I've been running for a couple of years but have always suffered from a painful LEFT knee. Until today I had never seen a doctor or a consultant to find the cause, I've always relied on a knee support and a few neurofen to get me through, not ideal. I went to see a physio today and after being pulled around like a 70's Stretch Armstrong I was told the cause was due to tight muscles around my RIGHT hip and RIGHT lower back which in turn was affecting my LEFT knee, odd I know. She told me it was easy to cure and showed me a few simple excercises to perform. Hopefully they will do the trick. I've searched this site and have read many threads concerning knee pain coming to the conclusion it can be caused by a number of things. Moral of the tale? best get it checked out.