Lie flat on your back and draw heels up under hips wide and out to sides like a frog. Now place hands with BarBell Plate behind the head.
Curl head down with chin to chest and shoulders rounding forward and body curling up until only small of back remains on the floor or table.
Remember, this is a roll up type of movement and not a stiff back set up.
Never do any more sets and reps on abdominal work than you would any other muscle you wish to develop.
Abdominal work does not reduce. Only nutrition and a workout with a minimum of rest between sets can reduce.