Zhou Dunyi in Song dynasty (960-1279) had a famous speach about the picture of Tai Chi. He said: "Moving produces Yang, stillness produces Yin. When moving is extreme, stillness is produced. When stillness is extreme, moving is produced. Moving and stillness are the root of each other". This speach describes that moving and stillness are two basic existing status of any life. Based on Yin Yang theory, Chinese doctors found very early that combining moving and stillness reasonably was important for health. "Moving cultivates the body, stillness cultivates the mentality" has been a essential health concept in Traditional Chinese Medicine.
According to Traditional Chinese Medicine, moving is necessary, but man should avoid to exhaust himself/herself with moving. Sun Simiao, the famous doctor in Tang dynasty (618-907), said: "the method to cultivate health is moving often, but not so much that man cannot bear it". In the classic book of Confucianism "The book of Spring and Autumn", the writer wrote: "moving water doesn't rot, door shaft moving often doesn't have termites, all of these because of moving. The body and mentality are also like them. if the body doesn't move, it becomes stagnant. If the body is stagnant, the person becomes depressed".
In Traditional Chinese Medicine, "still" means not only stillness of the body, but also inner-peace. Ancient chinese had many researches on inner-peace. For Taoists getting inner-peace is even one of the daily excises. Chinese traditional ways to excise "inner-peace" include cultivating morality, cultivating tolerance, removing greed, and a series of physical trainings such as breathing with certain methods, sitting without thinking, etc.
The health concept of combining moving and stillness which Chinese has practiced for several thousands years matches well theories of modern medicine. Modern medicine has proved that negative moods hurt the body, but when man gets inner-peace, all the organs in the body get relaxed and work in their best conditions. On another side, modern medicine emphasizes also that movings/sports are necessary for good health. The reason ancient chinese got understand these so early was actually that they had Yin Yang theory and applied it on everything.
It is easy to find solutions, when man have understood the nature of a problem. Yin Yang theory was the general key for ancient chinese to see the nature of any thing, and have made great contribution to the bright Chinese civilization.