Control over the muscles of the side abdominal walls can be learned. This is support. Bear in mind that the cords are apart for inhalation and closed for singing. When the breath is let go, one hears a grunt. In the international professional singing world, sighing, minimal breath, or grunting maneuvers do not play an acceptable role in balanced voice production.
Air is already present in the trachea, ready for immediate use.
Enough of the negatives. Now for the positives of the appoggio maintenance. Let us now get down to the nitty-gritty of how to find the appoggio and maintain it. As ever, what should be done is the easiest to explain. How to do what should be done is much harder.