What exactly is reverse breathing? Is it actually baby-like breathing? Do the kidneys actually "grasp" the qi from the lungs? Does the mingmen (lower back) expand to suck air in? Does the bellybutton go in with the inhale or in with the exhale? And what does it actually do? Why breath in reverse?
It is actually quite simple.
Normal breathing happens in the lungs, the diaphragm goes down, the ribs open to the sides, and the bellybutton doesn't change much. When it is conscious, we just think "suck in" and "breath out."
Reverse breathing is when we move the body first, movement forces the breath inward, and then movement forces it outward. The breath begins by expanding the ribs to the sides. Most people can get this far on the first try.
Cheetahs can run fast because ligament structures connect their diaphragm to the action of their legs, which passively forces huge amounts of air into their lungs. Humans have this ability too, but it requires a particular engagement of the legs. It is more than a simple bending of the knees or squatting. To make this process conscious requires relaxing the legs and sinking downward while paying attention to the passive effects on the breath, and then playing with the result until it can be coordinated with the active-conscious opening of the ribs. It isn't hard.
What is challenging is the exhale. Once the lungs are expanded, an autonomic or habitual forcing of the air outward tends to take control. So the inhale is "reversed," but the exhale is just normal.
To get fully reversed breathing, the spatial mind must initiate the inhale from outside the body. (Regular readers of this blog will be familiar with this idea.) In this case a simple way to proceed is to look at the canopy of a tree above one's head. Imagine that the leaves are breathing, going up and down, and out and in. The visualization must sync up with the actual movement of the body.
By this method it is possible to delay the exhale without creating compression. The spatial mind (outside the body) can easily delay the exhale if it is more than six feet away from one's actual body. If the spatial mind is too close to the actual body, it will force a compression of the ribs. Compression involuntarily forces the breath outwards.
Anyway, that's it, that is reverse breathing.
Why do we want to avoid the involuntary compression of the ribs? There are probably a lot of reasons, I will try to address a few. First, that exhale is used to solidify our identity, and the goal of acting and martial arts (as enlightenment) is to free oneself from any fixed identity--especially identity fixed by rigidity in the physical body. The second, is that communicative social-methods of communicating power, all tend to rely on this forced compression exhale. We want simple power, not socially expressive power. Socially expressive power is used for domination and submission.
That is what I have to say on the subject, but I would like to open it up to others who may have something to contribute here.
Here is a wonderful article about, vagal tone and the vagus nerve: http://mosaicscience.com/story/hacking-nervous-system
Vagal tone is measured by the ratio of the heart rate during the inhale over the heart rate during exhale. A slower heart rate during exhale indicates greater vagal tone.
Vagal tone is associated with a better functioning immune system. So that is the big question, how does reverse breathing effect vagal tone? And I'm sure readers can think up all sorts of related questions.
Go for it!
Perhaps a little more contextual explanation will help explain the confusions about reverse breathing. In the early twentieth century in China, there was a big push to medicalize Chinese healing practices. Concepts of health were as much about religion as martial arts were; that is, they were a single subject. Both were squeezed into anatomy and physiology. The Red Cross and the YMCA were models used in China to make tradition seem more modern. Reverse breathing was probably connected to Daoism, and Daoism was trying to make itself into a philosophical practice by discarding content related to gods. This was framed as a search for "essence" or "refinement," this may have made the practices more accessible (especially in the West), but it also diminished them.
Originally there were two gods, Heng and Ha. Not a lot of research has been done on them, but I suspect they were weather gods (technically a type of "thunder god"), one who breathed in "heng" and one who breathed out "ha." Naturally people knew about these two gods because there were comic stage routines based on the hilarity of someone who can only breath in or only breath out. Somehow this relates to reverse breathing--medicalized versions of Heng and Ha as "exercises" can be found in numerous modern qigong books.
Here is a cool tid bit I just grabbed from Chinese History Forum:
As for the name "General Heng and Ha 哼哈二将", they originated from Ming dynasty novel Fengsheng Yanyi 《封神演义》 (The Investitures of the Gods). The author based them on two Buddhist door guardians. Both of them were fierce and brave. They generally became Chinese folks figures because of this novel [Editor's note: most likely the "novel" is a collection of rituals that already existed].
One was called Zheng Lun 郑伦. He was able to spit out white breath from his nose to kill the enemy. The other was called Chen Qi 陈奇. He was able to spit out yellow breath from the mouth to kill the enemy. [Editor's note: Extreme nose phlegm and halitosis?]
You can see these figures in many Buddhist temples of China [Editor: Most of these were made in the last ten years]. Shown below the figures outside the door of Buddhist temple Eastern Mountain in Beijing 北京東嶽廟 [Editor: A key temple connected to Fengshen Yanyi, and most likely the history of Baguazhang.]