"Tough As Nails": runners knee

I often get pain in one of my knees and so recently visited a physio. he explained that there could be many causes, but most likely, in my case, the knee joints are slightly out of line, meaning joints and cartilage rub and cause pain. this could be from either over or under pronating. he recommended some quad exercises for me to strengthen certain muscles to help bring the knee and surrounding muscles back in line. I recommend you see someone about it though. You don't want to do any serious injuries to yourself! And it could be a simple prob.