In order to link this essay to some of the suttas in SuttaCentral I place it here.
Grzegorz Polak discusses the history of the non-Buddhist meditative practices with an analysis of the practice of breath retention as described in MN12, MN36, MN85 and MN100 and it’s side effects in light of various practices in Vedic/Hindu and Jain scriptures as well as modern accounts of the effects of these practices. He shows in this essay that these practices may not have been strictly Jain (Bronkhorst) or Brahmanical (Wynne) but have been part of an altogether other samaṇa movement. He also believes that Uddaka Rāmaputta was a samaṇa.
Grzegorz compares these practices with descriptions in MN14 and MN101, where they are attributed to the Jains. And he looks at description in MN144, SN35.87 and AN6.56 where the side effects of this practice are used to describe a state of a terminally sick person.