I believe abs are mainly genetics. I have tem since I remeber to exist. Even when I am 16%bf I can see them.

I work them out 3x a week in the following split.

Monday:
Upper abs: 3x15/ Lower abs: 3x15

Wednesday:
Obliques: 3x15/ Lower abs: 3x15

Friday:
Upper abs: 3x15/ Obliques: 3x15

Always high resistance.