There was no careful screening of any kind when I went for the free session. I emphasized that I was 8 months post op total knee replacement and was concerned about the machines doing harm and I was assured it would not be a problem. I knew immediately after the session that I hurt the knee and I'm lucky in that the hardware that was put in my knee is good but the likelihood is that I tore muscles and ligaments because the knee was not totally healed yet. I can see why they insist you sign a waiver of liability before even trying their machines. I would not recommend them to anyone after my experience. And the cost of it is ridiculous....$207.00 for a 10 minute weekly session. I want to add that 2 ½ months after Osteostrong, my knee still is bothering me.