I have never had a back problem. I use it to rattle my equilibrium a bit, thus strengthening it. I only go for about 5 minutes at a time. I feel the veins in my head enlarging. What a head rush!!!
That's another good part, it improves circulation, they also claim though I haven't tried it yet, that if you read inverted you can retain an extra 15% of what you read.
I had a bad herniated disc which has caused me much pain and discomfort. I think I have tried all known treatments including acupuncture. As NAS did I bought a Teeter inversion table and I agree with him it is well worth the money and has many side benefits but it did and has helped me with my back problems.