1-2 days a week, and HEAVY. Ditch the sissy high rep LOW intensity stuff and do HEAVY sets of ten weighted situps, lat-pulley crunches, hanging leg raises, and even some of the better leveraged ab machines. Forget the traditional bodybuilding dogma that you must isolate the abs from the hip flexors. They work together when doing the big lifts like squats and deads were you need them most, so they shoukld be worked together when doing ab work.
Iron Addict