You do understand that that is just a schematic diagram that I drew to illustrate the point, don't you? (Actually, apparently not.)

I think this statement illustrates the crux of your confusion regarding 'threshold'. Just about everyone understands what 'threshold' feels like and knows what it's like to ride at threshold. Increase the power much above threshold and you won't be able to sustain it.

As a thought experiment, imagine if that curve that Dr Coggan drew was perfectly flat. There would be no kinks, tails or elbows but the result would be a clear threshold in terms of sustainable power. A threshold is not associated with a drop off in power at a particular duration. A flat power curve is an illustration of a 'threshold' in power.

The point is you put up a graph which does not show what you claim it does. Your so called small increase in FTP is approximately 25 watts, 9%, that is not small.

My comments are about the graph, it is of no consequence that you now claim you just made it up. One must quesstion how many graphs or charts you post which you just made up.

Are you now claiming you drew a diagram which is inaccurate?

It shows exactly what is stated on the figure. Any change in Y is accompanied by a much larger change in X at the initial Y.

As long as the slope of the line is shallower than 45 deg, that will be true regardless of how much or how little Y actually changes.

It is me who is pointing out that if there is a power threshold it should show up on the power duration curve as a flat area. It is the lack of a clear flat threshold showing on the curve which is one reason I question FTP.

Looks pretty flat to me. Why were you talking about tailing off, elbows and kinks if all you were looking for was less slope to the curve? I think you need to ride more and argue less.

If you think a continuous downwards curve like that illustration is flat, you are confused.
I mentioned tailing off, elbows and kinks because others have referred to them, it's me who argues they don't exist on the curve.

If I look at my CP curve a 5% increase in power results in a 50% decrease in TTE. That feels very much like a threshold I shouldn't go over if I'm trying to complete a 1 hr effort.

Trev is a troll, he has many threads on this subject.

Trev, you really must try harder not to look like a fool.

Squeeze those two illustrative PD lines closer together, so that for example the difference in power at the same point in the illustration was say just a handful of watts (plausible enough for you?). Then draw the horizontal line again to see the impact on TTE. A 1% change in power in that region of the curve will still result in ~10% change (give or take) in TTE at the original power.

Even though Andy's diagram was for illustrative purposes, you suggested 25W was not realistic/plausible.

I personally have two PD curves that are 78W different at 60-minutes.

At the same absolute power at which the lower PD curve is at 60-min, the upper PD curve is at 3.5 hours.

---

http://www.cyclecoach.com
http://www.aerocoach.com.au

The illustration shows that if you improve TTE / time to fatigue you also improve power around the 60 minute mark. So if you look at my original post in this thread, the diagram confirms what I was saying. If you increase TTE from say, 40 minutes to 70 minutes, your power at 40 minutes will have also increased.

I pointed out that the approx 25 watt increase, an approx 9% increase in power is not small so the illustration is misleading. No one disputes that an increase in power causes a shorter time to fatigue, my point is that you can increase power almost anywhere on the power duration curve and get the same sort of reduction in duration and that there is nothing special about approximately 60 minutes.

Strictly speaking, this is not true. At short durations, the change in Y is greater than the change in X.

Yes, agreed, I should have made it more clear, instead of using the word ' almost'. Out of interest what durations would you class as ' short ' ? Up to 10 minutes? 5 minutes? Or even shorter?

It was a statement of fact, not an opinion:

Thanks for posting the chart. On my small iPad it isn't easy to see exactly the time line. I assume that is a chart using actual data and not just an illustration.

Would you agree that chart shows short durations, in the context of this discussion, would be anything under approximately 3 minutes?

We can make similar statements about other durations, though. If I add 5% to my 20 minute power, I see an approx 50% decrease in TTE. If I add 5% to my 100 minute power, it gives an approx 50% decrease in TTE. So 60 minutes doesn't differ from many other points on the PD curve in this respect.

Yes, log-normalization of the data (i.e., using percentages) is one way dealing with the non-linear nature of the exercise intensity-duration relationship, e.g.:

https://www.ncbi.nlm.nih.gov/m/pubmed/18379223/

https://www.ncbi.nlm.nih.gov/m/pubmed/15809572/

OK. My snarky comment would be: so what? For better or worse most people have become accustomed to using roughly 60 min (FTP). Seems to work well for most people for tracking workload, setting training bands, general communications etc. I suppose one could define some other time period for standardized power measurements but at this time what would be the point?

