The Ab 5 series is considered one of the best ab exercises of all time. It’s challenging and you can modify each exercise by not taking your legs low and/or keeping your head down.
In general, use your abdominal muscles to keep your upper body curled, to stabilize your pelvis, and to move the legs from your center. Do not take your legs any lower than you can control the movement from your abs and keep your back from coming off the mat. Your pelvis must stay stable. Once Ab 5 is completed, try to counter with extension such as swan, low cobra or swimming.