From what I’ve gathered, it is more useful to work off your RPE and the pacing which corresponds to your AeT/AnT because you will not be capable of keeping your HR at these levels under excess heat and humidity.

You don’t seem to be suggesting it, but attempting to work at the upper end of your thresholds under these conditions is at best ineffective and at worst hazardous because you won’t be able to sustain the muscular load normally required to hang out in these pace zones but you will be stressing your heart.

I’d be curious to see what the coaches have to say, but as a training effect I think training in heat makes you better at running in heat. It’s like putting in the hard hours of altitude training without the perks!

Anecdotally, being in Texas, I have found that running through the summer I’ve been having an easier time running through the early fall, but again only because it’s still hot. It hasn’t made me any faster or improved my thresholds any more than just the work on its own.

I often see significantly elevated HR for a given pace when the temps are high. In hot weather the capillaries in the skin dilate to help you shed more heat to the air. That means more blood shunted to the skin and less available for the working muscles. The effect is the both perceived exertion and HR are higher than you would normally expect. While the HR is higher the muscles are still propelling you at you same old Z1-2 pace so they are getting the same training effect as Z1-2 in cool temps but the overall stress on your body will be like a long Z3 workout and need more time to recover.

I suggest slowing and waiting for cooler weather unless you find you are able to recover well from day to day.

Scott