First of all, I'm not arguing against the idea of using 60 minute power as a reference for setting training zones. That is absolutely fine as a concept, and Olbrecht, for example, put forward a similar idea many years ago. What I'm arguing against is the claim that there is some sort of "threshold", a feature in the power duration curve, that is unique to the region around 60 minutes. When we press the people making this claim for a sufficiently rigorous definition to enable the claim to be tested, by seeing if the region around 60 minutes satisfies their definition, while other regions do not, they will not provide a sufficiently rigorous definition to allow that. The definition you gave, of a 5% increase in power giving rise to a 50% reduction in TTE, is a sufficiently rigorous definition, but the 60 minute region is not unique in having that characteristic.

Whether or not its unique there is definitely a threshold in power in the 40-70 min range where the power is defined as FTP. If you used some other time period in that vicinity, e.g. 20 min there is also a threshold that is very close to FTP.

It's not clear why it needs to be unique or precisely pinned down. FTP is always somewhat 'fuzzy' depending on training load, fatigue and a host of other factors. I think of it more as a band of power rather than a precise number.

But you're talking there about two different "threshold" values, one for the ~60 minute region, and one for the ~20 minute region. Basically, all you're saying is that for a given duration, there is a max power you can sustain for that duration, and if you try to exceed that power, you'll reach exhaustion sooner. That is totally true, nobody would disagree with that.

What isn't clear to me is why we can't just talk about x minute power, and what value is added to training by describing it as "FTP" and insisting that there is something unique about the 60 minute region that differentiates the shape of the power duration curve in that region from all other regions. That isn't your claim, so that isn't a criticism of anything you said.

I think you could possibly make that argument where the power curve is essentially flat or linear with a small slope. That's not the case for short durations (i.e. under 20 min). Going beyond 60 min isn't particularly useful for most people as they don't very often do max efforts at those durations so 60 min seems a good number to settle on.

I don't see any advantage in everyone using a different x for defining their threshold. FTP seems a useful concept for many and simplifies communications. Despite some feeling FTP is dead it seems fairly ubiquitous (embedded in millions of Garmins) and I'm not sure your concerns with the definition resonate with very many riders. At some point inertia makes it difficult to change systems even if they aren't perfect. Once you've got everyone weaned off FTP you can start working on the Imperial measurement system :)

Again, I'm not arguing that. As I said, picking a duration and using power for that duration as a reference is fine. We could call it something like, say, "60 minute power", maybe call it P60 if we want to shorten it to 3 characters. What does FTP add that isn't provided by using P60?

Everyone (almost) has adopted and understands FTP. There's no value in changing now. What would be the point?

Until not that long ago (basically when WKO4 shipped), most people who had adopted FTP were regarding it as interchangeable with 60 minute power or 25 mile / 40km TT power. Threads like this one didn't exist at that time, as there was no need for discussion of these issues when FTP essentially meant the same thing as P60 (60 minute power was described as the best way to estimate FTP).

What changed with WKO4 shipping is that FTP was no longer equivalent to 60 minute power or 25 mile / 40km TT power. Now it has a floating duration, it might be your 40 minute power one day, then you feed it another file and now it's your 70 minute power. To be able to choose this point, it is claimed that there is a characteristic in the power duration curve that is unique to where FTP is located. Some people, and I am one of them, dispute that such a point exists in that region, with a characteristic that is unique to that region and doesn't exist outside that region. When challenged to provide a definition that would allow their claim to be tested, they will not provide one.

Re your question of what would be the point of using 60 minute power or 25 mile / 40km TT power as a metric instead of the WKO4 concept of a floating pair of numbers, (duration, power) - for me, it would better match my actual performance, as I don't really want to have to wonder whether xW for y mins represents better or worse performance than aW for b mins, and I've seen my WKO4 mFTP move significantly in the opposite direction to my actual performance, even when the duration it has picked hasn't changed significantly.

When you look at the paper that was published fairly recently that appears to support the concept of FTP, it's actually using FTP as a synonym for 60 minute power, not the floating (duration, power) concept of WKO4. So there is an example of a group that is still in fact using P60 rather than FTP, even though they described P60 as FTP.