First here are my stats:
6'1"
squats: 345x5
deads: 445x5
bench: 235x5
I almost never do abs. maybe once a week decline situps to failure at 3 sets if I am motivated enough. A few days ago I joined a new gym because my Golds closed down. They got this ab crunch machine that rocks. I did three sets not even to failure and my lower abs started jerking around all crazy like and tried to freeze up on me. I couldn't bend over or it would happen. It felt like there was a creature in my stomach or something, i mean the amount of convulsing was insane I thought I was seriously injured or something, it scared the crap out of me, I mean I could HEAR the movement lol. Anyways, wtf is that crap and how can I avoid it, any ideas? I try to bend backwards to stretch them but jesus. I may do one set a day and see if my abs need to get used to this but I have abs already from squats and everything else. So bizarre.