When I was growing up, my father had an electric back massager called the “Jeanie Rub.” He’d gotten it soon after he’d been in a car accident and hurt his back. The engine on this thing was so powerful and rough that it was like getting a massage from a jackhammer! You even had to hold it with two hands or you'd lose control of the thing. Your entire body would shake like the thing was trying to tear you to bits. I’d be flexing my muscles so hard to withstand the torture that I’d end up more tense than when I started.
Needless to say, it was not a relaxing experience. In fact, my father was the only one that could stand it. But it was the only massager in the house. So, if your back hurt, it was damned if you do, damned if you don’t. Pick your poison and hope you survive.