I also use Speedplay pedals, the light action ones, and I've been having some pain on the outside, back part of my left knee. It almost feels just like a little soreness after a difficult ride. My husband used to use these pedals until he also developed knee pain, and I guess it was because there was too much float on the pedals, so his foot would be sliding all over the place while pedaling, so the alignment just wasn't very good. He got pedals with a float that he could adjust (since you can't adjust it on these particular pedals) and since then hasn't had a problem. Good luck. I still haven't decided what I'm going to do. Getting a fitting isn't financially in the cards for me right now.