According to my way of thinking, the aim of creating strong abdominals, or a “honey bee” waist, (a phrase used in Switzerland), by a forced “pulling in” is self-defeating. Holding in the stomach reduces the amount of motion available to the diaphragm. The organs receive less of a massaging effect since their motion within the abdominal cavity is restricted; in turn reducing their tone and making the stomach bulge even more. Pulling in the abdomen causes the ribs to lift and buttocks to tuck.
I remember being given these instructions “suck in your stomach, it will keep the weight out of your legs and make you become lighter”. Without fail this caused me to become very tense and rigid, I could not breathe properly and under these circumstances centered, fluid movement seemed minimal. From a standpoint of physics, the only way to become lighter is to lose mass or move to a planet with less gravitational pull.
The aim is to achieve vitality rather than a tight feeling in the stomach area. If you join with gravity you will be much more successful in the end. You need to use the ground under your feet efficiently and up through your bones. Once the gripping body is freed, the muscles will align and lift. When you can feel your weight you gain control and find stability. To be lighter you need to feel your weight.
There is no better training for the abdomen and the organs than deep breathing. I should mention here, that in many cases nutritional factors play a role in abdominal imbalances. On exhalation the abdominals naturally organize the organs toward the center of the body. Exercising the muscles of pelvic floor will create deep support of the abdominals and balance of the entire spine.
How to find your pelvic floor:
Sit up straight on a wooden stool (no pad), feet & knees a few inches apart. You should be able to feel two egg like bones (if not gently rock back and forth and you will feel them). These are your sitz bones close your eyes and find your breath moving inside ribs opening and closing chest rising and falling (not forced breathing). Bring your attention to your sitz bones and on inhale see if you can feel them move away from each other and on exhale towards each other. (This is a very subtle movement) Once you can sense this feeling in your body you are connecting with your pelvic floor.