When I was around 10 years old I had knee surgery for discoid meniscus. My knee cap would dislocate and lock up. It was removed. I have continued to have popping in my knee. I recently started (about 6 mos.) going to the gym. I started to run on the treadmill and take an abs and total body class. I think I remember that I am supposed to build up the muscle above my knee before I run on the treadmill. So I have several questions- Is this true? running on the treadmill doesn't really hurt my knee (sometimes it aches but it does that when it rains so I'm not too concerned)- use of the bike makes my knee sting, is there something else I can/should use? I tried the elliptical and that hurts as well. Is there anywhere I can find information on what I should be doing? I feel awkward and uncomfortable in the classes and am wondering if this is just psychological- the trainer tells me that I am doing the execises correctly.