2

Often it is argued that an 8 or a 20 minute effort can be sufficient to estimate Functional Threshhold Power (FTP), an indicator of how many watts a rider can put out over the course of an hour (or 40 minutes, depending on who you ask).

For a 20 minute effort, it is often argued that a 5% reduction over the 20 minute wattage gives an accurate estimate of the maximum wattage for the 40-60 minute effort.

For the 8 minute effort, an additional 5% (for a total of 10%) is taken off the total wattage over 8 minutes.

My question is as follows: does the reverse also hold? Suppose I do an 80 minute test, or a 160 minute test, will a respective 5 or 10% increase in the wattage over that period be my FTP?

Improve this question
3
  • Probably pretty close, but FTP is an estimate, and you're estimating an estimate, which will have a margin of error. You'd have a hard time putting out your FTP for such long times - you want a quiet and non-stop, flat road for perhaps 40 km. That's hard to find, hence the shorter heuristics.
    – Criggie ♦
    Commented Jul 11, 2017 at 0:02
  • 1
    I wouldn't put much faith in any of those numbers.
    – Daniel R Hicks
    Commented Jul 11, 2017 at 3:33
  • Worth noting that the 8min protocol isn't simply 90% of 8min wattage, but 90% of the average of 2 8min efforts in the same session. Additionally, you'll have a tough time convincing someone to do a 80 or 160min test to estimate the power they can hold for 40-60min. Better to just do a 60min test and forget the "estimation" portion.
    – Ealhmund
    Commented Jan 14, 2020 at 20:50

1 Answer 1

Reset to default
5

As a rough rule of thumb, those ratios are approximately right but there is quite a bit of individual variation and there will be more individual variation in the mean maximal power to FTP ratio at shorter durations than at longer ones.

If we consider a mean maximal power curve, a plot of the maximal power one is capable of sustaining plotted against duration, it is generally pretty flat from 8 minutes out to many hours. It's not of course totally flat and there are various individual factors that influence the shape of the curve. The slope is greater at the shorter duration, and it has more individual variability there.

This example curve taken from Jack Mott's website shows (note time is on a log axis):

enter image description here

Now while this is the general shape of a MMP curve, there is individual variability and I chose this image as it gives some clues as to why, namely the contribution of the various metabolic energy systems that supply the energy varies depending upon the duration of a maximal effort, and also upon the unique physiological characteristics of the individual.

So while long duration efforts are dominantly fuelled by aerobic metabolism, during shorter maximal efforts there is a greater contribution to the energy demand by anaerobic metabolism, and anaerobic capacity is highly individually variable.

As a result, the ratio of short duration power capability to FTP can vary quite a bit between individuals, while the ratio of long duration power capability to FTP will be less variable.

Improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.