FTP test and W' bal

[Bart Coddens]

Hi All,

In the attached file you can see a screenshot of the FTP test I just did.

When I look at the W' balance I can see that I did not reach bottom.

Does this mean I underestimated my current FTP ?

I started at 255 Watts, in the left corner you can see the interval and this proves my guessing was about right.

Best Regards,

Bart

[Mark Liversedge]

1.5 kJ left is pretty close to exhaustion.

How did you feel at the end, it looks like a nasty ride :)

Mark

[Bart Coddens]

Quite Exhausted :)

[Nathan Townsend]

There are multiple reasons why W'bal may not coincide closely with 0 kJ at exhaustion.  One of those is of course CP + W' estimation error.  In general, when the effort duration is longer than about 60-90s, errors in W'bal at exhaustion have more to do with the CP estimate.  When the effort is short, then error in W' makes a bigger difference (this should be pretty simple to understand purely from a mathematical perspective).

If CP is underestimated, then what tends to happen is that W'bal drops negative during HIIT because you're telling the model that you are less fit than what you really are ie: you can actually produce more power and expend more energy than what the model "thinks".  Converse applys for overestimation of CP.  So for example, it might be that your CP is slightly overestimated in this case.

Another factor is that performance is always variable anyway. So maybe you're a little bit more fatigued on the day you do some maximal effort intermittent task as compared to the day or days when you did efforts to model CP.

Lastly, a problem which is common to all scenarios is that neither the integral model or the differential model is perfect. At present the models are a bit too simplistic and so they're not robust enough over a braod range of situations ranging from say short shart crit race style efforts on one end of the spectrum to longer sustained efforts but with long recovery between efforts (eg: a road race circuit with one big hill.  Everyone recovers on the flat section in between the hill, then pushes hard on the hill each lap which creates the selection).

[Neil Pugh]

Funny looking test.

[Armando Mastracci]

Bart, 

It looks like your test was done on a smart trainer.  Power is never this even when you are using something like a PowerTap or SRM.

We’re actually in the middle of developing a “powermatch” feature for our Xert Mobile.  There can be a considerable difference between the power coming from the trainer and the power coming from a power meter, even when the trainer is calibrated.

You should test from the same power meter and one with robust, consistent results.  A 10-20W discrepancy between different units when performing workouts above FTP to exhaustion will make a *huge* difference in determining how much W’ gets exhausted.  If you have access to software that can do powermatching with your trainer, opt to use that every time for best results.

Armando 

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[Bart Coddens]

Hi Armando,

Yes the test was done on a kickr with perfpro where my Garmin Vectors were powermatching the wahoo kickr.

Kind Regards,

Bart