There are two guys at the gym who train abs every single day, they asked me the other day how often I trained abs, I do them once a week per trainer, she did tell me that I can add one more day if I want too. Abdominals are muscles just like the rest of your body and they do need to recover as well. She pointed this out to me, as I used to do them more. Abdominals are also involved in many other exercises. I'm sure we have all seen people pinch their belly fat and ask how many sit ups do I need to do to get rid of this. Main problem is the fat and all the crunches in the world won't help. Good old fashioned diet, exercise and CARDIO yikes!!!