Crunches and sit-ups are both popular abdominal exercises. A sit-up is a strength training exercise that strengthens the hip flexors and abdominal muscles, in addition to chest, neck, lower back, and leg muscles. A crunch, on the other hand, is often referred to as being half of a sit-up.
Its sole purpose is to strengthen the abdominal muscles. Sit-ups are strength training exercises that work on numerous muscle groups. However, unlike a sit up, in a crunch, the lower back remains on the floor.
Also, strength-building exercises such as sit-ups and push-ups will not result in the spot reduction of fat. Fat should be decreased all over the body, including the abdomen, to improve it. A sit-up works more muscles than a crunch. However, it causes stress in the lower back.