The classic crunch works the rectus abdominis, which is why most people focus on that move — for that “six-pack” look. The problem is, a crunch-only routine isn’t doing much for strengthening your core — or the rest of your body for that matter. “You need to have variety,” says Holly Rilinger, Nike master trainer.
To vary your workout and let those other ab muscles come out to play, Rilinger recommends including exercises such as planks, squats, and lunges. “[These] also require you to engage your abs and your core … and actually give you more bang for your buck,” says Rilinger.
Britannica. (n.d.). Abdominal muscle.