I had my right knee replaced 5 weeks ago. I can ride on the trainer at home and the spin bike at Physical therapy class. All that the PT people say I should put in is 10-15 minutes 3 times a day, along with all the other strength exercises they give me. My surgeon says to not get back on the street until after 9-10 weeks. He is a bit of a tri-geek so I trust him. Work on the bending and the straightening as much as you can and all will be well. Ride on. Plus my leg is now 10mm longer than it was. Will need to check my seat and cleat positions.