It seems that there are many more injuries in the NFL than there used to be, especially hamstring and ACL/MCL. I'm curious as to what the cause is, and it's probably a combination of the following:

1. PEDs - Overtime, PEDs tear down the body, making the players much more prone to injury

2. Lack of flexibility - Players are much more muscular than they used to be. Gym time seems to be spent building muscle and speed, much more than in the past. Things like the NFL Combine focus on numbers that don't really relate to football skills, so the players are more worried about looking like body builders than being in "football playing condition".

3. Rules to protect head injuries - If players are trying to avoiding getting penalized for hitting a player high, the alternative is to hit them in the legs.