Similar to the theory of yin-yang, qi was derived from ancient Chinese philosophy, which believes everything is related. In traditional Chinese medicine, qi is treated as the fundamental substance of the human body, and its movements explain various life processes. Qi in its physiological sense constitutes, replenishes and nourishes the human body. Qi is often called “vital energy” because it is believed to be the motive energy derived from the essential substance for various vital processes.
Qi is often classified according to what it acts on. For example, the heart-qi refers to the force with which the heart works and the blood circulates, so it regulates the cardiac function; the stomach-qi refers to the force with which the stomach functions, so it regulates the gastric function. The qi that maintains normal functioning for resistance against disease is called zheng-qi, which means genuine energy or body resistance. The qi that warms the body and maintains normal body temperature is called yang-qi, which is similar to the heat energy. Metabolism of materials and energy also depends on the action of qi, including metabolism of blood, fluids and other essential materials.
Qigong is an exercise to regulate the mind and breathing in order to control or promote the flow of qi. Since qi plays such an important role in the vital processes of the human body, the regulation of qi flow is therefore be used to preserve health and treat disease. Medical qigong, the qi exercise practiced to prevent and treat disease, is different from general physical exercise. While physical exercise is aimed at building up health or restoring physical functioning by enhancing strength, medical qigong is focused on the mobilization of functional potentialities by regulating the mind. In other words, physical exercise is purely somatic, while qigong exercise is generally psycho-somatic. Another important difference between physical exercise and qigong is that physical exercise expends energy by tensing the muscles and accelerating the heart beat and respirations, while qigong works to ease, smooth and regulate breathing to store up or accumulate energy in the body.