Before describing this routine to you, let me give you my opinion on the abdominal muscles and how I believe they can most effectively be trained. Despite what you may have heard, the abdominal muscles are just like any other muscle. They fatigue with stress and need ample opportunity to recover. You would not do a hard chest or leg workout on two consecutive days, so why do that for abs? Another thing that people don't think about when training there abs is what exactly the exercises they are doing actually do to that muscle. There are a couple things that I mean by this. First, it is generally accepted that to gain muscle mass you want to lift heavier weights and to tone your body you want to lift lighter weights with more repetitions. Think about this principal when applied to the abdominal muscles. Do you really want to bulk your stomach? You may do a lot of heavy medicine ball exercises and have very strong abdominals, but at the same time they will probably be bulky and only somewhat toned, leaving you with somewhat of a "pot belly" appearance. Most people are trying to tone their midsection. This means only using light weights, or even just body weight, and performing a lot of repetitions when it comes to the abs. Another benefit of high repetition exercises for the abdominals is that the strength one builds is a special kind of strength known as muscular endurance. This is especially important for athletes because in many sports, the "core", or ones inner abdominal muscles, is where much of ones power, strength, speed, balance, and skill originates from. It has become well known that in order to maximize athletic ability one most develop not only a strong core, but one with good muscular endurance.
This ab routine should take anywhere from 30-45 minutes depending on how long a rest you take between each exercise. I suggest not taking longer than a minute between each exercise. Remember in addition to strengthening and toning the abs, we are attempting to build muscular endurance, so this means you cannot allow them to have too much recovery between sets. I also suggest performing the routine in the order that I have listed here. I find it is a good mixture of crunch/sit-up type exercises that work the Rectus Abdominis, core/stability type exercises to work the deep inner abdominals and lower back, and twisting type exercises to work the obliques. Keep in mind that this is a very advanced workout and you should not expect yourself to be able to do the full amount of repetitions I have listed here. Try starting with only half of the repetitions or half the workout and add more as you get stronger.