Just like a sponge that's squeezed too tightly, when your back muscles are tight and stiff, nothing's moving in or out.
You need to keep your body flexible and moving and keep your blood flowing. This is a way to combat that stiff, achy back by giving it a little stretch and release, the same way you'd give a sponge a little squeeze and release.
This stretch is called a barrel stretch but I think of it as if I'm holding a beach ball.
You're going to round your body around the beach ball and pretend like you're trying to set it down beside your foot while you round your spine forward. I don't care how far you go or how close you get to the floor, just lean in that direction.
You're going to feel a stretch across the side of your back. Stay there for just a couple of seconds, then go around to the other side. Just five times to each side or you can go up to 10 times, whatever feels good.