Too hot, what is your cut off for when you are no longer gaining aerobic benefit? It seems like it might be higher than what Gordon, myself and others consider valuable.
For me, I'd say it is around 60% max HR, which would put me around HR 120. Canova's regeneration runs are based off percent of race pace, and the quick end of that would be around 8:10 or 8:20 a mile for me. At those paces I'm usually around HR 130.
I am definitely working aerobically at those efforts, but I certainly don't run at them all the time. Not even most of the time. But they strike me as the easy effort that Lydiard said would be fine, but would just take a really, really long time to gain benefits from.
As a side note, some of the biggest aerobic monsters I've ever known were from my years living in Arizona trying to hang with dudes who primarily spent their time hiking. Lots and lots of hours in the mountains and canyons just cruising around, but they could go forever. They could jump into long trail runs or on a mountain bike and still crush it. Sure, they didn't have the efficiency/economy/practice to run a fast 10k, but the foundation for it was definitely there.