Even football players who haven't experienced a concussion need time to recover from the head impacts they receive during the football season. A study published today in PLOS ONE reveals that the six month-long no-contact period that players are given between seasons isn't giving their brains enough time to recover. Researchers say this failure to recuperate could contribute to the kind of long-term cognitive disorders that some former-NFL players have sued the league over.

between 431 and 1,850 blows to the head in a single season

To study the effect of non-concussive, repetitive head impacts, researchers put accelerometers in the helmets of 10 University of Rochester football players. The scientists used these sensors to monitor the quantity and severity of the blows that the players suffered over the course of the 2011 season. They found that each player received between 431 and 1,850 impacts to the head during the regular season. And although none of these blows resulted in a concussion, they still caused mild brain injury. Moreover, six out of the 10 players continued to exhibit these signs at the end of a six month-long resting period.

These effects are worrisome because a lack of recovery could contribute to cumulative changes in the brain's white matter, the researchers say. These changes are largely characterized by brain inflammation, and are apparent after as few as 10 high-impact, high-speed blows to the head.

The results complicate an already sensitive subject in the football community. A safer sport may require that players receive more intensive medical monitoring than they already receive. Those might be a tough sell for some teams, but one thing is clear: it doesn't take a concussion for football to endanger the brain.