Qi (Chi) (simplified Chinese: 气; traditional Chinese: 炁; pinyin: qì) is the invisible life force or vital energy that flows in all living things, including in the human body. And its movements explain various life processes. Qi in its physiological sense constitutes, replenishes and nourishes the body.
Qi is formed from inhaled oxygen, dietary nutrients, and inborn primordial qi stored in the kidney, which may be genetically related. It circulates along the body’s meridians (energy channels in the body) and collaterals. The smooth flow of Qi is crucial to maintaining a balance among one’s physical, emotional, mental and spiritual realms, hence creating a healthy body. All meridian therapies aim to enable smooth Qi and blood flow. Insufficient Qi and blood, or obstructed flow makes one frail and induces various physical or mental disorders. Emotional instability may cause the stagnation of Qi. For example, anger may lead to dizziness, headache, distress in the hypochondriac regions, or distention in the stomach with poor appetite.
Qi is often classified according to what it acts upon. For instance, the heart-qi (simplified Chinese: 心气; traditional Chinese: 心炁; pinyin: xīn qì) refers to the force with which the heart works and the blood circulates, so it regulates the cardiac function; the stomach-qi (simplified Chinese: 胃气; traditional Chinese: 胃炁; pinyin: wèi qì) refers to the force with which the stomach functions, so it regulates the gastric function. Metabolism of materials and energy also depends on the action of qi, including metabolism of blood, fluids and other essential materials.
Another classification is zheng-qi or right qi, which maintains normal functioning for resistance against diseases; and xie-qi or evil qi, which causes diseases.
According to yin-yang theory, there are two types of Qi in the body: yang-qi and yin-qi. A balance of yang-qi and yin-qi is essential to health.