Left field idea - may be unrelated but perhaps worth considering?
Look into diaphragmatic breathing.
Many people, and I'm one, have a tendency to exhaust the secondary breathing muscles - scalenes, traps, etc because they employ collapsed or chest breathing. Diaphragmatic breathing take a conscious effort to re learn but can lead to some lessening of muscle tension - particularly in the upper back.

Dx Oct 2006 B27+ undifferentiated spondlyarthropathy (uSpA) with mild sebhorrhoeic dermatitis and mild Inflammatory Bowel Disease (IBD) controlled by NSD since 2007.