Research conducted in 1990 by the NFL tells us that of retired NFL players lived with some form of permanent disability due to injuries sustained while playing football?

65%

Explanation:

American football is a physically demanding sport due the fact that  The players of NFL are required to constantly involved in a body impact with another equally strong athletes.

This strong impact often creates some sort of damage to their bones or brains.  Since NFL teams have to do a match every week , the players often have to do the matches again even before the damage that they accumulated previously haven't truly healed. This is why large portion of the players got some form of permanent disability after they retire.