The father of Chinese medicine, Shen Nung, is thought to be the first person to have theorized about circulation in the human body. These theories were compiled approximately 5000 years ago, and led to the development of acupuncture.
Shen Nung developed the idea of the Qi, an energy force that flows through the human body. This energy travels through channels called Meridians which run all through the body. The theory is that when the Qi is not flowing correctly, the human body experiences illness. This incorrect flow can be caused by blocked Meridians which causes unbalanced Qi. In order to reestablish the flow of Qi, certain points of the body where the Meridians contact the surface of the skin must be manipulated. These points are accessed through the insertion of needles into the skin, a practice known as acupuncture. For further reading on this subject, consider reading History of Acupuncture by Leroy Hunts.