Pilates class (bands) 50:00 
As a longtime member of the "it hurts to kneel club," I've learned a number of modifications to Pilates moves/exercises, and instructor Mary doesn't mind and actually always suggests modifications for most moves anyways in case there are any beginners in class. Others dealing with knee injuries or problems have looked to me to see what I do. :-)
Sometimes the modifications are harder (on other muscle groups) than the original. One exercise that the class does on hands and knees, extending a knee behind while pressing on the band, is so much harder if you try to do it standing (leaning over some to try to get the same angle) because the opposite hamstring gets worked more (than when kneeling).