THE MAIN MOVEMENT of the abdominal muscles is to shorten the distance between the sternum (breastbone) and the pelvis. To work the abs, do exercises that move your sternum towards your pelvis or your pelvis towards your sternum. Keep this in mind as you do the exercises. The point is prevent lifting from the neck or using other muscles.
If helps to visualize the correct movement as you do them; so, when you are working your abdominal muscles, concentrate on using them to shorten the distance between your sternum and pelvis. Imagine your abs doing this as you exercise.
Crunches vs. sit – ups
Crunches are, loosely, a type of sit up. Although there are variations, a classic sit – up is the motion in which you are on your back and you pull your upper body all the way up and all the way down for one sit – up.
Few fitness experts still promote this kind of sit – up because it can hurt your back, especially if your legs are straight. I recently had to perform this kind of sit up (bent knee , not straight) for a fitness test, so they are still around. (I was sore for days!) The words “sit – ups” and crunches are often thrown around as meaning the same thing, but basically, crunches are smaller, more subtle movement that isolate an area.
The hip flexors, or ” iliopsoas ” muscles, bring the thighs closer to the torso. Sit-ups have a bad name because they emphasize the sitting motion and use the iliopsoas instead of pulling your sternum and pelvis together.