Yang Disease is the problem of people sagging their chest, it is not unique to people who practice Yang Style Taijiquan we see it in other styles too.
Why do people sag their chests?
Perhaps because students have too closely imitated the most revered Taijiquan teachers, who are old and a little broken from too many years in a human body.
Or perhaps because American men often puff up their chests to show prowess and the first thing their Taijiquan teacher says when they walk in the door is, "You waste Qi. Big chest no good. One Chop Finish!"
Or perhaps it is a mis-conception about the idea of having "ward-off power" in all directions. Caving the chest with the wrists out in front makes the body a kind of bell-like shape.
It's also possible that most Taijiquan practitioners simply spend more time reading books and staring at computer screens than they do standing up straight.
But I have a better explanation! The Taijiquan classics have a line which is very often quoted, "The spine should be plucked up like a kitten being carried by its mother." I think people are imagining having a cat biting them on the nape of the neck and pulling them upwards, which would naturally pull the chest inwards. (They often over tuck the pelvis in a compensating motion too.) The problem with this image is that when a kitten is plucked up by the nape of its neck, the kitten is on all fours, so the equivalent in an upright human is actually being plucked backwards. And that can't be correct either.
When a kitten is plucked up, its arms and legs are drawn inwards. That is correct. The plucking action starts where the mother cat bites and stretches the kitten's flesh equally from the head to halfway down the spine and from one shoulder to the other. The bite happens in the center of a diamond (or a cross) which has its corners:
- Half way down the spine
- At the top of the head
- And at the outside curve of each shoulder
This soft structure is actually like a diaphragm or a trampoline. The whole diamond shape can function as a single structure, to be expanded or drawn together or just relaxed.
But obviously the image of a kitten being plucked up is confusing. There is a better image! In Orthodox Daoist Meditation we use the following image for part of the invocation of the Perfected Warrior, Ziwei:
- His hair is woven with silk cord and chain (to protect against sword cuts); one half of his hair is in a thick braid going halfway down his back, the other half is in a loose "throw" scattered about his shoulders.
- Floating loosely off his shoulders and halfway down his back is a silk scarf.
- On his chest can be seen gleaming bronze armor showing through his robes.
If you followed the link at the top and were to read through all 56+ comments on Formosa Neijia you'd see that I don't believe stretching will help the problem of a colapsing chest. Likewise various scemes involving strengthening this or that, or pulling the shoulders back will not help. The idea that the purpose of an exercise is to fix something is a fool's erand. Feel the problem internally and just change. Be resolute. The purpose of an exercise in internal martial arts is to teach you what you are doing wrong. Now just stop doing it wrong.