While the Rectus abdominis is colloquially known by many as the "six pack," some people may display four "rows" of abs, giving them an eight pack, while others (most notably Arnold Schwarzenegger) show just a four pack. Rather than indicate anatomical variations in the actual abdominis muscles, the number of packs a person displayed is determined by the number of bands of fascia (a kind of connective tissue) crossing the abdominal region.
Think of rubber bands stretched around a balloon. The bulges in the balloon represent the parts of the Rectus abnominis that we see. Just as strips of the balloon are pulled in and obscured by the bands, so too are strips of our abdominals pulled covered by fascia. So, no matter how many sets of crunches or leg raises you ever do, the number of rows of "abs" you have now will never change.
Think of rubber bands stretched around a balloon. The bulges in the balloon represent the parts of the Rectus abnominis that we see. Just as strips of the balloon are pulled in and obscured by the bands, so too are strips of our abdominals pulled covered by fascia. So, no matter how many sets of crunches or leg raises you ever do, the number of rows of "abs" you have now will never change.