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I recently picked up a powertap and have done a fair bit of riding around and a few races now with it on, so I've started to get familiar with some of the numbers. I would like to figure out what my functional threshold power (FTP) is and would like to know which methods are more accurate.

I know a 40km time trial is sort of the gold standard, but I find these so mentally tough that it's nearly impossible for me to give an honest effort outside of a race situation.

Nothing is going to be easy, I imagine as any interpolated ways of doing this will probably require maximum effort for a certain amount of time, but I'm hoping there is a reasonably accurate method that is easier mentally and physically.

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  • The 'gold standard' is the definition of FTP: ride as hard as you can for one hour. You may need to adjust pacing over a few tries so you don't burn out too early. However, trust me, this is the hardest way to determine FTP, but it's the closest you'll ever get to an accurate number. It's a great workout whatever the case. Nov 26, 2023 at 1:43

6 Answers 6

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First, get 'Training and Racing w/ a Power Meter' by Hunter Allen and Andrew Coggan. So incredibly helpful in learning about your device. Second, use WKO+ for analysis. I have been using it for 4 years and it is fantastic.

In reference to you question, I typically use the 20 min time trial as a good way of setting my training zones. After a solid warm up (typically with a 5 min LT--->V02 effort) and then proper rest I do a flat 20 min TT. I take the avg. power from that TT (not the norm. power) and multiply by .95 (or take 5% off, whatever is easiest). For example: a 300 watt average over 20 mins would indicate an FTP of 285.

What I do after that is keep an eye on my IF (intensity factor) and my TSS (training stress score). If that is all gibberish to you I would recommend getting the book!

http://www.peakscoachinggroup.com/Archivedarticles/Determining%20Your%20Lactate%20Threshold.pdf

http://home.trainingpeaks.com/power411.aspx

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The rider in question bought a Powertap hub. The option of doing the ramp test on a smart trainer was probably not common then. Today, I would suggest that newer riders should consider this, with some caveats. Riders who know they have high anaerobic power should consider doing the 20 minute test instead, but again with some caveats.

First, what's FTP?

As we increase our exercise intensity, the concentration of lactate or lactic acid in our blood rises. Below a certain threshold, lactate levels are stable. Lactate is part of the aerobic energy cycle, your body consumes it to create more energy, and below this threshold your body is in equilibrium. Above that threshold, lactate levels rise rapidly. You can't work sustainably above this threshold. It's often called maximal lactate steady state (MLSS) in some fields, it may be more commonly known as the lactate threshold or lactate inflection point, and I believe it's known as LT2 in exercise science (LT1 is when lactate levels first start to rise from rest). FTP is an estimate of the cycling power we produce at MLSS.

We could directly measure your blood lactate levels in a lab, and some people do this for information, but this is inconvenient for practical purposes. All the duration-based tests are estimators of power at lactate threshold. This means that people think that if you run the algorithm (e.g. 95% of your 20 min power in the 20 min test) you should a value that's close enough to FTP for most people.

Andy Coggan and probably others once wrote that 60 minute power is your FTP. To be more precise, we should say that he thinks 60 min power is an estimator of FTP. It's since been shown that most people can hold FTP for 40 to 70 mins. Coggan may have been working with well-trained cyclists when he wrote that.

2 x 20 minute intervals at FTP is commonly suggested as a workout. It is actually a fairly challenging one. If FTP were actually equivalent to 60 min power, then why does 2 x 20 even exist? We would expect to see threshold interval designs like 5 x 15 mins - try to exceed 60 mins, just broken up into chunks.

Ramp test - no learning curve, less stress

In the ramp test, you pedal. The smart trainer increases the resistance every minute (i.e. it's in erg mode, where the trainer adjusts resistance to hold you to an average power that the software tells it). You pedal until exhaustion. You take the power in the highest complete block, usually pro-rate the incomplete block, then take 75% of that as an FTP estimate. This may sound intimidating to new riders, but it is over pretty fast and you won't be that tired afterwards. The test feels easy, then the challenging section onsets quickly and the difficulty really ramps up. You aren't suffering for long. It should also be pretty clear when to stop, in that you really can't push the pedals.

