yoga. no kidding. I had chronic probs with a muscle near the top of my spine (causing blinding headaches and neck pain/stiffness) and the daily cycle commute gave me no chance to rest it. also suffered sciatica since breaking my leg (esp when fatigued). yoga fixed my muscle issue and while I was doing the yoga my back was loose all the time and I felt much more energised just for that reason.
I found out that with some of these muscle problems, the issue is that while the muscle is in pain it won’t relax; unfortunately, all it needs is to relax (perhaps for several separate periods) for the pain to go away. YMMV of course.