Once again, it is so good to read this encyclopedia to learn some facts and details from past time which are reliable lighthouses to lead to present day. Two quotes from the article written by an outstanding sinologist Catherine Despeux look better with Traditional Chinese and tones in Pinyin and dates. (I have to say that recently I have found yet another interesting book, A History of the Japanese Language by Bjarke Frellesvig and every time he speaks on Chinese intersection he uses tones but that’s totally another story).
“Methods for circulating breath are attested during the period of the Warring States (403-221), became well known during the Six Dynasties (220-589), and developed during the Tan (618-907) and Song (960-1279) periods. Their most ancient source is an inscription dating from ca. 300 BCE that describes the circulation of breath throughout the body (see Harper 1998, 125-26). In the Han (202 BCE-220 CE) period, circulating breath is mentioned in several texts, including the Huángdì nèijìng (Língshū 靈樞, sec. 11.73).”—Catherine Despeux.
“Circulating breath is often associated with gymnastics (dăoyĭn 導引) and breath retention (bìqì 閉氣). It is generally performed in a reclining position for 300 breaths, before one expires the breath slowly and inaudibly. One begins with retaining breath for twelve breaths (the so-called “small cycle,” xiăotōng 小通), and then progresses up to 120 breaths (the “great cycle,” dàtōng 大通). Tang documents add to this classical model a circulation of inner breath in which Intention (yì 意) plays a major role.”—Catherine Despeux.