If you Google, you should find that the ramp test is accurate enough for most cyclists. You should find that most cyclists' FTPs are 70-80% of their maximum power on the ramp test. Ramp tests use 75% as a default multiplier. Be aware that the ramp test is directly measuring your maximal aerobic power (MAP), i.e. at this power you're at or near VO2max (your aerobic energy system is at maximum output). We've essentially determined that most people have their threshold power at about 75% of MAP. (Added after R Chung comment.)

For beginners, you don't need to learn to pace your effort. You just go as hard as you can until you physically can't turn the pedals over. It's also relatively little stress on the body, i.e. you recover quickly and can get back to training. Pacing a 20 minute effort is not a trivial skill, especially when you have no reference point. Thus, I think that if you have access to a smart trainer, most people should start with the ramp test. The learning curve for the ramp test is much shallower than the 20 min test.

However, after testing, you still want to check if you can hold intervals. Riding at threshold should feel challenging but sustainable. Your heart rate should rise but hit a ceiling (e.g. I believe mine is 169-171 bpm, judging from observation). If you're really gasping for air and your heart rate keeps drifting higher, you may be riding above threshold. Training software has a bias adjuster, where you change the difficulty in 1 percentage point increments up or down. Feel free to use this if you can't maintain power. In particular, a minority of athletes might have the ramp test significantly underestimate or overestimate their threshold power.

TrainerRoad's default is the ramp test, and it can also adjust its estimate of your FTP based on your feedback after workouts (i.e. rate the workout difficulty). Wahoo SYSTM (formerly Sufferfest/SUF) recommends its 4 Dimensional Power test once a year, and it recommends its enhanced ramp test in the interim. So, in some sense, both these companies seem to be leaning towards the advantages of the ramp test. I am basically telling you to do what TrainerRoad does, just using your own intuition rather than whatever they have programmed.

The ramp test will get you to near your maximum heart rate. I don't know if a subset of athletes may have medical contraindications that rule this test out. Obviously ask your cardiologist, but be aware that some might be unfairly biased against strenuous exercise.

20 minute test - cruel, brutal, possibly more accurate for some

In the proper version of the 20 min test, you warm up, then you do 5 minutes all out, then you rest 5 minutes. Then you do 20 minutes, and you take 95% of the average power as your FTP estimate.

The accepted answer casts the 5-min block as a hard warmup effort between threshold and VO2max power. I believe this is actually not quite true. You are supposed to go as hard as you can. This is to deplete your anaerobic reserves. If you check the Zwift 20 minute FTP tests, you'll find that the 5 minute session is at something like 110% FTP, and you often get a 10-min rest before the 20-min effort. In my last 20 min test, my 5-min interval was a bit over 130% of my FTP estimate. It's interesting to know your 5-min power as you can estimate your VO2max based on that, and you can track your threshold as a percent of 5-min power - if it gets high enough, you may want to do more VO2max work to raise your ceiling.

If you know you're good at anaerobic efforts, I think it's better to work up to the 20 min test. It should produce a more accurate FTP estimate. The alternative is to keep doing the ramp tests, adjust workouts based on intuition, and perhaps come up with a better multiplier for yourself (e.g. I think mine is probably 0.7 vs the default of 0.75).

The downside is that doing a 5 min all-out effort, then a short rest period, then a maximal 20 minute effort is absolutely awful if you are really pushing yourself. It's about an hour long including warmup and cooldown. You need to learn to pace yourself. Having a previous accurate FTP estimate really helps with that, but it doesn't change the fact that the effort sucks. For beginners, your first few tests can give inaccurate estimates just because you're learning how to pace a 20 min hard effort.

The dual 8-min max efforts (FTP is 90% of the higher average power) is another test in this format. I think this protocol doesn't need you to deplete your anaerobic capacity. I am not sure how accurate it is.

The Wahoo 4DP test is even more awful than the 20 min FTP test, because it has an all-out 1 min effort at the end. It is available as a free workout on Wahoo's platform if you are so inclined. It will get you a sense of how well your power at various intervals compares to other riders. Of course, some of the power-duration models below can do the same.

