L4-L5 and L5-S1 are my worst. My back was at its worst 12 years ago, but has slowly gotten better the last few years. I've stayed with the core muscle exercises, made sure to keep my weight from getting too high, and tried to be more careful to lift correctly, and not overdo it with the lifting (not easy to do if you work in machine shop maintenance).

And I ride recumbents. They're pretty much like therapy for my back.