I use both TR and Zwift and I went to climb ADZ (Zwifts Alpe d’Huez) in under an hour and just about managed. It was an all out effort for me and I couldn’t have gone harder. I then looked at my power curve…
My question - surely my 60min PR is now the most accurate representation of my current FTP?
Yes.
assuming you held steady power for the entire effort. For example if I went all out for ~60 minutes and the power curve for the Zwift workout looked like this:
My ftp is related to the first inflection point. Despite setting a 60 minute PR.
(Bad example, see Steve’s screenshot below)
So then you’d take 95% of the power number from 20min…at the first inflection? And set your training levels (Z2-4) with that number?
No. Poor example and misleading the way I wrote it.
Look at Steve’s reply ^
Thanks a much better example than mine.
Here is an long all-out effort and the power curve:
And I set season PRs for durations >20 minutes.
Like Steve’s example above, on my ride’s power curve you can see power drop-off between 45 minutes and 1 hour. Using my mouse I can see it occurs at 52 minutes. The power at 52 minutes is my FTP.
Because your all-out effort was 52minutes long?! What if you had gone all-out for the entire 60min, would your PD curve be different and show an “inflection point” at 60min?
If your TTE is 60 mins, yes. If it is 52 mins, you’d still see the drop off at 52 mins because after that you’ll be dying and the power drops off.
Actually trying to go past your TTE with an FTP effort gives you the best power curve to base this on.
If you do the whole thing at too low a power, your TTE will increase a lot, which also gives you a hint where FTP is. (If you’d want to go crazy with this, you could do long steady efforts at different power levels, and plot them against TTE. There should be a pretty clear change in gradient at FTP.)
There is a danger of this thread heading down a rabbit-hole with everyone’s different views of what the definition of FTP is.
I have always felt that setting your FTP is an approximation and setting it to the nearest 10W is good enough to determine efforts in interval sessions.
To answer the original post, it would be useful to know what you had as your FTP before and how it compares to the 60 min effort. If you are talking about a 5W difference does it matter? If it is substantial, the question is how did you determine your FTP previously?
That’s precisely the thing I don’t understand. Why does power go down dramatically if you slightly exceed your “TTE (FTP)” (meaning the TTE at power equal to FTP)? If FTP has the characteristic that small changes in power around FTP correspond to big changes in TTE (above FTP you fatigue much faster, under FTP much slower) then small changes in TTE should correspond to very small changes in corresponding power. (The derivative of the function TTE(P) for P close to FTP is big so the derivative of the inverse function, whose graph is precisely the PD curve, is small.)
Haha, I’m sorry about annoying everybody again with my not-understanding FTP 
(or rather my real problem is “TTE at FTP”, because I think it is not a robust quantity to track). I should keep silent and just work with my old school 1h power.
Nope, start with SST and see how long you can go. I’ll last way longer (perhaps double). Small ΔP, huge Δt. In other words, the derivative to the PD curve stays small even “to the right of” FTP.
I was assuming this. PD curve only makes sense when it’s filled with lots of all-out efforts in a fresh state.
Edit: To add something more constructive. It would be interesting to see the PD curve of somebody who has done a decent amount of testing at powers slightly below FTP. I’d suspect the “inflection point” would be nonexistent.
Why there is an inflection point in the PD curve at FTP (i.e. a small increase in time leads to way less power).
Ok, we are on the same page. The inflection point is just a modelling artifact (*). This was my understanding so far (I’ve read a couple of papers that describe PD curve models similar to the one used in WKO, e.g. Puchowicz et al.). Given this I found it funny people were trying to interpret something physiological from this inflection point.
Edit: (*) in combination with a lack of data points for durations corresponding to powers under (suspected) FTP.
Isn’t it just a log scale? Usually they tale it off with something that is basically linear in log t.
I agree that the power has a significance. I just think people over-interpret the time point (TTE) corresponding to FTP.
I’ve scrolled through the WKO document but I find the papers with actual formulas more interesting 
.
I’m sorry, I think we’re getting lost with not-so-productive stuff. Both you and I know how to guess and work with our FTP.
Because FTP is closely related to the point where blood lactate accumulates more rapidly. Physiologically, above FTP the working muscles can’t use all the lactate that is being produced anymore, and start offloading it into the bloodstream. That state can’t be kept up for very long. Below FTP this doesn’t happen. Look at a lactate curve to see the change in gradient. (Sorry I’m on my phone and can’t link a nice on easily.)
I’m sorry I expressed myself in a confusing way. I didn’t mean FTP not to be something physiological. My problem is the inflection point - there is no physiological inflection point, it is just an artifact of the model or a consequence of having a limited number of all-out tests.
I wouldn’t be too sure of that - there is a reason all advanced modelling has an inflection point there, and I doubt it’s because everybody introduces artifacts into their PD curve by only ever doing 2x20.
Anyway, as an experimental physicist, its sound like you volunteered yourself to do the series of “just above” and “just below” all-out tests 
Haha. Theoretical mathematicians don’t like to get their hands dirty .
Just look at the formulas. The lack of differentiability at TCPmax is just a consequence of the piecewise definition…
[Puchowicz, Baker, Clarke, OD PD model]
Damn I really shoud get back to my actual work, but I like this modelling stuff .
I’ve never understood why the WKO model shows a smooth downward deflection. versus the abrupt transition you see with models like this. Any idea?
My understanding is the inflection point is where you go past MLSS (maximal lactate steady state). Below MLSS, your body can clear lactate, above it accumulates.
