https://www.53x12.com/training-at-altitude you can thank me later for this one but take it with a grain of salt because it was written by an infamous mad scientist who is now banned from the sport. Scroll to the bottom for the important points. Too funny, most of the athletes he is touting were notorious dopers, so using high altitude training and their most probable EPO programs, well there is nothing to be gained there, unless that is your program too..
And what he actually discovered, but probably did not realize, is that people are very different when it comes to altitude. From what I have read lately, there are 3 groups, those that get worse, those that stay even, and those that benefit. And far as I can tell, the only way to know which group you are in, is to go and do the work up high and see what happens. I'm one of the lucky benefiters, and it only takes about a week for me to start seeing gains. I did bloodwork one year before and after a 10 day trip to boulder, and it was drastic what happened. My own bodies EPO production went up around 35%, so concurrently I was also getting a lot more red blood cells. My HCT% also went over 50%, but I have a normal range of 46 to 49% at sea level, so what one would expect, small gains.
And I have always thought that training high for me, and sleeping low was the best formula. I think it got into the lexicon that sleeping high was somehow good for you, probably a spill over from the marketing of altitude tent makers. This guy in this study did find out that sleeping too high is not good for you, unless you actually live at that altitude and it is normal. But this is about training camps, not folks that live high all the time..
I guess that is why we get so many varied theories and stories about training high, it is all about the point of view of the writers, of which, we can not be sure what group they fall into for our comparisons..