Like situps, crunches help you build muscle . But unlike situps, they work only the abdominal muscles. This intense muscle isolation makes them a popular exercise for people trying to get six-pack abs. This also makes them ideal for strengthening your core, which includes your lower back muscles and obliques.
Read moreWhat is a open knee crunch?
Keeping feet together, open your knees to a 45-degree angle. Squeeze your abs and lift your hips off the floor and roll them towards your chest. Pause and slowly lowering your hips back to the starting position.
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