So am I right in assuming that the way to do cruntches at 50% of your max so forth and so on would be lengthening the time it takes you to relax to the laying position again?

sorta like this

1st set 12 held for 1 second then drop..
2nd set 10 held for 2 seconds then drop (slowly of course)

so forth and so on...

Toph,

That's how I do them. I also really focus on using the abs to do the lifting and try not to use shoulders or back at all. Sometimes, if I feel I'm not hitting the number I'm aiming for, I'll just contract my abs at the top of the crunch and hold it for as long as I can and then go back down.

I'm sure you can think of ways to make yourself suffer...

Ciao, Dig

I never really thought of doing it that way , I just doubled the number of reps , I will have to try that way .

I use an ab weight machine at the gym. Boy, does it burn!

You aint kidding skamito I did them with 80# today and boy I could feel the burn. I also hold at the top of the contraction and pulse. Talk about agony.
Laurie