You can be sitting on a bench in the of some not feel any tenseness.
A massage therapist can massage the muscles and joints that will be affected by your arthritis. You don't need steel solid abs, but the better you are conditioned the better overall back support you will get. https://Medium.com/@muscleandjointcare/thailands-best-kept-secret-for-muscle-and-joint-health-13514aa92e07