Representatives who are against the daily abdominal training
People who are against a daily abdominal training, are of the opinion that the abdominal muscles are to be treated the same as all the other muscles and these can also be overtrained. Every muscle needs sufficient time to regenerate, that is 24 (or more) hours rest between abdominal muscle training.
Representatives from the daily abdominal training
Others say that the abdominal muscles are unique in that we take almost every movement a little. It requires a lot of training to bring the abdominal muscles to really tired. Therefore require the abdominal muscles daily exercise for optimal results. Moreover, many bodybuilders train their abs daily.
The golden rule
We recommend the middle way of two training approaches to choose. Parts of the abdominal muscles in three parts (lower abs, upper abs, obliques) and train each on a day specifically a part. (So übrigends also coached Greg Plitt his abs.) Thus the muscles can regenerate enough despite daily training.
Of course you have to figure out for yourself what kind of training is best for you. It is important that you should train a muscle, of which you still had soreness from the last training day.
The training is secondary for a six pack
A third opinion regarding the abdominal muscles is that the visibility of the abdominal muscles can not be improved with crunches or other fitness equipment. As long as a layer of fat (even if she is so thin), has your six-pack will always remain hidden. The decisive factor is therefore not the training but proper nutrition.