https://pubmed.ncbi.nlm.nih.gov/23411620/
That one was 80-90C, which is a really hot sauna.
And maybe Finns don't go to sauna when they plan to conceive? Does Finland have a lower rate of unwanted pregnancies?
I went to sauna 3 - 4 times a week, ex-girlfriend got pregnant 2 month after cancelling the pill (while I still went to sauna)
For the record, if you're not acclimated, intense heat exposure is a lot more agonising than 30 minutes of exercise for less benefit. If you haven't experienced a properly tuned sauna in your life you are in for a ride. What's being studied in the literature is nothing like your standard hotel experience.
> intense heat exposure is a lot more agonising than 30 minutes of exercise for less benefit
Having to do absolutely nothing other than not leaving is quite different from pushing through a physical activity that can also easily be causing all kinds of discomfort.
by the rules of this universe, you can't survive being submerged in 40C water for a prolonged period of time (even 37C would kill you as well), because humans produce heat and if you can't dispose of it you'll overheat and be dead soon enough