Ah you see Jan, the guy was replying to you who said that stuff was improving biomechanics, which is probably partly true, but hugely, overrated. As was pointed out, 3 min reps aren't slow. You can run regular 10k pace if you do 90s repeats and you can run subthreshold even down to 45s at very high speeds, if you know how go control it (something that worryingly, 3-4 pages back you didn't see to understand, whatsoever).
Of course, anything can increase load, however you track or manage it. That much is clear. But the point being, the disproportionate amount of this kind of work you have to do, to make up for what you are missing out of further down the chain with having to make Subthreshold compromises, probably doesn't make up for it, when you enter in recovery cost.
The book to me was very useful. Especially the part on diminished returns. Once you reach that stage, of course you then have no choice but to add intensity and the specificity of the load does become important. The chart on page 125 lays this out very well. They'll be a point in which just spamming load isn't the key. But this is much further down the line than most of us will ever get.
But it comes down to this. In my mind, whilst you are getting what are essentially easy gains, from playing around with Subthreshold 3 times a week, everything else comes secondary and the whole focus should be making sure you get 3 workouts a week in, at the absolute priority of everything else.
Once you have exhausted that, as Canova put it, "then you come to me for rocket science teaining". When you have plateaued for good as per the graph on page 125, this is when Canova can help you. But i can't imagine myself ever getting to the right hand side of that graph and my progress is still relatively linear to the extra load i can do, well over a year into NSM. It's just very slow, but over years, ends up quite big.
(This also was in the tapering section and also makes sense about why hobby jogging tapering should be far shorter than an olympic marathoner, as a quick aside)
The question is, when is enough Subthreshold spamming enough? When is this eternal base phase finished? when do you reach this plateau of easy gains from below opposed to needing some real, specific focus? The problem with a lot of hobby jogging coaching I have had, is this seems to be something crazy, like after 6-8 weeks coach says "good winter, time for some intensity". Whereas the low volume we are running in comparison to elite runners, we are not even looking at months, but actually years before we get to this point.
We can all debate and argue the theory all we want. But what we can't hide from is what is happening to (and this is a conservative guess) at least 80% of all the people who have reported trying NSM over an extended period of time, that have improved and seemingly continue to improve.
Sirpoc seems to have found a way of reaching the max on running and still managing to tease some improvements out (he looks in lifetime shape?) by using cycling, with just making that Subthreshold, and still not hitting the big red panic button marked intensity. He has probably gone far beyond his ability in two different sports, training the same way, that I have no doubt he would have got nowhere near had he listened to some of the advice here, or continued to struggle in the same way he laid out in the book, that I'm sure resonates with an significantly large proportion of us.