Why is it that some tai chi (taiji) teachers love to mystify their subject? There they stand in front of a roomful of eager souls, hanging on their every word, and what do they do? Instead of maintaining a helpful balance of theory and practice by providing a solid and expanding experiential basis for every principle taught, which would normally dictate that they talk a lot less and encourage more actual practice, they start waxing lyrical about things like how the root goes from the sole of the foot deep down into the ground.
Ah-huh? One of my teachers put an interesting twist on rootedness by asserting that the strength of a practitioner's root is actually a measure of how far the ground has travelled up the leg toward the centre or tantien.
Perhaps he had been influenced by that great Irish comic novel The Third Policeman by Flann O'brien, in which he presents De Selby's inter-mingling atomic theory where a man who rides a bicycle over a bumpy road every day takes on bicycle-like characteristics, leaning against the wall or standing with one foot propped on the kerb, while his bike begins to show signs of humanity - moving closer to the stove at night, tell-tale crumbs around the front wheel etc.
I've always remembered that particular tai chi session.
Afterwards while we were all sitting down the teacher went around pointing out how far up the leg of each student the root had travelled.
This he could see with his superior vision, we were given to understand.
This little piece of theatre rather spoiled what for me had been a useful pointer to developing my practice, as I knew full well that he was now taking the opportunity to map out the pecking order in the class along the lines of his own favoritism (I shan't go into the question of how I knew this - write and ask me if you're really interested to know).
But from a didactic point of view I feel that he did have a point about the root being something which comes up to meet us, rather than something which goes out from us.
The root is subjective in the sense that it doesn't exist in and of itself.
What happens to your lap when you stand up? Does it fly off to Lapland? No, your rootedness, once you have developed it, can be felt by someone pushing against you, but if they are more agile and knowledgeable than you, your root will be gone in an instant.
The root is a dynamic, ever-changing, structural relationship between your body, gravity, incoming forces and the surface you're standing on.
If you only think of it as something which you practice in a static position, a static root is all you'll ever develop.
In this case, your stability will be easily disrupted by anyone who has developed a dynamic root, one that is not lost while stepping, jumping, kicking or throwing (bagua circle walking is good for this).
This in turn is developed by paying attention to your energy while in motion, to keep your centre of gravity low and to manage the distribution of solid and insubstantial throughout the whole body.
My own investigations indicate that rootedness is directly related to whole-brain functioning, where both hemisphere's of the brain are working in synchrony.
I've yet to measure this on an EEG.