“The main difference between the two is that unlike a sit-up, in a crunch, the lower back never leaves the floor,” explains Katharine Glazer, CPT. Basically, a crunch is a more targeted and isolated ...

A sit-up, on the other hand, has a larger range of motion and targets multiple muscle groups at the same time—rectus abdominis, hip flexors, transverse abdominis (deep core muscles), obliques (side ...