I'm afraid you're on the wrong forum if you expect straight answers, Thelistmaker. Tai Chi people like to be En16m@†1c - clarity is beneath them. It's a lifestyle choice - an identity affectation - an off-the-shelf pose not unlike teen-angst or nihilistic horror frenzy. If left untreated it can grow into a full-blown personality disorder. The spot that is 3 finger widths below the navel is a point which is meant to be some kind of "gate" to an "energy centre" called the dantian ("elixir field"). What has this got to do with martial arts? Well for most Tai Chi people Tai Chi isn't about martial arts - boundaries blur making it a great pseudo-religious sexual lifestyle mishmash of nonsense. They find whimsical, elusive and even seedy connections where there aren't any and often back each other up in such nonsense despite everyone's nonsense being a bit different from everyone else's. The one thing they are clear on is that it is not clear or understandable to ordinary folk. Submission to a GR8 M4ST3R is the only way to be be led to a pitiful attempt at understanding. So back in the real world I guess a physical body has a centre of gravity, and you want to get it pretty low and keep it low. If someone raises your centre of gravity a.k.a. "raises your qi" they can topple you more easily. A separate issue is body mechanics. One of the Taiji classics talks about power being rooted in the feet, issued through the legs, directed by the waist / hips and and manifest in the hands. The legs push everything else into place from the ground up. Works for me. Some Taiji people prefer the idea of everything emanating outwards from their imaginary all-purpose "energy centre" (dantian) and returning to it again. A more mundane explanation is that your waist and hips is where you generate your power from (Zheng Manqing used the term "yao kua" - waist hips). As your hips open and close to allow you to turn your torso, there isn't really any conflict with the "from the ground" theory. I open my non-weighted leg from the hip (opening the hip fold), then shift all my weight onto that leg, turning the torso when the weight has passed the half-way mark and turning the other leg with it, pivoting on the heel - this closes the hip fold again. The power is generated by the legs and torso and the hip region could be said to be active throughout - inititating and finishing the movement. Some Tai Chi folk say their "energy" shoots out from their "dantian" and bounces up from the ground - which basically tallies with the above power from the feet thing, not that the "energy" people will admit it - they'll say it is all to do with "internal energies" akin to bioelectricity. Of course you could then argue that your nerves send signals out to your muscles from your spine which could tally with that idea, but of course that would be too mundane (Western) an explanation for a Tai Chi person to admit. There must be no common ground - the Ancient Chinese were completely ingenious unlike their foolish Western counterparts who achieved nothing whatsoever in the fields of science, medicine and anatomy So they'll resist all attempts at reconciliation and tell you you don't understand because you've never trained with a R34L M4ST3R even when you have but they just had a much more mundane and less esoteric understanding of everything and knew not to blur so-called "internal alchemy" with body mechanics. Of course everything other than body mechanics and center of balance is complete nonsense. Anyway, that's my contribution to this discussion.