Deliberate heat exposure and deliberate cold exposure are common practices among biohackers, but these seem to be quite different from the ones in Japan.
First, we don’t do cold exposures so much other than Kangeiko done by martial art practitioners or Takigyo done by Shugendo practitioners. Among health-conscious people, saunas are more common, and if we do deliberate cold exposure, it is done with a sauna, as a form of the cold bath, not an ice bath.
The length of staying in a sauna is different, too. We usually stay between 6 to 12 minutes, while you seem to stay up to 20 minutes and sometimes even up to 30 minutes.
When I heard that, I thought it was impossible to stay in a sauna for 20 minutes, so I tried doing it and this is what happened to me.