Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Caution!!! May cause injury.

I was happily using this product on a daily basis for about three months and noticed that I started getting a pain in the middle of my back. After consulting my chiropractor, he told me that I had pushed one of my thoracic vertebra out of position. It has actualy been pushed inward. Now I have to kick my feet over my head daily to try to move it back into position. I have a smaller frame than most and for me, this piece of equipment hits right in the middle of my back. It would be nice if this product had a smaller size to just do the lower lumbar region. So although it feels great to use this product, only use it on your lower back and use it with extreme caution.