If there's one thing that a majority of Americans hold near and dear to their hearts, it's American football. Some athletes start playing this violent, hard-hitting, extremely competitive sport at a very young age, as young as five years old even. And can continue playing well into their 30s. That's 25 years-in some cases-of severe wear and tear on the body. Protective pads, helmets, and a strict set of rules are in place, but those only mitigate the risk.

Injuries, such as pulled muscles, strained or torn tendons and ligaments, and concussions are all thought to be just part of the game. Some athletes have been permanently disabled or even paralyzed due to the sport's physicality. While instances of paralysis are somewhat rare, the hard hits and the resulting bodily harm are not.

Researchers now have evidence to support the theory that even minor head bumps, over the course of roughly 20 games per year and countless practices, can result in abnormal brain tissue in players.

During a span of 3 seasons, researchers from the University of Rochester in New York studied a group of 38 college-level football players in order to determine the effects of the sport on the brain. The players were fitted with accelerometers in their helmets to record all the forces at play during season games and practices. The participants also underwent brain scans prior to, and after each season.

Using fractional anisotropy researchers were able to estimate just how well white matter brain tissue can carry neural signals, a key aspect of a healthy brain. The players accumulated some19,128 hits collectively. And by the time their season was finished, the players on average had lower measures of fractional anisotropy in their right midbrains-a part of the brain stem.

The study also suggests that the reduction of fractional anisotropy is more evident when linked to hits in which the player's head was twisted, rather than hits that were direct. Those neck wrenching hits might be even more damaging to brain tissue, a result that coincides with the findings of previous studies, according to the researchers.

It is still not clear as to whether these hits cause any changes in mental performance or whether or not they are permanent. However, the study does suggest that its not only the big, crushing hits to the head that players, trainers and medical personnel should be concerned with, but also the smaller, less spectacular hits as well.