Aside from the obvious safety concerns of heat exhaustion, heat stroke, heat prostration, etc., what is known about the detriments or benefits of exercising at higher-than-comfortable temperature/humidity?
To put it concretely, the gym I currently use has a room temperature these days of perhaps 75 F, with fairly muggy humidity. I find that much higher than I'd prefer to exercise in, particularly for running on a treadmill (at a 7:30--8:30/min pace). I would ideally enjoy 66 F with low humidity, At the current temperature/humidity I sweat profusely and have been backing off of my previous exertion on the treadmill out of basic caution, though it strongly feels I could continue at a higher exertion without any risk of serious harm. (I am well hydrated and have never felt close to dizzy or anything like that--just tired. And hot.) But I am concerned about less obvious harm...
And so, what I want to know is: is there evidence to show that sustained hard exercise at higher temperatures/humidity has any subtler systemic harm (that is, subtler than the obvious ones listed above)? I mean, is it "bad for your brain" Or other organs? Does it put too much stress on your system?
Or is training in conditions in which sweating is profuse and sustained actually good training in some sense? Such as training your system to be more efficient or other benefits?