Shiatsu acts on the subtle anatomy of the body described as qi in Chinese or ki in Japanese. Qi is a fundamental concept of the traditional oriental medicine and is considered as our "life essence" which maintains and nurtures our physical body , mind and spirit. In traditional Indian medicine it is described as prana. Qi is everywhere. It moves and changes quickly from moment to moment and can easily be replenished on a day-to-day basis. The human body is a field of continually moving energy, circulating through cells, tissues, muscles and internal organs.

The Chinese word qi translates as "breaths". A Japanese dictionary defines qi as mind, spirit, or heart. Japanese vocabulary has hundreds of expressions which use the word qi, most of them ordinary ways of talking about human moods, attitudes, or character. Qi is often characterized as energy.

Within the organ and meridian systems, energy is constantly being exchanged. The energy circulates to fill areas where it is lacking (Kyo) and drain off areas where it is excessive (jitsu). The entire system is designed to be self regulating. Most energy imbalances correct themselves without effort. Treatment is only required for stubborn and persistent blockage or lack of energy in a certain area, which is where Shiatsu and related disciplines come in.

There are a variety of exercises you can do to experience qi and feel its effect on your body. Qi is a real force, made up of electric, magnetic, infrasonic and infra-red vibrations, which can be intuitively perceived and mentally directed. It can be photographed using Kirilian photography. Like air that we depend on for our life, qi is the very source of our vitality. It is the force within us which gives us initiative, which drives and inspires us to move forward in life. When the qi leaves us, we die. According to the ancient philosophers, life and death is nothing but an aggravation and dispersal of qi.