Some mower manufacturers tighten the blade bolts so tight that it requires a impact wrench to loosen them, I had purchased a new Bad Boy mower year before last (Since sold it) and I wanted to install some mulcher blades and had to use a 4' cheater bar to remove the original blades, they were way over the torque specs given. I usually use never seize on the blade bolts (I know some folks disagree but I've never had a problem with them getting loose) when torqued correctly.
Curt
Curt