I'm glad to see people trying some more variation on the "ab" training other than the usual leg raise and situp or cable pulldown combo. BTW, I notice you are doing DB side bends. May I suggest you try overhead DB side bends instead. What they will do is increase the lever length so that a little weight is magnified by a whole bunch. Plus increasing the stimulus to the whole region in general by engaging the stabilization component, etc. This will keep you from ending up with 120 pound db's in each hand and wondering why it ain't enough