Thanks for the reply!

I have not had an injury to the knee since the patella tendonitis problem, which seemed to have cleared up several months previously.

I do stretch my quads etc. before and after each ride, these do feel fairly tight but no real pain.

While cycling the pain only seems to return when I ease up going downhill after a climb. But I can cycle happily (once warmed up) uphill for an hour or so without pain.

Thanks