I have horrible knees, they like to give out when i am walking and swell up to about 2 times thier normal size and i cant walk dor at least a day. I have started doing pilates its all on your back or sitting and it is really a work out. you might also want to try yoga it is slow and no bouncing around and i have done it many time and only had my knee give out once on me. and trust me even though it does not look like a work out you WILL feel it the next day.