For the majority of people, good abs are expressed in the form of a 6-pack. Ponder this clip: YouTube.
Often at the Shaolin temples, a monk puts a bowl against his abdomen, engages his abdominal muscles and will ask the largest visiting tourist to pull it off. Much to the surprise of all, the bowl sticks. While focused on trying to pull the bowl off the monk's stomach, the tourist does not realize that he is unable to move the small monk off his feet.
The monk’s abdominal training and breathing allows him to withstand the tugs, jerks, and twists of the largest force. This is core conditioning at its finest: breathing, muscle control and stance.
When working the abs, there are two positions of action: concave and convex. Most people work in the convex/“tummy out” position because it is easier. Abs in the concave/“sucked-in” position is more body defining, and involves a greater level of thought and core control to execute the same activity.
The monk’s ability to suck in his abs to hold the bowl demonstrates incredible abdominal control that allows him to deliver force into this stance.
Over a lifetime, we learn to push our abs out when standing, bending over to pick something up, and also while sitting in front of a computer. The convex/“tummy out” position has obvious effects on the body’s stature. It is only when we do extreme overhead lifting that we typically “suck in” our abdomen to stabilize the core.
As an exercise, try using the abs in the concave/sucked-in position in various activities: lifting an apple, bending over your desk, standing in line, etc. The next time you go to pick up an object, suck in your abdominals and tighten them before lifting. You might want to try it several times slowly until the work feels secure in your abdomen. This is a very intense abdominal exercise if done right. If you do not feel any different, you are not using your core. If you do access your core, you will feel a sense of control similar to the Shaolin monk.