Posted by: Anatomist1
A couple of people have asked for a description of a full range of motion isokinetic ab excercise. It's important to remember that, unless your abdominal musles have no muscle tone, no ab excercise is going to make your abdomen look smaller. To remove fat from your midsection, you have to remove it from your whole body, and this can only be done by burning more calories than you eat.
The abdominal wall consists of 4 layers of muscle, the fibers of which run in different directions. However, I think that three of the layers perform mostly stabilizing functions. The prime moving layer runs vertically from the ribcage to the pubic bones. This is the layer that you want to move through its full range of motion. The way to do this is by flexing, or curling your lower spine against resistance -- moving your pubis and your ribcage toward each other. Situps don't do this at all: the pubis and ribcage are in static relation while the hips flex. Crunches are best, yet most people do them in a way that fixes the position of the pelvis and only moves the ribcage. What one needs is to free up the pelvis so it can move freely and do its half of the job.
To do a proper crunch, lay on your back with your hip joint and knee joints at roughly 90 degrees each. However, instead of putting your heels on a bench and pushing down toward the floor with your heels, you need to put your feet flat against a wall or other stable vertical plane. As you curl your ribcage toward your knees, push through the bottom of your feet horizontlly into the wall and thrust with your pelvis (your butt should rise off the ground a couple inches, as should your head and upper back). Don't put your hands behind your head, pulling on your neck is only going to remove your focus from the ab muscles. Instead, palpate (lightly touch) your belly with your hands to increase focus. It takes a while to get the hang of it, but you only need to do a couple sets per session of 10 reps or so. It will become more effective as you progress, and you shouldn't need large increases in reps or sets. For a long while, the primary purpose of the exercise is to connect up the neural pathways to the muscle so that you can consciously, fully flex them. If you're doing it right, you should shake and quiver a bit at full contraction.
There it is. It's not as complicated as the description may sound, and I'm not sure anyone will be able to learn how from this. What you really need is someone to demonstrate and watch you while you do it to provide corrective feedback. If anyone has any success with it, let me know. I know it works, I just don't know if this description is adequate.