i'll ask one of my bosses on Monday and see what he says, he's a triathaloner. my experience is in hiking, so take it for what it's worth.....the tendons is what I was thinking along with your doctor. the patela tendon that holds the kneecap in place, when the muscles in the legs are getting overworked, it has less strength to hold the kneecap solidly in place, it starts sliding just slightly and that causes a slight but not severe knee pain. you can buy patella braces for the knee, but to start with, just to see if this might indeed be the case, tie something like a bandana medium tightness just underneath the kneecap. hopefully that might work for you. I agree with the above posters that I don't think it's the shoe. i've developed bursitis in my knee from new insoles in my shoes (the slight change in pronation caused it), but since your shoes are worn in already, they're probably not the source of the problem.