Spasms, not a good sign...
spasms usually indicate overwork/training or that something could be wrong with your back, more specifically your spine, like it was my case. I had a pinched nerve in my lower back that caused one side of my back to work more than the other, usually feels like a burning, tightness sensation, and you could feel knots on it as well. My advice is to take a break for a few days to see (do NOT forget to stretch a LOT too, pelvis, back, legs, etc, etc, etc, VERY IMPORTANT) if subsides. If not, or if it does but comes back, your best bet would be to visit a GOOD SPORT oriented Chiropractor for a thorough check up. You might need to get adjusted.
Corsaire Borading party....AWAY!