Alternatives - power-duration models

Consider the concept of the power curve. That's the jagged line on the graph below (my data); we'll discuss the smoothed line shortly.

enter image description here

This is a graph of power on the y-axis versus duration on the x-axis. The jagged line was my empirical power curve based on my efforts over a 6 week period - those have included an FTP test, so my 5 minute power is truly an estimate of my fresh max power. But I haven't sprinted, nor have I tried an hour-ish TT.

People have proposed mathematical models like the Critical Power model. I believe that the Monod-Scherrer model is the first. If you get people to do 2-4 maximum fresh efforts at certain durations, you should be able to mathematically estimate their theoretical power for any duration within a certain window (e.g. 1 min to 40 min). The Critical Power model is one of these. You typically do a 3-min and a 12-min one. Now, as duration goes to infinity, that model will say that your theoretical power goes towards an asymptote. That asymptote is known as critical power. It's usually pretty close to FTP. The smooth curve in the graph is from the Monod-Scherrer model, and the circles are the datapoints the model used. There are more sophisticated alternatives, e.g. Morton's model adds a parameter for very short duration efforts (requires a max effort around 5s).

Critical Power is highly correlated with FTP, but it isn't FTP as discussed here (open access). In fact, it's a bit above FTP on average, but the difference varies for different people and some people have FTP > CP. The BikeRadar article did say you can take 94% of your critical power as an FTP estimate, although the percentage will vary individually. For VO2max intervals, I think the power target isn't as important as just going as hard as you can sustain.

Comments on the FTP formula

One answer mentioned a formula to estimate FTP based on age, weight, and gender. I'll argue that this is a poor choice. The formula is by Joe Friel and is as follows.

Step 1. Double your body weight in pounds (1 kg = 2.2 lbs). Example: A body weight of 154 pounds (70 kg) estimates an FTP of 308 watts (154 x 2 = 308).

Step 2. Subtract 0.5% for every year beyond age 35. Example: If the above 154-pound rider is 50 years old...

Step 3. Women riders can subtract 10% from the estimated FTP as found in steps 1 and 2 above. ...

First, if you run the math in step 1, you'll see that the formula estimates that a 35 year old man has a 4.4 W/kg FTP. That is very fit. That is comfortably in Zwift Cat A. That is probably well above the average fitness of US Cat 3 road racers. It isn't pro-quality, but 4.4 W/kg would tear it up on almost all group rides. The estimate for a 35-year old woman is 3.96 W/kg. This would have you tearing up most mixed-gender group rides.

Second, you could tweak the parameters in the formula to be more accurate. But even if you got better parameters, you are still left with an estimate of the average FTP given age, weight, and gender. Someone will come onto a forum and say my FTP is 100W above the formula! Another person will come and say I can't hold my formula power for 5 minutes!

Imagine a scenario where your FTP, or your max HR, or whatever is an important training parameter, and you can't estimate it easily, but you need a number right now. It is a perfectly sound strategy to plug the average in, provided the estimate is accurate (Friel's estimate is biased very high), until you have better data. If you know nothing at all, then you are more likely to be close to the average than you are to be far away from it. The problem is that you can estimate your FTP easily enough. If you needed an estimate right now, it would be better to ride to perceived exertion and get a ballpark from there. Also, as I mentioned, the ramp test is a pretty short test and it isn't very strenuous.

The lived experiences of ordinary cyclists on ramp tests

The analysis of lived experiences is important in some academic disciplines. It can help us understand social or cultural phenomena in more detail, e.g. the experience of illness.

That said, this part of the answer is less serious. I just wanted to show that beginners need not be afraid of the ramp test. So I checked YouTube to see if I could find videos of ordinary cyclists doing ramp tests. Not fit cyclists, and definitely not pros. If you peruse this section, remember that humans come in a range of shapes, sizes, and aerobic potential.

