I'll make this post short as I can so it doesn't get lost in my long dialogues. There is still nothing special inherently still about sub threshold. Other than it provides the biggest opportunity to impact load on the body in a way you can do regularly, but still be meaningful.
The accumulation and aggregate of what I do, is probably more than most training systems, but without the high tariff of the peaks and troughs and the really hard days or weeks, that then need the recovery I don't really need. Essentially that's it. You can get a lot out of it with just understanding that. There's a ton more I could write two books on let alone one, if you wanted to get into the weeds of finding the extra I worry about.
The "Norwegian Singles method" aspect the internet has coined it, has probably created a lot of the confusion of what it isn't, rather than what it is. I guess that just stuck as this is the original thread I happened to choose to post in.
I genuinely think still most of the picture , maybe 90%+ of the benefits of any training, is made up from the impact of load itself. The composition of training has very little effect in the grand scheme, especially if you still have headroom to get fitter without having reached dimishined returns. That's where training might be different for full time athletes or pros as the low hanging fruit starts to dry up and you need other ways to eek out some improvement.
Hopefully Coggan is reading this and I think I'm roughly quoting him and coming around to this way of thinking - put the work in and let the physiology sort out itself.
Re: MP stuff idea.
I've done 5+ sessions sweetspot in a week cycling, when coming back from winters off before settling back into a normal 3 sessions a week on the bike. Whether one could genuinely actually manage MP slightly broken for 20-30 a day as their base rather than what I do, who knows. As far as I know, nobody has tried it over a long period of time - which is what you need if you are assessing the impact of load. Hard2find wouldn't even try it and he's a human guinea pig, so that alone tells you it's probably not a good idea other than on paper. But if someone ever does for 6+ months, report back.