Ki (or Chi - Chinese) are central to many martial arts.  In fact, two martial arts use the term in their name: Aikido and Tai Chi Chuan.  The notion of ki will be explored in two articles below, detailing the historical development and usage in martial arts training.

Before embarking on these two topics I first wish to tell a story.  I took a number of classes in Tai Chi where chi became a central topic of conversation.  On one occasion, the master said that people should not think about chi as if it is something special...it is like air...all around us.  Then, he replied to questions about the location of chi in the body, in the center of gravity normally assumed to be 2 inches below the naval.  He explained that the real center of gravity is in a central point on the left foot when one's weight is on the left foot, and in the same location on the right foot when their weight is on the right foot. Some time afterwards, he updated these comments and said the real center of gravity is in the nose.  Being Jewish, I naturally had to ask whether that particular instruction would apply equally to Jewish people as to say Chinese.  For example, in my case I was concerned about becoming top heavy...

On Ki: History

"The original idea of ki developed as a metaphysical principle in a number of Chinese schools of thought.  Ki was, for example, the essential principle of harmony, and it was the source of creativity expressed in the form of yin and yang (Lao-tzu), the vital fullness of life (Huai-nan-tzu), the courage arising from moral rectitude (Mencius), the divine force that penetrates all things (Kuan-tzu).

As a term, it was never clearly defined.  Sometimes it was equated to empty space (the void) or nothingness (Lao-tzu), at other times to the formative energy emerging out of chaos (Chuang-tzu).  It was regarded by some philosophers as the dualistic principle that structures the universe...this dualism evolved into the ki operating as yin and yang, darkness and lightness, from which arose the Five Elements Theory and the divinations of the Book of Changes."

"The primary metaphysical principle of ki was introduced into Japan in the Nara (710-94) and Heian (794-1185) periods and generally upheld, but the introduction of Buddhist thought from India to China affected its meaning, due particularly to the idea of karmic retribution.

More significantly, the idea of ki combined with indigenous views of nature responsible for the cyclic process of growth, budding, flowering and the withering of plants and trees...

The most dramatic changes in the interpretation and application of ki began to take place with the rise of the samurai class from the late Heian period...reaching its apex in the early Tokugawa (1603-1868).  The samurai who faced constant threats of death in an age of warfare understood ki in terms of courage, shi-ki; will power, i-ki; vigor, gen-ki; and bravery, yu-ki.  They were also concerned with equanimity, hei-ki; and conserving energy, shu-ki; which attempted to prolong breathing, ki-soku, as a matter of life and death..."

Ultimately, O'Sensei discussed his ideas of ki: "...I saw clearly that human beings must unite mind and body and the ki that connects the two and then achieve harmony with the activity of all things in the universe."  Later, "When one unifies mind and body by virtue of ki and manifests ai-ki [harmony of ki], delicate changes in breath-power occur spontaneously and waza [proper technique] flows freely."

According to Kisshomaru Ueshiba, "[the unity of individual-universe] inherits the idea of ki held by the ancient Chinese masters... [the free, spontaneous expression of breath power] teaches that a person's breath controls his thoughts and bodily movements...The reason for Master Ueshiba's emphasis on the dual functioning of unity and spontaneous expression is that he saw the essence of ki as being the essence of his budo."

[Quotations above from Spirit of Aikido by Kisshomaru Ueshiba pg 21-25 - [bold brackets my own]]

As Aikido continued to develop, unfortunately, the term ki became a political football.  Koichi Tohei, a top student of the founder, separated from the founder's organization (Aikikai) a few years after his death and formed his own style of Aikido, called sometimes ki-Aikido or Aikido with mind and body coordinated.  During his years under the founder, he was known for giving detailed and clear explanations of ki.  While O'Sensei gave primarily mystical explanations, Koichi Tohei explained ki almost as a mathematical formula, easily understandable by contrast.  The Aikikai responded by virtually writing Koichi Tohei out of the history of the organization and cleansing the term ki out of the records of instruction.  Meanwhile, Koichi Tohei's trademark became the ki of his Ki-Society, and while many aikido masters left the Aikikai for his organization in the early 1970's, they all left in droves beginning in the 1980's.  Fumio Toyoda Sensei was one who followed this path, later to rejoin the Aikikai.  We now have the relics of this political strife in our midst.  For years training under Sugano Sensei, the term ki was never to be heard.  It simply developed naturally with practice and there was no need to discuss it.  Under Toyoda Sensei the training left from Koichi Tohei, considered to be a valid method, continues on only absent the word ki as it is replaced by the term energy in daily practice.

When asked once about all the different teachers in Aikido and their political strife, Sugano Sensei wryly commented how strange it must seem to outsiders for us to call Aikido the art of peace.  They then observe how we all fight vehemently over who is teaching the real art of peace.