I’m pretty sure the training the pros do at “zone 2” as instructed by ISM is right at and around LT1, are done as intervals as a part of an overall high volume program. That is the impression I got from his TTS interview.
One thing to also take notice from the article tables is the raw CHO numbers. The lightly trained athletes at 165 watts were using as much cho as the pros at 240 watts. Also pretty telling was that the CHO oxidation rate at 300 watts for the lightly trained athletes was nearly identical to the CHO oxidation rate of the pros at 396 watts. So a novice riding at medio is still burning a decent amount of carbs, further stimulating those glycolytic pathways.
Improving fatmax comes through a combination of factors. I had long suspected that being in a calorie deficit has more benefits to an endurance athlete than just losing weight, as it also puts the body in to a system where fats are utilized more than CHO, when compared to equal energy balance or positive energy balance. This is also in the article as well, and was bringing back memories of general biochem from 25 years ago. CHO ingestion/utilization is going to have the major impact on fat oxidation. Intensities where CHO is necessary will blunt fat oxidation during exercise, and ideally longer distance athletes would favor fat over CHO. Lactate is also a signaling molecule, and higher lactate levels shut down beta oxidation and downregulate the other steps necessary for fat oxidation.
I think the influence on medio work, say compared to just doing a high volume is minimal. And people always seem to forget that you don’t need to do 20 hours to stimulate adaptions, you just need to do more work than before. If one is not very fit, that’s usually the first thing they should be attempting, how to fit in the time. The major contributing factors to success in endurance sport is volume and consistency. There are lots of threads on this site talking about failing workouts, which can lead to a huge negative feedback loop of repeated failed workouts if one isn’t careful and ego gets in the way.
I also think the benefits of training more at a lower intensity has had some initial unintended consequences, as people used to do it for necessity, but in the end, there definitely seems to be a key benefit in being able to do a large amount of work without overloading on stress as the Norwegians have been shifting to less zone 2 and more zone 1 for their endurance work.