Shiatsu is practised with two hands. While one remains static and receptive (yin hand), the other one applies pressure along a meridian (yang hand). The idea is to create a current in between the Yin hand and Yang hand-flow of Qi. Qi can be interpreted as the electrical current between positive and negative charge or the magnetic field between positive and negative poles.
Meridian lines are defined as channels of living magnetic energy in the body. Meridians have been shown to possess higher electrical conductivity than surrounding tissue, therefore bioelectrical flow happens easier in these pathways. Under healthy conditions, the Qi energy flows freely through these meridians in a balanced state. According to Oriental thinking, when abnormal functioning of the internal organs or abnormal external stimulation occurs, energy stagnates in the meridians and produces sickness. Therefore in order to restore health, the energy must be released and normalised.
The condition of QI energy in the meridian lines is defined by kyo and jitsu. These concepts are very similar to yin and yang. Kyo is the state of depleted energy and hidden potentiality, while jitsu is the condition of excess energy. Shiatsu is working with total functional problems of the meridian lines, which can originate in the body or the mind.