While the majority of analysis in Crickles is based on heart rate data, we do also do some proper analysis of power data. This is mainly to inform various Crickles models but FTP curves are also shown. I hesitate to include much more in the Navigator about power because people’s strength of feelings about their FTP tends to exceed the quality of the science. Books and websites that advise on FTP estimation offer a number of protocols that virtually all boil down to one of two methods:

  1. Ride as hard as you can for an hour. Your average power is then your FTP. This method is faultless. However, it’s far less commonly advocated than…
  2. Ride for a shorter period and multiply your average power by a factor to adjust for the difference.

Typically the shorter period is 20 minutes and the multiplication factor is 95%. Method 2 is so much more common than method 1 that we might say that the de facto definition of FTP is your best 20 minute power multiplied by 0.95.

There must be an evidential basis for the use of 0.95 somewhere but I can’t find it. Whenever I look at actual data I come up with a different number. Again just recently, I’ve taken a sample of Crickles data using the activities over the year-long period 2020 Q2 through to 2021 Q1 of 276 athletes who regularly cycle (on the road or on a trainer or both). On average, these athletes had 176 qualifying rides during the year. For each of the four quarters (2020Q2, 2020Q3, 2020Q4, 2021Q1) separately, I looked at the highest 20 minute power and the highest 60 minute power that each athlete sustained. The ratio of the best 60 minute power to the best 20 minute power gives a number that can justifiably be used to scale a 20 minute all-out effort into an estimate of power for an effort over an hour. For each athlete, I averaged the ratio over the four quarters . Thus I have an estimate of what the weighting factor should be from each of 276 athletes.

It is not 95%. The average across all athletes is instead 88%. That means that an athlete who can push out 270W over 20 minutes with an all-out effort might expect to manage 238W over one hour; the 257W that a 95% weighting would imply does not correspond to what we see in real life. By the end of an hour 19W will seem like quite a difference.

The ratio is reasonably consistent across athletes with the majority of athletes having values between +/- 3% of the 88% average (i.e. in the range 85% to 91%). Of the 276 athletes, only three (1%) had values of 95% or more. The weighting is not materially correlated with either age or FTP. It may legitimately be thought that hard 60 minutes efforts are rarer than hard 20 minute efforts but taking the ratio of the highest 60 minute power to the highest 20 minute power for each athlete over the whole year rather than quarterly does not change the result.

I’m curious about what data the ubiquitous 95% figure is based on. Whatever it is, if you’re reading this the Crickles data is likely to be more representative for you.

5 comments

  1. Ian, I wonder whether the issue here is that few riders give it their all for 60 mins, unless they’re competing in a 60min TT? I rode up Alpe de Zwift the other day with the objective of getting under the hour mark, which I did – just! 59 mins 17 secs, which is conveniently close to an hour – my average power over the climb was 237W – and it was a max effort. My FTP calculated by Zwift using (I believe) the 95% method was 241W. So, pretty close… I can’t recall another time that I went all out for 60 mins – so the data you’re using may have shortcomings?

  2. Hi Paul, That’s a sensible question but nonetheless the stats are deep enough to give me confidence that the 88% number is about right. I’ll send you info separately, since it concerns your data, showing why your data point is less surprising than it seems and doesn’t change the overall picture. If we look at 65,000 activities and are seeing only three people in a the course of a year hitting 95% of their 20 minute power over an hour that’s compelling. There are other factors that I haven’t covered in this short piece – such as the shape of the power curve – that also support the conclusion.

  3. Ian,
    A few points about FTP.

    1. Over the years I’ve never considered I could ride for an hour at my FTP. No matter how it was calculated (Usually from the 20 min method). I used to do 10 mile TTs about 35+ years ago. I hated 25 mile TTs and seldom did them.

    2. Some time ago I was talking to two friends who were coaches, they considered FTP to be the power one could maintain for a “long time”. This may be more or less than an hour. The actual time you could maintain it for was dependent on the individual and the type of cycling they were training for.

    3. I understood that the purpose of FTP was to establish power training zones. As we can’t all have blood tests to determine lactate levels then the FTP test was established as a proxy. The hope was that it would enable power training zones to be set which were close enough to those established with blood tests so that people could train with a power meter. Whether it is a good proxy or not I don’t know. I guess there should be some sort of study out there. As the aim is to establish training zones it does seem odd that “1 hour” becomes a magic number and not 55 minutes?

    4. FTP will change.

    The important aspect, I guess, is that the power training zones are reasonably accurate for the purpose we wish to use them. How they are established is less important. However if the test is too hard it won’t be used. It needs to be reasonably accessible and reasonably accurate for a good proportion of the population wishing to use it. I’ve no idea if a 20min FTP test does this.

    I guess I share your misgivings about FTP and the elevated status it has been given.

    Nick

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