Crunches and sit-ups are different - crunches have a smaller range of motion.
Tips
usage
Distinguish from 仰卧起坐 (sit-up) - sit-ups bring the whole torso up; 卷腹 only lifts the shoulder blades by 'rolling' (卷) the abdomen. Modern fitness culture treats sit-ups as outdated and crunches as safer for the lower back.
memory
卷 ('roll up') + 腹 ('abdomen') = 'roll up the belly' - exactly what the movement is. The same 卷 appears in 春卷 (spring roll) and 卷发 (curly hair).
