Full range, full send. The classic ab builder.
Roll up vertebra by vertebra. Don't yank your neck or fling yourself up with momentum.
The sit-up takes the trunk through the biggest flexion range of any floor ab move, the abs curling the spine off the floor before carrying you all the way up to vertical. That long range and easy loading progression are why it has survived every fitness trend since forever. The full movement asks more of the core than a crunch, and rewards it with more strength through more range.
Crunches isolate the abs through a short range, sit-ups train the whole trunk through a long one. If your form is clean, the sit-up gives you more range and more challenge per rep, crunches are the fallback when you want strict, short-range burn.
Either works, as the setup allows. Anchored feet let you do more reps and go harder, unanchored keeps more of the work in the abs. A smart split is unanchored sets first, anchored sets when you fatigue.
Stop pulling yourself up by your head. Rest the hands lightly wherever you hold them, keep a fist of space under your chin, and let the movement start from the ribs curling down, not the chin jabbing forward.
