just curious whether to do fast or slow sit ups..

I know I will do it more properly when doing it slowly, but I feel more stress on my abs when doing it fast(due to having to use more resistance when doing down fast)

cuz if I do it slowly, I use lesser resistance when going down as slow speed.

is sit ups the same logic with push ups? cuz with push up, I do it fast to train more power, and I do it slow to train more endurance.