Given the widespread misunderstanding of my post, I must take the blame for being a very poor communicator !!
I appreciate folks trying to explain to other folks what I meant, but unfortunately it just muddied the waters because it’s not at all what I meant.
I’ll try one last time to be crystal clear
My main point was simply that the zone you’re in when performing a structured interval workout is determined primarily by the duration of the work intervals. I think most of us use Coggan’s durations of < 30 seconds for Neuromuscular, 30 seconds to 3 minutes for Anaerobic, 3 minutes to 8 minutes for VO2max and 8+ minutes for Threshold.
Hopefully we all agree that different energy systems (Phosphagen, Anaerobic Glycolysis & Aerobic Glycolysis) are best trained at different durations. So, for example, hitting a 1 minute interval workout hard is going to primarily train your Anaerobic Glycolysis system, etc.
Naturally, this assumes a best effort - barely pushing the pedals around for a 2 minute interval is obviously not a good anaerobic interval!
I’ve used this approach since Mar 2018, and it’s worked extremely well, and I think it’s probably because I’m always pushing myself to the limit - e.g. if I did a 3 x 4 x 1-min. workout at 385 watts, then the next time I’ll do it at 388 watts, for example. I don’t wait for an FTP test to do this, I just make it harder in some way every time if possible. I use the TR Workout Creator a lot to create these custom workouts - I just use two VO2max workouts and three Anaerobic workouts (since I follow a polarized approach, I don’t do sweet spot / threshold work).
I’m not proposing this for most people For one thing, it requires some detailed tracking (I use a spreadsheet), and for convenience, it works best if you use a relatively small set of workout formats as I mention above, but we really don’t need that much variety to stimulate these energy systems - a couple for each energy system is fine.
And as others have noted, it doesn’t work for sub-maximal efforts, so anything below Threshold is a bad fit. Fortunately, Stephen Seiler’s polarized training approach works extremely well with this approach.
If you want to test your FTP frequently, that’s fine, but for me, I just prefer to keep ratcheting up the effort for the various energy systems.
The secondary point that some have fixated on is that this approach also allows for individualization for different types of power profiles, but I agree that point is minor, and most of us are probably in the middle of the bell curve here.
Sorry for all the confusion - for most people, just pick a TR plan and follow it !!