What is FTP and how accurate is the 20-minute test?
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Prepared by the FredCoach science team, AI-assisted, from the cited sources · Performance scientist
In short. FTP is an estimate of the highest power you can sustain without the effort running away from you, and the classic test calculates it as 95% of your average over 20 minutes all-out. In trained cyclists it is right on average, with a typical error of 3 to 6%, and in amateurs it tends to sit somewhat below their real threshold. It is a useful, repeatable anchor for your zones, not an exact physiological boundary.
What is FTP?
FTP stands for functional threshold power. Hunter Allen and Andrew Coggan popularised the idea in their 2006 book on training with a power meter: the highest power you can hold in a near-steady way for a long time, which they placed at around an hour.
Because an all-out hour is hard and impractical, they proposed a shortcut: 20 minutes as hard as you can, keeping 95% of the average. If you average 260 watts, your FTP would be about 247. The 5% taken off accounts for the fact that you can hold 20 minutes harder than an hour.
There is a real physiological concept behind it: there is an intensity below which blood lactate and oxygen uptake settle, and above which they keep rising until you stop. Labs measure it in several ways (lactate threshold, maximal lactate steady state, critical power). FTP is a way to estimate it with a power meter and without pricking your finger. The question is how close it gets to the real thing.
How accurate is the 20-minute test?
In trained cyclists, it is right on average
A 2019 study compared the FTP of 15 trained cyclists with their maximal lactate steady state, measured in the lab. On average, FTP came out just 1.4% higher, and the two values tracked each other closely. But the typical error was 4.7%, and the limits of agreement show that, for an individual rider, the difference can approach 10% either way.
Training level mattered: in the better-trained riders the typical error was 3%; in the less-trained ones, 6.4%. For an FTP of 250 watts, that is a typical error of about 8 watts in the better-trained and about 16 in the less-trained.
In amateurs, it tends to read low
A 2018 study with 20 cyclists compared FTP with the lactate threshold from a step test. In the trained riders there was no significant difference. In the recreational ones, however, FTP came out 6.5% below their threshold on average, and the less relative power a rider had, the bigger the gap.
Both findings come from small studies of 15 and 20 cyclists. A 2021 review that gathered 15 studies on the test reached the same view: the test is repeatable, but its agreement with other threshold markers has wide margins, and the evidence is still limited and focused mostly on trained men.
For most riders, FTP is not what you can hold for an hour
The original definition talked about an hour. The studies say something else. In a study of road cyclists of different levels, the time they lasted at their FTP was, as a median, 35 minutes in recreational riders, 42 in trained, 47 in well-trained and 51 in professionals. And it varied a lot from rider to rider.
Another 2022 study with 13 cyclists went further. At their FTP they lasted about 34 minutes and finished with high lactate; 15 watts above it, about 22. In both cases oxygen uptake settled without reaching its maximum. The authors concluded that FTP does not mark the boundary between effort that can settle and effort that cannot: their data suggest that, in these riders, it sat somewhat below it.
So not lasting an hour at your FTP does not mean your test was wrong. It is normal.
FTP and critical power: similar, not interchangeable
Critical power is calculated from several maximal efforts of different lengths (for example 3, 7 and 12 minutes) and describes how your power falls with time. In a study with 17 trained cyclists and triathletes, critical power came out on average 7 watts above FTP (256 versus 249). The correlation was very high, but for an individual rider critical power could sit anywhere from 19 watts below to 33 above their FTP.
That is why a 2022 review on cyclists' power profiles recommends not relying on a single test such as FTP and combining several maximal efforts of different lengths. A single test sums up a single day: your state, your rest, your pacing and even the terrain.
Terrain matters: in a study with nine junior cyclists, FTP done on a climb came out 14–15% above their critical power and threshold measured in the lab. It is a small study with teenagers, but it is a reminder that a test on the trainer and one on a climb are not the same measurement.
So is it any use?
Yes, a lot, as long as you read it for what it is. An FTP is an estimate with a margin, not an exact number. It is repeatable, cheap and done with what you already have, which makes it a good anchor for your training zones and for seeing whether you improve.
What helps make the number reliable
- Doing it rested, with nothing hard the day before: fatigue and a bad night take watts away.
- Repeating it in the same conditions: the same place (trainer or the same climb) and the same warm-up.
- Pacing it: starting a little below what you think and pushing at the end. Going out too hard sinks the average.
- Reading the result as a range of a few percent either way, especially if you are starting out.
These are common coaching practices, not something measured in a specific study (the sleep part does have studies behind it). Zones as a percentage of FTP (Coggan's, the most widely used) are also a useful convention, not a lab result. If you are an amateur, bear in mind your FTP may read a little low and your zones may therefore be slightly conservative.
Keep reading
- Is lactate bad for cyclists? From villain to fuel
- Does lack of sleep hurt your cycling performance?
- How much strength training does a cyclist need, and when?
FAQ
Why can't I hold my FTP for an hour?
Because almost nobody does: in the studies, time at FTP was about 35 minutes in recreational cyclists and about 50 in professionals, with a lot of variation between people. Not lasting an hour does not mean your test was wrong.
Does the 20-minute test give the same result on the trainer as on a climb?
Not necessarily. In a small study with nine junior cyclists, 20 minutes on a climb came out 12% above what their lab tests predicted. The sensible thing is to always compare tests done in the same place.
How often should I repeat the test?
No study has set a frequency. In practice, coaches repeat it every few weeks or months, or when training has changed and the zones feel too easy or impossible.
Is FTP the same as the lactate threshold?
They are very close on average in trained cyclists, but they are not the same. In recreational riders FTP tends to come out somewhat lower, and for any individual the difference can be several percent either way.
Sources
- Borszcz FK, Tramontin AF, Costa VP (2019). Is the functional threshold power interchangeable with the maximal lactate steady state in trained cyclists?. International Journal of Sports Physiology and Performance 14(8):1029–1035 · doi
- Valenzuela PL, Morales JS, Foster C, Lucia A, de la Villa P (2018). Is the functional threshold power a valid surrogate of the lactate threshold?. International Journal of Sports Physiology and Performance 13(10):1293–1298 · doi
- Mackey J, Horner K (2021). What is known about the FTP20 test related to cycling? A scoping review. Journal of Sports Sciences 39(23):2735–2745 · doi
- Sitko S, Cirer-Sastre R, López-Laval I (2022). Time to exhaustion at estimated functional threshold power in road cyclists of different performance levels. Journal of Science and Medicine in Sport 25(9):783–786 · doi
- Wong S, Burnley M, Mauger A, Fenghua S, Hopker J (2022). Functional threshold power is not a valid marker of the maximal metabolic steady state. Journal of Sports Sciences 40(23):2578–2584 · doi
- Karsten B, Petrigna L, Klose A, Bianco A, Townsend N, Triska C (2021). Relationship between the critical power test and a 20-min functional threshold power test in cycling. Frontiers in Physiology 11:613151 · doi
- Leo P, Spragg J, Podlogar T, Lawley JS, Mujika I (2022). Power profiling and the power-duration relationship in cycling: a narrative review. European Journal of Applied Physiology 122(2):301–316 · doi
- Vinetti G, Rossi H, Bruseghini P, Corti M, Ferretti G, Piva S, Taboni A, Fagoni N (2023). Functional threshold power field test exceeds laboratory performance in junior road cyclists. Journal of Strength and Conditioning Research 37(9):1815–1820 · doi