Abs tend to have a much different approach. If you are trying to build them up for core strength/health and doing weighted lifts with them, once a week like every muscle group. This will probably make your waist actually grow in size. Not like you will get a distended belly like some of the big boys, but it definitely makes for growing your waist. If your trying to just make your waist look more appealing and slender there are 2 approaches. Do nothing but a few crunches once a week and run, lift, and diet. Making your abdominal muscles show is a function of total body fat, not how large they are. Hence the enormous belly that accompanies most powerful men who are also lean. The other school says to over train them. Do a bajillion crunches a day. This will theoretically help keep a small waist as it over stresses the muscle and it never swells up to its full size potential.