>>76408162 (OP)I usually do decline situps at -20 degrees while holding a 20 kgs medicine ball. The number of sets of this usually equals the number of chest sets (6-6), but sometimes I just can't be assed to do so much of these, so I do half (6-3).
Sometimes I also can't be assed to do these, and when that happens, I opt for an ab crunch machine instead. But as that machine is pretty uncomfy on the lower back, I prefer to just do decline weighted situps.