I am no histologist, but I gotta really wonder if the whole mitochondria thing is for real. How is that measured? We all love to repeat the "science" without bothering to actually research it. Are there actual peer-reviewed research papers about this? If so, I'd love to read a few. The "new" zone 2 bandwagon is probably (IMO) another way of not overtraining and getting active rest.
I remember that there was agreement about carbo loading, lighter bikes are better, stiffer bikes are better, stretching before exercise, eating more meat, high pressure tires....the list goes on.
(I still stick to the carbo loading because spaghetti is delicious)