The fact is, both you and Alex have agreed there is no threshold or downwards infletion. at around 60 minutes, on the power duration curve. The curve, if looked at in real time, not log time, shows a continuous downwards curve, the longer the duration the lower the power and that decline in power is approximately the same rate from 20 minutes, through 60 minutes and well beyond. If there was a power threshold, this would not be the case.

Who are you and what have you contributed?

Both an all-out 50 min effort and an all-out 66 min effort would provide reasonable estimates of your FTP. That is because 1) the exercise intensity-duration relationship is quite flat in that region, and 2) FTP has never been defined as the power you can maintain for 60(.000000.....) min.

No, not really. First, the power duration relationship is quite flat in that region. Second, contrary to what you seem to be assuming, FTP has never been defined as 60 min power. 

The curve, if looked at in real time, not log time, shows a continuous downwards curve, the longer the duration the lower the power and that decline in power is approximately the same rate from 20 minutes, through 60 minutes and well beyond. If there was a power threshold, at approx 60 minutes this would not be the case.

He pointed out that there is no visible threshold in the PD curve. That's quite a revelation after years of everyone assuming that the flat spot (point of inflection) on the P.log(D) curve was a threshold.

It took me about five seconds to find 2 posts from AC that states the PD curve is "quite flat in that region"... from ST 2015...


From TTF

http://www.timetriallingforum.co.uk/...&comment=1637905

.. but the reality is that it keeps getting flatter and flatter up to a time well beyond 2 hours (in well trained cyclists with a high quality data population). So how can you say something is "quite flat" when it ~exponentially keeps getting flatter and flatter for a long time after ?

So I think that's a substantial contribution from Trev.

You are not thinking clearly.

Beyond a certain point, power declines *linearly* as a function of the *log* of time. (Runners know this as the Riegel formula or Riegel exponent.) That means that the slope is not constant as you claim, but is *ever-decreasing* as a function of *actual* time. It is because of this fact that the exercise intensity-duration relationship appears to settle at a plateau, as I showed in only the 7th post in this thread:

https://forum.slowtwitch.com/...ost=6633565#p6633565

Now if you assume that that apparent plateau is an absolute plateau, you have the critical power model. Of course, we all know that no power can be maintained indefinitely as assumed by the CP model, so the question is, at what point is the rate-of-change slow enough that you're willing to call that quasi-plateau an actual plateau?

One could argue about just how small the first derivative would need to be to fulfill that criteria, but from a physiological perspective, a power output that can be maintained for 30 to 60 or even 70 min represents a threshold for many phenomena, e.g., blood lactate, EMG activity, muscle oxygenation, ventilation, hormonal responses, etc.

What I said is true: the exercise intensity-duration relationship is quite flat out beyond the first few minutes of exercise. That is obvious in the nearly 200 curves shown in this post (note the X axis scaling):

https://forum.slowtwitch.com/...ost=6633565#p6633565

Indeed, for most people tripling the duration from 20 to 60 min only results in a 5% decrease in maximal sustainable power, i.e., the slopes is only 0.125%/min. Things only get flatter and flatter from there, at least up until the point that you "fall off the curve" due to, e.g., sleep deprivation, etc.

IOW, Trev has contributed nothing here but confusion, with you being case-study #1.

Trev wrote:

The interesting question is why physiological thresholds like lactate, don't seem to show on the power duration curve. What mechanism smoothes out the decline in power as duration increases rather than more sudden drops in power as physiological thresholds kick in?

I already answered that in my longish post earlier in this thread.

You have it bass-ackwards.

It's a smooth decline in power as duration increases not because physiological thresholds "kick in" as duration increases (such sustainable energy supply is already contributing at shorter durations) but rather because the rate at which non-sustainable limited-capacity metabolic energy supply sources are required to meet the power demand above threshold diminishes with duration.

It's a fixed amount of energy you have available to supplement your long duration sustainable threshold power supply. You can use it quickly for high power demand above that being met by sustainable energy supply, or more slowly for power a bit above threshold.

At a few minutes these non-sustainable sources might account for up to 1/3rd of the total energy supply. At 20 minutes it might be ~5% or so. At threshold their contribution is pretty small/negligible.

For some clues on why the P-D curve has the shape it does, have a read of this paper by Paul Gastin:
Energy System Interaction and Relative Contribution During Maximal Exercise


That's why inspecting the P-D curve for both short and longer durations is so useful as it helps to parse out each of the key physiological functional parameters, i.e. threshold power (or critical power if you use that model) due to sustainable aerobic metabolism, functional reserve capacity (or anaerobic capacity) which is primarily down to glycolysis and Pmax / peak power for very short duration power which is closely linked to the alactic PCr energy system.

As these physiological thresholds don't reflect in the power duration curve, should they be ignored and we just look at the power duration curve as a whole?

Isn't the decline from 20 min power to 60 min power more like approximately 7%?

1. Reverse the axes.

2. Start the power axis at zero.

3. Include data from shorter durations.

If you do that, your plot will look just like the ~200 I have previously posted, showing power to drop rapidly at first, then settling at a quasi-plateau.

Why you spend your time with these types is beyond me....

Why you spend your time with these types is beyond me....

Reminds me of the "There are four lights!" STNG scene with Picard and The Cardassians.

1. Reverse the axes.

2. Start the power axis at zero.

3. Include data from shorter durations.

If you do that, your plot will look just like the ~200 I have previously posted, showing power to drop rapidly at first, then settling at a quasi-plateau.

Indeed, because the last part is true (for both whole-body and isolated muscle mass exercise), the relationship can be modeled as if there is a perfect plateau that can be maintained forever. Monod and Scherrer called this the "critical power".

A number of us have realized and greatly appreciated long ago that he does it for many of our benefit and not necessarily for those like Trev that do not care to learn and are just trolling.

The point being that you can make any exponentially reducing curve look like a straight line or a threshold if you choose a broad enough y-axis.

That you chose to do that and it looks that way does not make it a true straight line or a true threshold

1. We are looking for something that looks like a threshold around 45-60 minutes, adding data points < 5 mins won't do anything to the shape of the chart in that region
2. Choosing a broader y axis is distorting the true picture further, there is nothing special about the number zero in this context. If you're trying to make it look like a threshold

Anyway, here it is, with the rider's 1 minute power added. Honestly, and I'm not trolling here, I don't see a threshold around 45-60 minutes. All I can see if you're looking for a threshold is some turnpoint between ~ 2 and 3.5 hours



Given the unfair, unpleasant and frankly gross accusations on this thread, along with the bullying that's gone on on previous pages, I think its time I went and spent some time on other things. This is getting a bit like sitting in a church trying to argue that god does not exist. I CBA, life is too short.