Fell very hard on my knees nearly 3 weeks ago. The bruising has gone but one kneecap still has fluid over it so it is puffy and uncomfortable. I haven't done any exercise since it happened ( apart from one swim a week ago and it hurt that evening), and I'm worried about losing what little fitness I have. It is improving very slowly but I think the sensible thing is not to try and run on it etc until it is back to normal .Any ideas for exercise I could do?