where does this 'extensions damage your knees' shite come from
you get knee surgery and guess the exercise the physio will give u to strengthen............ leg extensions!!!
you should never work thru sharp pain in joints, its bad news..... back off try somthing different, ice it everynight to take away inflamation ....
what id do is start your leg workouts with calves and hams then quads,,,, your knees will be loosened up, start your quad work with high rep, slow, squeezy leg extensions, leg press , then another type of machine squat ( v squat, horizontal hacks, front squat machine etc )
ive never seen a gym with one of those nautilus machines in my life!