I use to swim competitevly from 13-21 and worked out 5 hrs. a day. My left knee is shot. The muscle going down the inside of my kneecap became over developed and chipped of cartlidge on my patella, causing it to loose its shape and flatten out. I have had 5 surgeries to try to correct the problem. Now I am looking at having to have my patella resurfaced, this is just after going thru a fulkerson osteotomy in sept. 02. Please whatever you do do not swim as much as I did. Ellen