When things got bad for me before I was diagnosed, one of my most disabling problems was severe back muscle spasms. no amount of muscle relaxants would deal with it. They didn't go away until I started regular anti-inflammatory treatment (at the time it was NSAIDs). I would have said my muscle spasms were definitely part of the disease, caused by uncontrolled inflammation near the muscle insertions. I get what you say about exercise making it worse. When the muscles are going into spasm its really hard to do any kind of movement without it grabbing you. I can't take NSAIDs any more, and I'm not eligible for anti-tnf treatment here, so if I feel my back going like that again, I deal with it with a short course of pred.