They use your body weight to strengthen and tone the core-stabilizing abdominal muscles. Situps work the rectus abdominis, transverse abdominis, and obliques in addition to your hip flexors, chest, and neck.

Will 100 sit-ups a day do anything?

Do sit-ups lead to six-packs? A sit-up is actually the least effective abs exercise you can do. Doing 100 sit-ups a day will not change your body in the slightest.

Do sit-ups flatten your stomach?

Unfortunately, doing dozens of sit-up every night isn't going to give you a flat stomach. The only way to lose fat from your belly is to lose fat from your entire body. While strengthening your abdominal muscles can be beneficial, it will not make you lose the layer of fat that covers them.