i've done those both with dumbbells and also with a rope and cable. i like the cable exercise better because the resistance stays constant. see how they lose the contraction at the top and smack their knees? that doesn't happen with a cable crunch...
~KITTY

I was really hoping he'd lose his grip on that 40lb dumbell and drop them shits right on the beanbag. He'll really be able to feel the burn. Cosigns with da Kitty *meow* cable gives better consistency

try it with a band