Ditto, although for me it's usually the neck. Permanent C2 damage, nothing I can do to completely prevent the spasms. Kept me off the bike Friday and Saturday despite the relatively nice weather. Maybe Sunday. Sometimes it's bad enough I'll take a muscle relaxer, although those tend to make my legs feel like mush - I can still ride, just slowly. My concession is a comfy bike that's soft enough to soak up the bumps while still being efficient enough for 10-20 mile rides and modest hills.