Nice to know, thanks.
I used to squeeze at the contraction but scared myself off after reading about too many people saying it's a knee killer...not to mention everyone hating on the leg extension to begin with! My old man had knee trouble so I don't want to end up down the same path but love the leg extension for hitting quads so can't give them away completely.
Nothing else I do seems to work them as well...now I generally start with leg extensions to activate and pre fatigue the quads before squats, leg press etc, it's been working well I think. I may revisit the paused contraction as it works a treat but perhaps not at full knee lockout?