As I enjoy thinking about this kind of thing, I’ll recount my understanding, but don’t take my word for it (I don’t work for the company after all, this is just my understanding based on Markus answer he gave in this thread: How are the training zones used during plan generation?
I suppose that’s the difference. The mapping of ‘threshold’ or ‘vo2max’ is, in my understanding, a labeling convention and not used when generating the workouts. The ML model determines the optimal pace/power for time within constraints (sports being trained, availability per week, date of event, type of event, etc.) and then maps this onto workouts which are given the label ‘threshold’ or ‘vo2max’.
Put another way, the watts to produce for a certain duration comes first, and then sliced into a 14-day microcycle where individual workouts are created, and within that 2 week period if you need X minutes at A watts, you get a suitable number of workouts where you, if done with 100% optimal adherence, hold the A watts for X minutes over the course of that microcycle. When creating the individual workouts it groups ‘like’ wattages together into various labeled buckets (endurance, tempo, vo2max, anaerobic, etc.) which show up on your training calendar. This explains, in part, how you might have a ‘threshold’ workout with one 9 minute threshold interval and 30 minutes of endurance.
This imprecision sounds a bit weird (what are the cutoffs between endurance/temp, is it halfway through? Ceiling/floor functions? Rounded up/down? etc.), and then I recalled Xert has the magic buckets which let you overshoot intensity for a given ‘bucket’ and it compensates by reducing the duration of the interval, and that’s a pretty mathematically driven organization (but they don’t do run training so … not for me), and TR does something similar with their ‘daily workout’ suggestions (but not season planning, at least not according to the most recent episode with CEO Nate Pearson).
None of that explains how Endurance Power, Functional Threshold Power or Critical Power is calculated. Though from my understanding, FTP has no physiology-based definition (assuming you take Andy Coggan’s word on how the idea behind FTP was to not require learning the physiology, which he elaborates on in an episode of the Inside Exercise podcast https://youtu.be/-6DhfMJH84E?t=1760 (timestamp jumps straight to this discussion). As “evidence” on the non-standardization of FTP, TrainerRoad has redefined FTP in their platform to a ‘level 3 threshold’ (whatever that is), but whatever it is was not in “Training and Racing with a Power Meter”.
I hope Markus can answer your questions, I am also interested in the answers.