Relationship between normalized power and ftp?

Discussion in 'Power Training' started by Dave Kalbach, Apr 1, 2016.

  1. Dave Kalbach

    Dave Kalbach New Member

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    I have been reading Allen and Coggan's book "Training and Racing with a Power Meter"

    While nearly finished reading, and having most of the testing done I ran in to a question today. I'm a new rider so please don't laugh at my numbers...

    I believe my FTP to be 165 (based on the 95% of 20 minute TT criteria)

    My historical Power data, along with current data seem to support this number as being accurate. Then today I rode a pretty good effort for about an hour and a half. However, I was doing intervals that worked out to about 30 minutes each (3 intervals - but lost the data to one due to setup) None the less, the hour I recorded gave me a Normalized Power of 165W.

    If normalized power takes into consideration uphill, downhill, coasting, etc., and I have an exact hour of data (64 minutes actually) then it should be a true FTP. I'm not looking to prove my FTP, I can test for that. I just think this seems like a fairy simple way to VERIFY my FTP. Provided of course you have a 1 hour segment to look at.

    Can anyone confirm this?
     


  2. Weatherby

    Weatherby Well-Known Member

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    From my experience NP can be close to your FTP if you ride in a steady state fashion. I think NP is better than average power for my purposes because of the road conditions and traffic make it difficult to do a 20 minute effort let alone a clean 1 hour test unless it is on a TT with relatively clear roads.

    It is pretty easy to trick the NP algorithms by periodically doing a hard 10 second jump every once in a while or by strategically coasting.

    I down load my data into three different programs and the FTP estimation varies by 6-8 watts, which is close enough for my purposes.
     
  3. Dave Kalbach

    Dave Kalbach New Member

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    Which programs? Hoping there is a "free" one

    I'm using Garmin Connect which does not calculate FTP. I'd certainly look to upload my data into one that did. Just to Validate my numbers and beliefs.
     
  4. Nigel Doyle

    Nigel Doyle Member

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    Personally I do my FTP tests indoors on my Trainer and in conjunction with Trainerroad using one of their testing workouts. If I happen to do an outside TT then this in most cases confirms my FTP is about right. Doing the test on a trainer gives much more consistent power output. E.g. my FTP tested indoors is 306. Yesterday I did a TT and my time for the 24km was just over 40 minutes. Avg power was 293. Normalized power was 298.

    What I find is my FTP is higher than what I can actually sustain for an hour but this figure is about right for power based workouts where interval power targets are a percentage of FTP.
     
  5. Dave Kalbach

    Dave Kalbach New Member

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    I have done my Power Tests indoors as well. Just looking to verify as you have done with your TT
     
  6. An old Guy

    An old Guy Member

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    A large number of people have shown that there is no science behind normalized power or FTP. Coggan was asked to come up with a gimmick to promote trainingpeaks.com.

    Average power is a better measure. I usually set up my training to do a certain amount of work (joules).
     
  7. RapDaddyo

    RapDaddyo Active Member

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    The answer to your question is yes, normalized power (NP) for a 60-minute segment of a variable power ride can be used to verify your FTP. To understand why, you need to understand what the NP computation does and why. Normalized power, like average power (AP), is a weighted average of watts formula. But, whereas AP weights watts by duration, NP weights watts to the 4th power by duration. The effect of this is to give a greater weight to the higher watts numbers than the linear arithmetic relationship. So, why exponential weighting and why the 4th power as opposed to some other power? The answer lies in the relationship between stress and power as a rider increases intensity (power). Stress is measured by blood lactate, which increases as a rider increases intensity and can be measured. A study of this relationship for many riders reveals an exponential curve to the 4th power (actually, 3.9 rounded to 4 for simplicity). So, the science behind normalized power is the observed relationship between stress and power for a large sample of riders.

    A way to think about normalized power is this. Let's say you go out and ride for an hour with repeats of 5min at 140W and 5min at 180W. What 60min constant power effort is the stress equivalent to? The average power is 160W, which weights 140W and 180W equally since the cumulative duration of each is the same. The NP computation weights watts at the 4th power, which gives greater weight to the 180W efforts even though each has the same cumulative duration. The NP for this ride is 164W. In my view, NP is a much better approximation of the total stress of the ride than AP.
     
    dhk2 likes this.
  8. kcj

    kcj New Member

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  9. dkrenik

    dkrenik Member

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    Good advice here (except for AOG - ignore the troll).

    Some folks say that NP is useful for excursion of 20 min's or more. I prefer to use 30 min's and more myself. when using it for FTP analysis one should also take into account the Variability Index (VI). If it's much more than 1.05 the effort probably isn't going to be useful for FTP analysis. Some folks are blessed with more AC and that can lead to an overestimation (FTP buster) of FTP.
     
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