I did a dumb thing in my mid-40's--I was substituting for my youngest son on his paper route, and I tried carrying all the Sunday papers at one time. Not smart--when I woke up the next morning I couldn't move!

I was prescribed a number of stretches and also abdominal strengthening exercises. Any time I skip them, my back starts hurting again! Your lower back is supported by your "core" body muscles, particularly those of your abdomen, so anything that strengthens these is good. Even exercise walking with trekking poles (aka Nordic walking) helps--it turns walking into a full body exercise.