Those who are familiar with the classic ten tai-chi essentials should have heard of, and perhaps are practicing, the requirement of灵虚顶劲 (Head with chi). Relevant to the subject of discussion here is the visualization that one's head is being hung through one's hairs (顶头悬). This visualization can assist a practitioner's spinal cord to be gently stretched upwards (incidentally the gist of zhan zhuang, as relevant to the discussion here, is an yin/yang interplay between the gravitational force, which acts on collapsing a relaxed body, and one's chi force working against the gravitational force, which acts on stretching the same body through stretched points in the fringe, like the finger tips and...a hanging head, among other things).
In addition to stretching the spinal cord open, another important target is to stretch the pelvic joints open. And to achieve this objective, a practitioner can best make use of a balloon visualization of an activated belt channel.
Question 1: What do you mean by an activated belt channel? If one can mindfully circulate one's chi around one's belt channel, one's chi belt is activated.
Question 2: Where is the relevant position of the belt channel? For the purpose of this visualization, the belt channel should be at the level of one's diaphragm.
Question 3: How to visualize? Visualize a number of balloons being tied to one's belt channels with the result that the balloons lifting up the belt channel which in its turn lifting up or opening one's pelvic joints.
As I noticed in the literature, balloon visualization, minus chi-activated belt channel, is not uncommon in the practice of Pilates. Pilates is a form of mind-body exercise not without a reason!