Probably the first "internal" exercise I ever learned when starting to study any of the Wutan(g) martial arts from Liu Yunqiao line.
This clip provided the subtitles in Chinese as to what Liu is saying. He indicates that this is to be done after you have completed your workout - He says that this is what Li Shuwen did and of course, that is where he learned it from - there are other similar exercises as part of Liu's bajiquan curriculum - a lot of this has to do with breath work and relaxation and the natural development of reverse breathing.
https://www.youtube.com/watch?v=sQDkMibmoL8
八极拳宗师刘云樵先生的养气还原,全网唯一中字字幕版
The restoration of Qi nourishing by the master of Bajiquan, Mr. Liu Yunqiao, the only Chinese subtitle version on the entire network