**3. Qi and diseases**

According to TCM, "Qi is the root of the human"; "All the diseases originate from Qi." Qi dominates the whole vital activities. Qi can make the human body work in an orderly fashion by promoting a variety of physiological activities; "Qi deficiency" will lead to a decline of physiological functions. As one part of a central medical classic *The Yellow Emperor*'*s Inner Canon*, "Plain Questions" pointed out that consumption of the vital Essence Qi leads to deficiency. The basic idea of TCM to prevent and cure diseases is strengthening vital Qi to eliminate pathogenic factors. Strengthening vital Qi can improve body's resistance to disease, in order to eliminate weakness syndromes, ward off illnesses, and be physically strong. On the understanding of the etiology, TCM theory emphasizes the cause of disease—"vital Qi deficiency"—especially.

Xing-Tai Li proposes a scientific hypothesis that "Qi is bioenergy" [1] and Qi deficiency can lead to bioenergetic dysfunction, which can be improved by Qi invigoration and demonstrates that Qi invigoration was achieved through improved mitochondrial bioenergetics [2].

The central player in bioenergetics is the mitochondrion. Bioenergetic dysfunction is emerging as a cornerstone for understanding the pathophysiology of mitochondrial diseases. Mitochondrial dysfunction would undermine the function of cells, tissues, and organs, thereby causing cancer, diabetes, obesity, strokes, cardiovascular diseases, neurodegenerative diseases, aging, etc. Currently, there are no effective treatments, yet the causes of these diseases remain a mystery, while their incidence and morbidity either remain constant or are increasing. Huge investments in biomedical research in recent years have resulted in some striking accomplishments but have failed to reveal the anticipated causes for the diseases. Western medicine is in crisis [3]. According to TCM, Qi deficiency is the common cause of these diseases. Therefore, Qi-invigorating therapy can be used for mitochondrial diseases [4].
