Originally Posted by
base2
Probabilities are by definition educated guessing.
Furthermore, a "20 minute FTP test" isn't 20 minutes.
Everything which isn't classical physics is probabilistic in nature. Calling it educated guessing is just silly.
In any case, it turns out you don't need to do some 20 minute FTP test on a trainer. Using a critical power and W' model, based on several shorter all out efforts both can be determined pretty accurately (Intervals.icu is a great tool which will do it automatically for you). Critical power highly correlates to FTP, typically a few % higher - adjust downwards to taste and presto.
The good thing about the model is that I can, say, predict the pacing strategy and performance for a 10 minute climb and it comes out very accurately, as well as pace long efforts if you have a bit of experience how it relates to what you can sustain for a long time.
As for my curves, my 10 minute maximum effort comes out as 4.38 W/kg, 24 minute maximum as 3.86 W/kg, 1hr 20m maximum as 3.4 W/kg. If I had an exactly hour long hill climb I'd try for something halfway between the two. Ironman / ultra endurance pace as 2.77 W/kg, bang on 200W. That's pretty typical.
If I had to regularly do 1hr at full gas on a trainer to determine my FTP, I would probably douse my bikes with gasoline, set them on fire, and quit cycling. Few researchers do that, too, because you have to find actually willing subjects nowadays 😉