Cindy, for years I had been taking gelatin (fish) for my knees and it helped. I ran out of it and didn't bother to get more. But after a while my knees started "whispering" again. And that is when you wrote about rebounding. I had told you that I was doing "heel drops" instead of rebounding, but also some bouncing on a yoga ball. By now I can happily report that these random heel drops/bouncing seem to have kept my knees totally calm. Thank you!