is not just the result of a single blow, but it's really the totality of blows that took place over the season," Eric Nauman, an associate professor of mechanical engineering and an expert in central nervous system and musculoskeletal trauma, said.

"The one hit that brought on the concussion is arguably the straw that broke the camel's back," he said.

Researchers evaluated players using a type of brain imaging technology called functional magnetic resonance imaging, or fMRI, along with a computer-based neurocognitive screening test. The fMRI scans reveal which parts of the brain are most active during specific tasks.

Thomas Talavage, an expert in functional neuroimaging and co-director of the Purdue MRI Facility, said the scans indicate players are adapting their mental processes to deal with brain changes.

"The changes in brain activity we are observing suggest that a player is having to use a different strategy to perform a task, and that is likely because functional capacity is reduced," Talavage said.

"The level of change in the fMRI signal is significantly correlated to the number and distribution of hits that a player takes. Performance doesn't change, but brain activity changes, showing that certain areas are no longer being recruited to perform a task," he said.

The findings of the study are contrary to conventional thinking.

"Most clinicians would say that if you don't have any concussion symptoms you have no problems," Larry Leverenz, an expert in athletic training and a clinical professor of health and kinesiology, said.

"However, we are finding that there is actually a lot of change, even when you don't have symptoms," he said.

The research may help to determine how many blows it takes to cause impairment, which could lead to safety guidelines on limiting the number of hits a player receives per week.

"Any change in fMRI data is a concern, but we don't yet know what these changes mean, what they translate to, in terms of cognitive impairment,reedlove said.

A common assumption in sports medicine is that certain people are innately more susceptible to head injury. However, the new findings suggest the number of hits received during the course of a season is the most important factor, Talavage said.

"Over the two seasons we had six concussed players, but 17 of the players showed brain changes even though they did not have concussions," he said.

"There is good correlation with the number of hits players received, but we need more subjects," Talavage said.

The study has been published online in the Journal of Biomechanics. (ANI)