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.
Yoga +1 here.
Lie on front, Stretch yourself lengthways then lift opposite arms and legs ie right arm left leg, six inches off floor. Say six sets of six.
Then get onto hands and knees and ‘the cat’ (look it up).
Worked for me after laying a patio, and do it regularly as a top up.