my knees used to hurt, i just rode through it and i havnt had any problem since
i was pushing a 79inch gear at the start thought, i then lowered it to 76
now i have a the 76 inch on one bike and a 72 inch on anotherbike
thowing yourself in the deep-end with a huge gear (and a brake maybe?) and then lowering the gear as time goes on is one way of doing it i suppose