The abdominals are unlike every other body part. With muscle groups such as chest, back, or shoulders, you make the best gains from a series of heavy sets. You lift as much weight as you can for 6, 8 or 10 repetitions, and you only complete a total of 8 to 20 sets per muscle group. The abdominals are very much different. You see much better results from abdominal training when you train them more frequently, with little to no weight, and much higher repetitions.