Have been thinking more about the “happy hypoxics”. That is multi factorial - like all biological phenomena there will always be extremes in the furthest 1-2% of normal physiology. There is also the fact in a lot of other mammals

The hypoxia response lasts 20 minutes to a few hours and resets, because frankly if you survive that long on a PO2 of 6.5 you’re probably okay. Moreover there is a bottom limit on how low your CO2 can go, due the fact vasoconstriction occurs when too much CO2 blown off

And you pass out. Ionised calcium also falls when you become more alkalotic, so you’d develop muscle, and especially respiratory and cardiac, fatigue.

Fundamentally though, we all survive relative hypoxia when we exercise. (This from the excellent work by Paul Wischmeyer). Once aerobic metabolism exceeded, the switch to glycolysis begins. This is not an oxygen dependent source of ATP.

Cells also undergo a series of internal changes when forced into reducing oxygen conditions. They response to a drop in oxygen before actually being truly deficient in oxygen. So when given warning, they change gene expression.

They stock up on cell defence like pro inflammatory cytokines, anti oxidants, glucose transport and enzymes for glycolysis. They reduce or eradicate efforts regarding DNA and protein synthesis - shift from reproduction to survival.

So you don’t actually -need- oxygen, to produce ATP, in some people. Obesity, exercise, all of these things link into how long you can “work” in terms of physical activity and Mitochondrial ability to oxidise fat for energy.

Will finish thread tomorrow