The classical Chinese explanation is that channels of energy run in regular patterns through the body and over its surface. These energy channels, called meridians, are like rivers flowing through the body to irrigate and nourish the tissues. An obstruction in the movement of these energy rivers is like a dam that backs up in others.
Acupuncture is one tool used to restore the flow of Qi, by inserting needles into the acupuncture points (located on the meridians). These insertions are said to clear any residing blockages, or dams, thus freeing the river to better feed the body in its entirety.
The meridians can be influenced by needling the acupuncture points; the acupuncture needles unblock the obstructions at the dams, and reestablish the regular flow through the meridians. Acupuncture treatments can therefore help the body's internal organs to correct imbalances in their digestion, absorption, and energy production activities, and in the circulation of their energy through the meridians.