Advanced crunches, according to fitness expert Kiran Shawney, are more challenging and help tone the abdominal area better. To do advanced crunches, lie on a flat surface and lift the legs straight up. Ensure that your back does not form an arch while lifting the legs up and that the distance between your chin and neck are equal throughout the exercise. You can either keep your hands on either sides of the forehead or lift your hands straight up and touch the knees while lifting your chest up and bringing it closer to the legs. Push and pull your chest 20-30 times to do the advanced crunches.