Significant overestimation of FTP

Hello there,
I believe my FTP estimate is far too high. Right XERT says it should be somewhere between 330-340W.
However, if I test myself on a long climb (30+ minutes) my avg. power is south of 300W.
Any idea what is going on?

Hi Matte,

Do you have an accurate Peak Power in your Xert profile. If your PP is underestimated, this may cause an overestimation of the TP.

Hi Scott,
Thanks for getting back to me.
PP is not underestimated, if anything, even a little overestimated.
Any other thoughts?

Is the breakthrough from 1 ride? You may want to try flaging the ride that resulted in the breakthrough, and see if that keeps the projected TP closer to where you feel it should be.

Hi Matte. Looking at your XPMC Progression and breathrough circles, I’d say things are looking very good. If you’re getting breatkhroughs, particularly if they occur near TP, then your TP is likely very precise. If you can’t hold 300W for 30 minutes, you may want to try it to confirm or perhaps look into why your have trouble at longer durations. (Most people dread longer duration efforts so I wouldn’t be too concerned. It’s probably just because you don’t want to suffer for 30 minutes).

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@scott: also Armando said, the estimate is based on a long series of smaller breakthroughs.
@Armando: Thanks for looking into the data. Most of my breakthroughs occur in vo2max efforts of 5-10 minutes. I would say I am pretty good at going deep for longer times and even enjoy the suffering. My avg HR was 170 on the last 30 minutes effort - don’t think I can squeeze out much more. Any other ideas?

There isn’t much difference between 10 and 30 in terms what systems are involved. If you can hit your 10 minute numbers, you should be able to hit your 30 minute numbers. Be sure you’re recovered and properly hydrated. If you’re overheating or tired, you’ll have trouble reaching your max.

I appreciate the confidence :wink:
I will give it another go tomorrow and report back.

OK, I tried it again. I was well rested, limited fatigue and properly hydrated. There is simply no way I am able to hold the numbers Xert suggests.
My HR is around 170, so I know there is not much more to give.
How exactly is my power curve estimate? Is this based on averages? Is there any way I can improve the estimate?

It appears that you can hit your 9 minute power recently ok. Which activity did you try again? The power curve is based on your signature. If you can hit your 9 minute power, then you should be able to hit your 30 minute power, although for some, it will be more painful. Your HR value has no meaning because everyone is different. If it’s elevated higher than it should be, there is likely some other unique limiter to your performance. I can’t say what that is but there really isn’t much difference between 9 minute and 30 minute power in terms of final wattage. You can estimate what those are using the power duration calculator.

I also find the FTP calculation to be too high & have raised this point in the past. My current FTP is 271W & is calculated from one of my local hills where I can maintain 300W for 7mins. However there is no way I can hold this wattage when riding on the flat. I do my local club 10 mile TTs & my power for these is between 225W - 245W. According to Xert I should be able to ride these at 280W but this is impossible for me. I don’t know whether the FTP calculation for a small climb is inaccurate or whether riding on the flat is completely different in terms of power usage? Or maybe I need to train better by riding long intervals?

I’ve found the same thing, Xert’s estimate of TP (FTP) gets jacked way too high based on rides where I have a “breakthrough” of 3 or 5 or 10 seconds above it’s calculated MPA in what is traditionally called the Anaerobic zone. How it decides a short anaerobic over-performance translates to a 5% jump in TP is a mystery they haven’t really been able, more likely willing, to explain in any detail.

So let me ask again: how does Xert generate its power duration curve numbers from mere snippets of data? It’s not just me that wants to know.

Before I “flagged” the most recent breakthrough ride Xert had my 2 hour power at what was TP just a week before, and 3 hour power less than 10 lower than that. There is no way, just no way that’s right.

Hi Ken, I had a look through your data and it looks quite good. Only thing I might ask: is your PP accurate? If your PP is underestimated by a good amount, this may underestimate HIE and overestimate of TP.

