A new joint study by the US Department of Veterans Affairs and Boston University found that 87 out of 91 former NFL players who donated their brains for examination showed signs of chronic traumatic encephalopathy, the degenerative brain disease also known as CTE. The report out of the nation's largest brain bank, which received a $1 million research grant from the NFL in 2010, supports prior research suggesting that playing football could have long-lasting neurological effects over the course of an athlete's life.

As reported first by Frontline:

In total, the [Boston University] lab has found CTE in the brain tissue in 131 out of 165 individuals who, before their deaths, played football either professionally, semi-professionally, in college or in high school.

Forty percent of those who tested positive were the offensive and defensive linemen who come into contact with one another on every play of a game, according to numbers shared by the brain bank with FRONTLINE. That finding supports past research suggesting that it's the repeat, more minor head trauma that occurs regularly in football that may pose the greatest risk to players, as opposed to just the sometimes violent collisions that cause concussions.