These guys speak the truth.

I haven't rode in almost a week because my knees are in ****ty shape.

Mind you I had pretty bad knees before I started riding fixed...(ACL reconstruction in right, tons of hyperextension in left)

I am riding brakeless on 48x16 and it's time to stop. I am 20 years old and I'd really like to be able to walk/ride bike when I am 60. I am planning on building up a new ride, and the gearing is coming down and the brake is going on. I have strong quads from my hockey days, but my knees are shot and riding a gear this tall is making life miserable.