So what do you think happens when I tell my adult students that I expect them to 'discard yes and no?' That's right! they all look at me quizzically, bring their faces forward a bit, sometimes tilting a little to one side, and nod 'yes' --Thereby demonstrating that they have no idea what I'm talking about.
If someone I know is walking alone in the distance and I call over to them to get their attention, as they turn they will look first, and then direct an 'I recognize you' face in my direction. With normal vision one can recognize this face from 100 yards away. And even if one has very poor vision, he or she will still display the 'I recognize you' face in return.
Comic Ellen Degeneres has a bit where she waves and shouts to get someone's attention and then realizes it isn't them. It's funny because she reveals how much socially stimulated pain this causes.
The effort it takes to communicate with our faces is usually completely unconscious. But I would suggest to my readers that normal social communication using the head and face requires enormous strength and torso tension. That's why teens and tweens sometimes just drop it. You never actually know if they are listening unless you quiz them afterwards, and even then they may decide not to participate. And the same is actually true for adults, they may be nodding 'yes' without hearing a single thing you've said. It could even happen with a loved one on Valentines day!
At about 6 months of age, babies can lift their head and they are capable of a lot of communicative facial expressions. However, their heads are so big relative to the rest of their bodies that they have to move their chest underneath their head in order hold it up. At some point they also learn to nod 'yes' and 'no,' but if you hang out with 5 year olds you'll see that, although they will give a very attentive 'I'm listening face,' they are often reluctant to nod 'yes' and 'no.' When they do stoop to this adult mode of communication they often exaggerate it with a whole body movement-- undulating with a slack jaw for 'yes,' and shaking horizontally for 'no.'
So. What's the point?
In martial arts and qigong, the head must be included in whole body movement for it to actually be whole body movement. If we are using our head for communication, it is very likely that we are exerting enormous torso tension in order to keep it in that state. As adults, stress is our default position in social situations.
I want to make a distinction here between structural integrity and whole body liquid mass. A person can be holding their head in an 'I'm ready to nod yes or no' position and still have structural integrity. As people age, the quality of the structural integrity tends to diminish, but it may still be there. However, it is not possible to have whole body liquid mass and hold ones head in such a stressful position at the same time.
I suspect that until a student figures out how to get their feet inside their dantian, inside their perception of space, this awareness of the head may be fleeting if it is possible to experience at all. When the whole body is inside the spacial mind it automatically includes the feet and head. It is by looking at the relationship between the torso and the head that, as a teacher, or a dude watching too many sub-standard 'masters' on Youtube, I can tell if a persons body is inside their mind--or not.
The head weighs a lot. Holding it in positions of dominance or submission is a major source of tension. Holding it in positions of dominance or submission is an obstacle to whole body power.