Don't know, just happens. Especially since I'm over 30. I lift something in the worst possible position, because I'm distracted, and suddenly I pulled my back

Don't know, just happens. Especially since I'm over 30. I lift something in the worst possible position, because I'm distracted, and suddenly I pulled my back, or whatever. Grabbing something, turning around, remembering I need something else, just rotating my upper body and grabbing it, done. Lifting a big mirror, without bracing myself. Etc.