Hello Toril, I swore not to come on here again...but I wanted to send you my very best wishes for your knee replacement. I had mine done 6 months ago. A couple of points.... do keep up with the exercises, I did but know of someone who did not and their knee never healed properly. Secondly, I would advise you to stay away from the Bodyblade for several more weeks. I investigated how the muscles are activated, and in a standing position you will be probably activating the thigh muscles, which end in the knee. Up to you, but I wasn't going to risk vibrating my replacement dozens of times a minute! I worked out it was probably all right to do it sitting down so the contractions don't travel down that far. My suggestion, since there was not any advice on QVC the last time I looked, is that you only use the Bodyblade sitting down, you can get a good arm workout, but do not use it in a standing position for some weeks yet.