you don't need to train abs to get a six pack for example .... abs get the toned look when your body fat percentage is low.... , strong abs will make you perform better in squats and major lifts that requires stability and balance...but it's not really important to train them at all for any other reason...train them once every week with low volume that's more than enough, do for example 2 sets of cable crunches then follow them with a set or two of regular crunches or any variation of situps/crunches ...but don't waste your time doing hundreds of situps and crunches ....