It’s quite simple, really. Your back hurts. You’ve got a knot somewhere and you can’t reach it. You live alone. You’re too proud to ask for a back rub. You’re too poor to go get one yourself. So you figure out a way.
That way, for me, is to use a tennis ball.
You lie on the ground and roll around with a tennis ball beneath you. Find the spot it hurts the most, hold until you can’t stand it, then release and move on.
I used it constantly on my feet for my plantar fasciitis. And it works like a charm on all sorts of tight muscles.
I’d pretend I’m the first one to come up with this idea but there are hundreds for pictures that come up with you google “tennis ball massage”… so I’m just another of the believers.