“Sink the chest, raise the back (合胸抜背)” are the words that Taijiquan practitioners may commonly know. It is one of the important teachings so I would like to explain it in my own views.
If we, people, go back to the evolutionary process, we originally had four legs.
It is natural that the position of the shoulder shifts forward if you hold your hand forward.
However, the spine and neck muscles must be straight.
This posture is called “Sink the chest”. It is not stoop.
In martial arts, there is no posture to stretch the chest with the thorax open.
If you hold your chest up, the center of gravity will rise and not stabilize.
In the posture of “Sink the chest”, the thorax is kept closed and Qi (energy) fell to Dantian (body center).
But here, “Raise the back” is a more important concept.
Even in the state of inferior battle, the back loosen free must be kept.
Being “Raise the back” means that the spine is smoothly rotating without friction.
If we are not in the state of “Raise the back”, we could not learn the martial art techniques.
If you are a student who is able to be “Raise the back”, you can be taught while your instructor is touching your shoulder lightly.
However, this may be a courteous teaching method.
In the old days, the master told that the technique was learned with seeing. If you can only acquire skills by just seeing it, you are a genius or have already reached the same level.
If allowed, it is better to stick with your hands to the back of the master like a shadow man.
How to convey force and timing will appear at the back.
However, such as touching the teacher ‘s back, even the inside students are not usually allowed.
The most scare thing is that the back is hardened with fear or inferiority during battle.
It is the same as “getting over” in martial arts.
If it is a battle with real swords, it will directly lead to death.
If you confront a strong enemy, you must put out your intentions and have to pull up your back.
“Sink the chest” and “Raise the back” are the two sides of the same posture. “Sink the chest, raise the back” is a posture to keep in any situation of battle.