Help estimating ftp from race power file

Hi all,
I had my FTP set at 292 Watts prior to doing a race yesterday. After reviewing the race power file, I think my FTP needs revising, but I'd really appreciate a little help from someone in the know regarding which method to use.

The race was a 40k race, after 3km I got off the front and soloed to the end of the race, putting out a hard consistent effort the whole way. The course was quite flat, with a few short downhill sections where I could freewheel for a small bit. I did no hard efforts other than when breaking away and the final sprint, both were short in duration, so shouldn't skew the figures too much.

I have only ever done a 20 minute test and taken 95% of average power before to estimate FTP before, but now having a hard 60 minute effort also available, I'd love to hear some advise on how I should calculate.

Here's what I have from the power file:
Best 20 min avg power - 307W
Best 20 min normalised power - 313W
Best 60 minute avg power - 297W
Best 60 minute normalised power - 304W

My question would be should I use the 20 min or 60 min values for estimating FTP, and should I use normalised or average power? If using normalised for 60 minutes, this would be a huge jump from 292W.
Strava estimates my FTP at 292W, and golden cheetah says CP-297W and FTP 291W.

I'd be very grateful for any advice on if and how I should make an adjustment to FTP.

Many thanks!

 

20 min's is too short a duration to make NP useful IMO. Looks like your VI for 60 min's is pretty low (1.02) so you could use either one really and it won't make any significant difference.

Considering error of PM's in general and the day-to-day variability of one's FTP, I'd just call it 300 and be done with it. I always round my FTP values off to the nearest 10 watts. It doesn't really "pay" to try and nail it down to the watt given the above.

 

Your FTP is 300w, I'd leave it at that.

 

Many thanks to both of you for your reply. I have it now set to 300W and all is well so far.
So from what I understand, if the VI is low, you can use either normalised or avg power, but if it is high, then neither would be a good use for estimating FTP as the effort would not have been steady enough. Would that be correct?

 

My figures for 'best' are the exact same as yours although i have been using my 'tested ' times. I did a hour test to compare and feel i was underpowered but was close enough to estimation with 285w. I frequently have nominated power of 10% higher than my 20 min best. But i also dont train on the flattest of lands= scotland

 

That's really interesting.

 

IIRC, the rule of thumb for using rides with VI's greater than 1.05 for FTP estimation is to use them with "caution". It's possible to have an "NP buster" for folks with good anaerobic capacity (AC).

There's a topic from the Wattage list that is appropriate here (7 deadly sins). I've always liked Alex's blog posts on the subject:
http://alex-cycle.blogspot.com/2008/05/the-seven-deadly-sins.html
and
http://alex-cycle.blogspot.com/2009/07/sins-of-sins-testing-ftp-2.html

 

You should never use normalized power for anything.

FTP is sort of a worthless measure. It varies a lot from day to day and it is a poor predictor of maximal power output for different durations.

But it is fair to say that you can put out 300w for an hour so you can use that as your FTP in whatever training plan you are using.

 

20 mins is pretty useless on its own. I'd use the 60 minute numbers, but since they're so close, I'd just peg it at 300 and be done with it. It really doesn't matter a bit if it's 297 or 304.

All training is prescribed in zones, anyway.

 

If the hour was a hard hour, then FTP is more likely to be closer to NP than AP irrespective of the ratio of NP to AP.

Some items:
http://alex-cycle.blogspot.com.au/2013/03/you-cant-touch-this-part-i.html
http://alex-cycle.blogspot.com.au/2013/03/you-cant-touch-this-part-ii.html
http://alex-cycle.blogspot.com.au/2013/06/you-cant-touch-this-part-iii.html

 

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