The positive effect of training in High Heat conditions have been known for quite some time now; however, the message seems to be falling on deaf ears. We're always hearing of how dangerous it is to train in high heat/humidity...and it is, but this is not a reason to avoid these conditions, rather it's a reason to condition oneself to these conditions. I just can't believe how often I hear people talk about needing to get their run/ride in before or after the hottest part of the day, because of the perceived danger, despite the evidence of how beneficial this type of training is on the body.
I feel lucky in that every year where I live, it's common to exceed 100 degrees in the feel-like temp and I don't avoid it. The fact that it slows you down I see as an additional benefit, because I'm the type of person that always over does it (like most of us), both on the bike and on my runs. So, in addition to using high heat runs/rides to build
oxygen-carrying capacity of my blood, I can use them to slow me down, ensuring I can do my runs/rides day-after-day. I can very much feel a difference when the weather cools.
But people are slowly starting to come around to the many benefits of high heat training, like this lady from Sweden