My chiropractor told me that good abdominal muscles really help the lower back. He also said to stretch the back thigh muscles regularly(is that the hamstring? I can never remember.). According to him, those two things are very much responsible for lots of folks lower back pain and spasms. When these two things are not in good condition, the lower back must constantly compensate, thus causing it to over work and become stiff, painful, and & even to spasm.
Now that I'm writing all of this, I think I need to go do some crunches and stretching...