FTP estimation with 20 minute test
 

I finally got to test my best 20 minute average power today to estimate my FTP. However, I found another FTP estimation method online other than the one I already knew, which was 95% of 20 min average power.

The other method is the following. Quoting source from power2max website https://www.power2max.com/northameri...culate-my-ftp/

Estimating from short duration tests

If you have a recent 5 and 20-minute best effort, you can estimate your FTP. Some sources suggest that simply taking 95% of your 20 minute value offers a reasonable estimate. I have found that this significantly over-estimates the FTP in most circumstances and offer this alternative method:

Identify the % drop off from your 5 to 20 minute test
e.g. if 5 minute = 400W & 20minute = 300W, the drop is 100W or in % terms, 100/400 = 25%.

2. Multiply this % by 0.75 = 18.75%

3. Take this % off the athlete’s 20 minute value to get a good estimate of FTP.

So, for this athlete, we would multiply his 20 min test of 300W by 18.75% = 56W and subtract this from 300W to get a good estimate of FTP, in this case, 244W.

This method takes into account the very real differences in each athlete’s power-duration or ‘fatigue’ curve, a concept we’ll explore in future articles.


I'm a recreational cyclist starting to learn about power training trying to improve. In your experiences, which method is more accurate? Intuitively, the second method makes more sense to me as it attempts to take into consideration the "fatigue profile" of an individual athlete rather than assuming a flat 5% decline for everybody. I'm wondering if I should test my 5 min max power as well. I've looked at a lot of numbers for the past couple of weeks from Strava Premium power curve, WKO4 free trial, TrainingPeaks and Golden Cheetah. I'm starting to think the only way to really get my true FTP is to actually do a 60 minute max power run which would be painful to do.

What are you planning to do with the FTP number you get? If it's just for setting your training zones either method will get you in the ballpark. After that you can adjust the power for interval efforts based on how easy or difficult it is to complete a given workout. If the workout is too easy, raise your target.

Knowing a precise FTP is really only necessary for pacing one hour TT race efforts.

The trouble with OP's method is he has to run two tests to get one result. So it is a two-day process. Running the two tests in succession on the same day doesn't seem like a valid way to go about it if you want to use the independent 5 minute test and independent 20 minute test. Not to mention physical differences of the rider on those two days contributing to error in the method.

I agree with this. Depending on which of two 5-minute efforts I choose from recent weeks, with this method by FTP could be calculated as being off by either -7W or +6W. One of those days I might have felt better, or the wind might have been blowing stronger or in a different direction. Doing them back-to-back would probably affect one or the other. Either you would hold back a little on the 5-minute or you would be baked for the 20-minute. I think the standard 20-minute test is accurate enough, and quite a number of coaches and trainers use it.

Stick to your 20 minutes result for now. Even getting testing of any kind right gets some time, do you really think your 20 minute effort was the absolute max you could have done? Don't overthink it, use whatever number you got as a baseline and go from there.

I've always thought 95% of 20 minute was way too high as well. But it's what everyone uses so at least the playing field is somewhat level.

You don't need two tests, just data that contains both a 5 min and a 20 min max. When you ride with power and collect data over time, these numbers are automatically tracked for you by many data analysis programs.

The important thing to realize is that all of these formulae are going to assume a power declination curve for a "typical" cyclist. But truthfully there's enough variation amongst cyclists that there's a good chance your power declination curve is going to be different than the formulae assume- I know mine is.

The way around this- sort of- is to just ride a one hour test. But most people aren't used to one hour max efforts, they're painful and they take practice to get right. Also note that I say "sort of". Because the definition of FTP is based on an assumption that there is one power value that everyone can hold for exactly one hour. But even this isn't true for everybody. Not to mention that there can be differences in FTP depending on what muscles you engage- different muscles use oxygen and clear lactate more or less efficiently- which means you might have a different FTP climbing or on a TT bike vs road bike.

Bottom line is that FTP is something of a squishy concept. Don't take any number you generate as sacrosanct. Because of all that, my opinion is to use the easiest formula based on the longest test you can complete well. For most people, this is 0.95 x ave power on a 20 min effort.

At first glance the OP estimation appears to be a logarithmic decay fit which seems reasonable to me, but is it right?

I've heard of similar testing methods to what the OP suggests, and you want to do both tests on the same day. The idea is to get a sense of how you fatigue during rides and factor that into your FTP. Doing both tests on different days negates that as you are fresh for both tests.