Benji Naesen is a cycling commenter on the Lantern Rouge podcast. He's relatively new to structured training. Without offense to him, he's closer to average person on the street in terms of fitness and he's also on the huskier side. For the sake of entertainment, he did his first ramp test, and then a few days later he did the 20 minute test. His assessment at the end of the video is that the 20 min test was a lot harder than the ramp test, and he also swore a lot more during the 20 min test. He got 198W on the ramp test and 190W on the 20 min test. That's a 4% difference, which is not huge. Moreover, check his average power during the 20 min test. He's doing negative splits (i.e. power declining through the test). If he had maintained an even pace in the 20 min test, his results would be even closer.

Here, Leonard Lee, an older cyclist who is also a bit on the heavier side, attempts his first ramp test. It was clearly effortful for him. But he persists.

Here, Ed Laverack's partner Charlie does a ramp test after not exercising for 8 months. She reflects on the experience afterward. Laverack is a former pro, but his partner is not.

Sam Flynn started a YT channel to chronicle her weight loss journey. Here, she also survives the experience, demonstrates improvement, and offers reflections.

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  • 2
    (1). If one wants the "easiest" way to determine FTP, first ask "how much accuracy/precision do we need?" For training purposes, the answer is "probably within a few percent." FTP estimates that end in 0 or 5 are almost surely good enough, and improvements from test to test of 1 or 2 watts may be unreliable. (2). Andy Coggan doesn't recommend any version of "the 20-minute" test. That test is Hunter Allen's. (3). The ramp test was originally set up to estimate VO2Max. Multiplying by a fixed percentage is a roundabout way to get a FTP estimate based on a VO2Max estimate.
    – R. Chung
    Nov 25, 2023 at 15:29
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    This is a great answer, but for the "need a number right now" problem, one might also look at this widely used table of power outputs at different fitness levels (which is from Coggan's book, I believe).
    – Adam Rice
    Nov 25, 2023 at 16:49
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    Transform your power-duration curve into a work-duration curve and plot that. How linear is it out to an hour, two hours, four hours, six hours? Typically, it's pretty linear out to maybe an hour and then curves a little. How close it the slope at various durations to your estimated FTP?
    – R. Chung
    Nov 26, 2023 at 20:00
  • About the name FTP: when Andy Coggan introduced the concept, it was clear that he was thinking about the power that elicited MLSS. However, measuring MLSS was a laboratory measurement and he was looking for something we could do with a power meter, i.e., he was looking for a "functional" test rather than a "laboratory" test. He later listed several ways to estimate this threshold (his "7 deadly sins...er, ways of determining your FTP" (that was really the title of his post))
    – R. Chung
    Dec 30, 2023 at 2:08
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Joe Friel claims a 30-minute TT which is not part of a race (ie, when the athlete is less motivated) estimates FTP. He also suggests FTP can be estimated from weight and age, though clearly this is only going to hold for athletes who are similarly trained. Other estimations of FTP include the NP from a hard 1 hour mass start race.

See this 7 deadly sins article for more.

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  • If you check Friel’s math, that’s 4.4 W/kg for 35 year old men. That’s not pro level, but it is very fit. His numbers don’t apply to the population average, so the formula is a poor one. Even if you got better numbers, you are still estimating the average FTP given age and sex. That may or may not work for an individual.
    – Weiwen Ng
    Nov 24, 2023 at 17:39
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There are lots of different field tests approaches. I've been using the Carmichael one (two 9-minute full out TTs with a cooldown between them).

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  • That's similar to what I was instructed by them (2006), 2 x 3 mile max effort or 8 minutes on trainer. I wonder if it's been changed? I think they increase that for advanced athletes who have very consistent time between the two.
    – imel96
    Nov 27, 2013 at 5:51
  • They did change from 2x3 miles to 2x9 minutes. Carmichael talks about in the time crunched cyclist Dec 20, 2013 at 3:26
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You might interest a friend of similar skill in a 40km time trial? You could both work on beating the other which might help you with the mental toughness outside of a race.

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I wrote a quick guide outline some of the best and effective testing methods you can use. These are word for word how they are delivered to my own athletes. Enjoy!

How to find your functional threshold

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    Nov 27, 2013 at 1:16
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