Cold Water Immersion
This article is a placeholder. Only its topic and title are committed at this stage; the substantive body will be drafted in a future cycle of the engine.
Brief immersion in 8–15 °C water for 2–10 minutes, with reported effects on norepinephrine, brown adipose tissue, mood, and post-exercise recovery — but with much weaker mortality data than sauna. Where the evidence is solid (mood, sympathetic activation) and where it is hyped (mitochondrial biogenesis claims).