閉氣 bì qì
Time of origin of this exercise is probably the Han dynasty (201BCE-220CE) or later, and time of execution during the day is time between midnight and midday (‘living breath’— shengqi 生氣). Of course, daoyin physical exercises included retention of breath as well as martial arts training (for example, archery, or knife throwing etc.)
Breath retaining and counting to 200, 250, or 300 in meditation practice seems unrealistic but the good news is that within gymnastic exercises it was reduced only to 5, 7, or 12. There is another thing which was interesting to learn from the Catherine Despeux’s entry, I mean a source of a very old image of ‘a feather placed under one’s nose which should not move’ while retaining his breath. I really do not remember when and where I had read about it the first time (some decades ago) but now I know exactly that it was quotation from the Prescriptions Worth a Thousand—Qianjin fang by Sun Simiao (fl. 673), many hundreds years ago.
I live in the place where climate is mostly (9 or 10 months rather) cool and cold, so many years ago I made it the Golden Rule for myself: always inspire through the nose and expire through the mouth in the street. Doing daoyin gymnastics every morning and sometimes in the evening, running in the mountains and in the park and throwing knives seem helpful enough to avoid illnesses and keep myself working and organized 12 months in a row 🙂