Exactly. This is the important stuff. FTP is not for its own sake, but for training programs.

+1

Thanks a lot for your helpful answers.

Here is the reason I'm a little obsessed about getting the right FTP. All the training plans I find online are based on power zones and power zones are determined by FTP. Each power zone seems to have significantly different training effects (see table from TrainingPeaks below). I'm beginning to see that it's not that clear cut but my original simple thoughts were since all power zones are determined by FTP, all I need to do is work on my FTP and everything else will automatically go up with it (which upon some further reading, seems not to be the case). When I do 10, 15 or 20 minute FTP intervals I want to make sure that I'm training at my FTP, not above in zone 5 and not below in zone 3 as the training benefits for lactate threshold (which I thought determines FTP) is lower for zone 3 and much lower for zone 5. I especially don't want to accidentally train in zone 5 because that will just be harder training for much less benefit.

However, training is not as simple as I thought and there are benefits in other zones besides increasing lactate threshold. I just don't understand them yet (what is plasma volume, slow twitch vs fast twitch muscles, increased muscle glycogen storage and their benefits, etc.?) @gregf83 suggested that I get the ballpark first and adjust the zones according to how hard the workouts are for me to complete. If I begin doing some interval workouts, will I be able to tell if I'm in the wrong zone? For example, will I not be able to complete a zone 4 workout of say 3 x 10 min FTP intervals with 5 min zone 2 rests in between if I were accidentally in my zone 5 instead of 4?

I'm still a little confused as I am new to all this power training. Hopefully, I'll understand better as I go on.

Thanks.


http://i.imgur.com/rMDC5xl.png

If you have trouble finishing your interval sets it is possible that your FTP is set too high. It's also possible that you hadn't slept well the night before, or hadn't eaten right, or were just having a bad day. Or that you just need to HTFU.

What's more likely is that you will complete the set but you will be more fatigued than you should be. This might be a problem or you may recover better than most and it won't. Either it's not like your workout is wasted if you are slightly out of your true zone. Remember that the FTP value is just an approximation and on any given day it's probably a few watts high or low.

Don't try to figure everything out at once. Get it in the ballpark first and collect data. It'll make more sense as you go. But I think 95 % of 20 minute max power overestimates what I can do in an hour.

It will never be exact. Some of that depends on your particular fatigue profile. Some riders just do better at shorter efforts, others at longer. But the question had me look at a recent road race. I estimated my FTP by testing, then I compared it to my best 60' NP in a road race. They were within 3%, which is a pretty good match.

I've found 95% to be pretty well spot on for me, but I tend to test with a bit of fatigue in my legs (if going by fitness/freshness on Strava, I'm still around -4 to +4 of freshness when I test). I also round up to the nearest 5, since it makes the structured training a little harder, but not so difficult that I can't finish intervals (I use a smart trainer for my structured interval training, BTW). As already mentioned, there is so much variability in day-to-day performance that having an exact number isn't what's important, but how you structure your workouts to account for your training load and improvement plan. i rarely spend much time at 100%, and structure my workouts to be above, or below, depending on my goals for that day/week/season. The number is just a guide, like the numbers on the weights in the gym. If you keep getting that number to go up in the long term, you're doing something right.

Also, when I test and get a new FTP at the end of each 6-week session, I can't get the same time in my new power zones as I could at the end of the previous session. For example, I do a lot of sweetspot training on Mon and Fri. At the beginning 2-3 weeks, I can manage a Monday session that will be 2, 30-min blocks followed by a 40-min block, separated by 5 min rests. On Friday, I can only manage the first two blocks (I ride M-F, with some weekends). By the end of the 6-week session, I can do all three blocks on Friday, after a pretty intense week. Take the weekend off, and retest on Monday.

Unless you're a world class athlete, this level of minutia really doesn't matter. Your body is not digital and there's no magic cutoff at LT or any of the "zone" boundaries. If you want to train for short duration power, you train well above LT. If you want to train aerobic base you train well below LT. If you're doing "sweet spot" work right around LT, it doesn't really matter if you're a couple percent under or over.

If you are conditioned to a level where ultra high-precision matters, you won't have to worry about it because your coach will tell you what to do :)

Since the OP is trying to find his "most accurate" FTP, and since FTP by its definition is the amount of power one can hold for an hour, why not just do an hour long test and be done with it?