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How can you simulate `hypoxia`"
Not generally the best source, but good enough in this case:
https://en.wikipedia.org/wiki/Hypoxia_(medical):
Generalized hypoxia occurs in healthy people when they ascend to high altitude, where it causes altitude sicknessleading to potentially fatal complications: high altitude pulmonary edema (HAPE) and high altitude cerebral edema(HACE).[4] Hypoxia also occurs in healthy individuals when breathing mixtures of gases with a low oxygen content, e.g. while diving underwater especially when using closed-circuit rebreather systems that control the amount of oxygen in the supplied air. Mild, non-damaging intermittent hypoxia is used intentionally during altitude training to develop an athletic performance adaptation at both the systemic and cellular level.[5]
I would have thought this explains it :
FSI once offered training (not in the chamber but with a mask and then less and less O2) and we did it.
Maybe I should have said that they offered "hypoxia training".