not all knee problems are created equally. I have had two bad injuries on my right knee within a two year period. Fractured the tibial plateau both times. Lots of spraining both times. ACL is a little stretched. I can't bend it nearly as far as my good knee, it just stops.

I cycle every day, and it's pretty much the best thing for my knee. I was sick the other weekend and didn't go out for two days and that brought my limp back because my knee stiffened up.

It helps that I was quite active and athletic before the injuries, and I'm also a lightweight which is great for knee problems. And I know even I often come up with excuses because I'm terrified of reinjuring my knee in a stupid way, and the looseness in my acl makes me take great care hiking in loose terrain and I pretty much don't run anymore, though I can. But some people have enough range of motion issues for a proper pedal stroke to be an issue, or the mixture of bad knee and bad bike handling and horrible fitness makes them just focus on the "bad knee" part and give that as an excuse. I've also known people with meniscus issues and anything besides a super easy gear gave discomfort.