[ultrarunner]

I run all summer in the afternoon. Up to 106°F is fairly comfortable, 107°F feels tolerable, and >108°F is very difficult. It really does feel like it falls off that quickly.

However, I have done this for years. I sweat a lot more, and a lot more quickly, than I used to. There have definitely been both long-term and beginning-of-the-season acclimation periods, and it's a bit of an understatement to say that not everyone is interested in pursuing this. The result is major trailheads being closed in certain conditions due to tourists routinely collapsing, needing rescue, or sometimes passing away. This despite the fact that there are many of us locals who are fine within our limits (that we know and have learned to respect).

Those guys in the Quickielubes have a swamp cooler going at minimum, are acclimated, out of the sun, and are still uncomfortable. The landscapers are up at 5am and disappear as the temps climb. We'll be in the half that don't end up in the ED.

[paulryanrogers]

Different people have different thresholds. I cannot function well above 80F in humid weather. I get dehydrated very quickly with a small frame and heat exhaustion in short order.

[ultrarunner]

At any given time, yes. My thoughts above are somewhat rambling, but what I found most interesting was the adaptation over time. I'm sure that capacity for adaptation is variably effective amongst different people as well.

[fnordpiglet]

Definitely. I’m unable to function above 72F. That’s because god made me a programmer.