Your power duration curve is determined by your fitness signature…The parameters are determined by looking at the power that you generated, relative to MPA. This is why occasional maximal efforts are needed to establish (or validate) the parameters. Additionally, the relative intensity that generates a breakthrough has an influence on which parameters are updated following the breakthrough (i.e. a 5s breakthrough has a huge influence on PP, and very little influence on TP). This is why breakthroughs at various points along the PD curve will yield the most accurate fitness signature, as it’s more difficult to extract a TP from a short, bursty effort than a long, sustained one. You’ll likely notice more volatility in your signature early in the progression unt il you express your true maximal fitness. When the fitness signature is dialed in, it should be very difficult to achieve a BT. Hope this helps!

@adrian bennett if you can hold 300W for 7mins, even with periods of rest during the 7 mins (check… you’ll see you went below threshold over the effort) you absolutely have the metabolic fitness to sustain 271 a very long time. You may simply struggle to get all this power out on the flat like you do on a hill. The good thing is you have the metabolic fitness and simply need to work on your flat riding to match up what you can do on the hills with what you can do on the flats. This is similar to how those on TT bikes need additional training to be able to reach the same power they can sustain on their road bike. (Although In many cases, the discrepancy can be closed dramatically with a bit of motivation to withstand the suffering on a flat road. Put yourself in a race situation and you’ll see higher power than you expect on a flat. )

@ken milne If you only had 1 breakthrough out of many that exhibit this, then understanding why is going to take more data. The algorithm that picked up the signature on that activity is the exact same one that picked up all your other activity signatures. Something must be different in the ride’s data in comparison to all your other breakthrough activities. Curious what that is.

@matte 381W for about 9 minutes (it wasn’t even well paced) is 100% impossible for any athlete with a threshold power less than 300W. Like @ken, you have many breakthrough activities that exhibit consistent signature values, in line with what your training would imply except for a couple done recently. Is there a reason why they are different? You should investigate why your power data is so high.

@Armando Thanks for your response & sorry to highjack someone else’s thread. When you refer to additional training I guess you mean I need to do longer intervals i.e. a lot more 2 x 20 type workouts? I bought my TT bike at the start of this season so will spend the winter using it on the turbo.

It’s not so much the intensity but the muscle engagement. Practice intervals with more inertia (bigger gears) and faster cadence. These are the opposite of what you get on hills.

Scott, Armando: the question of my power meter accuracy keeps coming up. I do use 2 different ones, mainly, a Quarq Dzero on one bike and Assioma Duo pedals on two others. I had previously tested them against a Ptap GS (G3) hub on an indoor trainer at a set speed (20 mph) and all 3 agreed within 2 watts (taking into account the G3 will be lower by another 1.5% approx because of mechanical losses in the drive train.

Today I put the Assiomas on the Quarq crank and did a ride with some mixed intensities but no really high power, Those two PMs agreed within 2 watts for peak 5, 10, 30 and 60 second power, 5 watts for 20s power, and 4 watts for peak 2 and 3 min power, and within 2 watts for all durations longer than that up to 90 minutes. Normalized power (I know its not your thing) was within 1 watt for a 2 hour 20 min ride as was average power.

So I don’t think that either power differences between the two or absolute inaccuracies in both meters, since they confirm each other, account for the strange breakthrough rides where TP and 5 min power go up 5 or 6% in one ride ( to unobtainable levels). The last ride to blow up the fitness signature like that was 7/27, when I looked at it with the previous signature still operative the efforts over MPA were only 5, 2, 21 and 24 seconds long yet it increased my TP by about 15 watts, or 6%. That’s what I’m trying to understand, how such short “breakthroughs” can be indicative of such a large change in 40 to 60 minute power.

Hi Ken, you tested your power meters against an powertap on an indoor trainer. I am not a powermeter testing specialist, but I learn from the dcrainmaker blogs that it also depends on the test protocol that you use. Accuracy is different when doing sprints efforts versus constant speed driving. Differences can also occur when going outdoors (responses to different temperatures, driving on cobbles versus concrete, etc.). Key message: it is hard to compare figures that are obtained with different hardware in different situations / conditions.