The following article on 'Chinkuchi' can also be found at David Evseeff's site on Isshinryu karate: http://grove.ufl.edu/~devseeff/listserv.html .
Lt. Col. Charles Murray wrote this article in 1971, when he just came back from Okinawa.

Rememberances of Okinawa:
Chinkuchi

By Lt. Col. Charles Murray (USAF)

 

One night after a rather exhaustive workout at Master Shimabuku's dojo, I and several other students were drinking tea that the Master's wife had brought us.  In the course of the conversation that accompanied the tea drinking, the instructor, Master Shimabuku's second son, Shinsho (Ciso), was telling me of how he had once threatened to kill an attacker with one punch.  As he began to tell me this, I smiled.  When he asked me why I was smiling, I told him that I didn't think that anyone could kill another with just one blow.

As I spoke, I guess that I was thinking that if there was one thing that American karate had taught me was that you could not kill with one strike.  I mean, who is strong enough to do that, who could generate that kind of power?  Did not kickboxing show us that that was impossible, that the "one-strike kill" was just a myth?

Almost in reply to my thoughts, Master Shinsho struck me twice. With his first blow, a nukite (spear-hand thrust), he temporarily paralyzed my arm; with the second blow, my leg.  At that moment, I realized that there are some people who can kill with one strike!  I asked Shinsho, who was now standing and laughing, how he did that.  He replied that his power cam from chinkuchi and that he would show me more the next day.  That was my introduction to what the Okinawans call chinkuchi, and I could not not wait to learn it!

The next day I found out that only three Americans before me had ever been taught chinkuchi and out of the three, only one at that time had mastered it.  The man who had mastered chinkuchi was from Florida named Bob Bremer.  Master Tatsuo Shimabuku swore by this man's abilities, and acclaimed him as the best Isshinryu fighter in the world.  He said, "Bremer Number One, Nagle Number 2."  It was funny, but not long after hearing of this man, I saw in a karate magazine where he had beaten Parker Sheldon for the championship of a big tournament in the South.  The article mentioned that Bremer's movements looked slow until they suddenly locked in place with devastating power.  This came from chinkuchi training.

Well, what is this chinkuchi?  I should first say that the word is unique to Okinawan karate and has never been officially defined by even the Okinawans.  It truthfully has no meaning and many meanings. Chinkuchi is both a way of training and what is achieved when one is able to achieve the main physical goal of karate which is to be able to block and counter simultaneously with killing power.  It is the way the Okinawans achieve power through karate-do.

This "power" (chinkuchi) is developed by striking with:

(1)  Proper tensing
(2)  Proper breathing
(3)  Accompanying each movement with what I call "mind control."

Tensing:  In karate when we punch and kick, we initiate a movement by swiveling our hips.  This swiveling creates a shock wave which finds expression through our striking joint (as we lock  our arm or leg into place).  It is then transferred to what we strike; through our striking surface (e.g. first two knuckles, ball of foot, etc.).  Let me illustrate.  When we punch we "swivel" our hips.  This creates a shock wave which travels from our hips up to our shoulder and as our arm locks into place goes out from our first two knuckles.  This power flow that I have just described, in order to be effective, must be accompanied by such things as:

(1)  Being loose until the moment of contact (30% tension)
(2)  Proper breathing
(3)  Mind control or allowing your ki to flow through the movement.

This method of proper body tensing is an ingredient that must be mastered for a person to have chinkuchi in a movement.

Proper Breathing:  Every Isshinryu student knows that a kiai is among other things a shout of spirit.  It is used because:

(1)  The body's striking movement is always stronger when one exhales properly.
(2)  It has the capability of momentarily stunning an opponent. 
(3)  It tightens the abdominal muscles as one strikes, thus aiding in preventing one from experiencing pain from a counter blow.

What few students know is that something like a kiai should accompany every strike in karate (either a silent or audible one).  In other words, with every strike one should exhale from the diaphragm. This is a brief description of what I call "proper breathing."  A further description of proper breathing would be an article in itself.

Mind Control:  The third aspect of chinkuchi and the most important (and least understood) is what I call "mind control."  This is known in other martial arts as qi, ki, inner power, the spiritual aspect of karate-do, etc.  This aspect of Okinawan power training (chinkuchi) is virtually unknown, I feel, by our Isshinryu sensei today.

Last year in speaking with an Isshinryu hachidan (8th Dan), I asked if he had ever heard of chinkuchi.  He said that he had heard of it from Mr. Bremer (mentioned previously), but our conversation revealed that about all he knew of it was the name.  You might ask why this is.  The answer is simple.  Master Shimabuku could not speak English very well so it was impossible to communicate it to the Americans who studied exclusively with him.  All of the Americans, that I know of, who were taught chinkuchi studied with Shimabuku's second son, Shinsho, the only one who could speak English well.

Well, let me get back to "mind control."  This mind control, coupled with proper tension and breathing, give the karate-ka was masters chinkuchi, additional power.  Perhaps the best article that I have ever read on what this mind control is was in an article in Official Karate magazine several years ago by Howard Taque from New York.  In the article, he defined qi, ki, etc. as a form of "self-hypnosis." For more information on this, see the aforementioned article.

But now the question is:  how do the Americans train?  The answer in a nutshell is all differently.  Some Americans achieve power in their techniques by using strength and weight in their movements much like a boxer.  Some try to incorporate tensing and breathing in that they have a vague notion of how they should breathe and tense.  But, truthfully, only a few American Isshinryu sensei that I have seen know how to achieve power in any way, right or wrong, American or Okinawan.  They act like whatever will be, will be.  If their students gain any degree of power from training then that's good; if not, well, it's the student's fault.  The student must not be training hard enough, or something.

The real difference, however, in American power trianing lies with mind control.  It seems that no one know anything about it.  I have never seen anyone really train to master it.

Well, this is dragging on.  Suffice it to say that there is an organized, proven way of developing power that the Okinawans call chinkuchi. This chinkuchi is taught to the beginning Okinawan student, but because of communication problems has never been taught to most Americans.

The last question that I will address is:  why was chinkuchi important to the Okinawans?  It was important because Te was developed in Okinawa as the Okinawans were fighting a guerilla war against the Japanese.  I assume that there were times the Okinawans only had one punch or kick to give their oppressors.  If this strike did not kill or disable they were in danger of being either killed or disabled themselves.  It not only was important, it was all-important.

Well, allow me to end this article with the following story that I recently read in Black Belt magazine.  It illustrates graphically what can be achieved through chinkuchi.

One day, an old man walked into a dojo in Hawaii and saw the students hitting the makiwara.  He watched as they continued to strike the makiwara (the "American" way), and he began to smile.  The old man's smiling annoyed the students and they asked him if he would like to try his luck at striking the makiwara.  The old man said "okay," took his stance, and threw his punch.  It broke the makiwara completely in half.  It seems that this old man had been one of Gichin Funakoshi's first students.  Master Funakoshi, an Okinawan, had obviously taught him chinkuchi.