Oh, what a mess I have created! After having read the last few pages, it seems to me that there are 2 distinct problemes that are, however, related.
1. The reason so many persons have a probleme w/ core, including Ant, is that they do not know what it means. John, Peaches, and one or two others have tried, very well I might add, to explain it, but there seems to still be confusion. It appears that Ant is trying to dissect core from center from shoulder blades from chest from lower back from..... from..... from. at the risk of being oversimplistic, simply picture the body as the Eiffel Tower, think of the core as the part of the tower atop the base. The core is not either one of the afore mentioned parts; it is all of the afore mentioned parts, each with its own weight/placement/function, but each working in time with the other/s.
2. The other issue is how to do what we want to do once we identify what it is that we are trying to do it to/with. Most of you are trying to correct the core; by lifting the rib cage --A DEFINITE NO--, by stretching the sides --correct, but not alone--, by standing upright w/ good posture --whatever the hell that is. Though the latter 2 are the extra points, neither is the touchdown.
Correcting the core depends first on having a good "grounded" (remember the point of the thread?) center. To do this, we go back to the Eiffel Tower image and, after having stood erect, 'but relaxed', and forwar over the insteps of the feet, we use the aduc... nevermind, the muscles of the insides of the thighs to pull our upper thighs and knees inward. Without tension, we have created, now, not only a vertical center, but a horizontal center (very much like the tower), and we are indeed grounded. Keeping the tower part of the body pulled up and centered over the base, we begin to feel the muscles of the core coming into play to maintain this posture.
Once attained, this is a very relaxed and comfortable posture/position. Given a good embrace, there is not much else required (core wise). I know how difficult this is to explain via cyber, but I hope it helps.