Yoga for Riders?

[wordstoasong]

First, I don't think there is a tag for this, so I tried my best. =]

Does anyone do any certian exercise/stretches for riding? I have arthrits in my knees (which my doctors say is an odd case for someone my age, 19)and they are painful at times. Today, I will be going to see a sports doctor, to see what type of stretches would be good for my sport (riding) and anything else about my knees.

Thanks everyone. =]