FTP — functional threshold power — is probably the most quoted number in amateur cycling. Riders compare it at group rides, obsess over it after a hard effort, and build entire training blocks around improving it. Yet most cyclists who track it regularly would struggle to explain what it actually represents. It is a proxy, a useful approximation, and a decent enough training anchor — but only if you understand what it is measuring and where it falls short.
What FTP actually is
Functional threshold power is the average power you could sustain for approximately 60 minutes of all-out effort. That definition sounds simple, but the physiology underneath it is worth understanding properly. FTP sits close to what exercise scientists call the maximal lactate steady state (MLSS) — the highest intensity at which the body can still clear lactate as fast as it is produced. Below that point, you are in a manageable equilibrium. Above it, you are spending from a limited account that will eventually empty. FTP is roughly where that line sits.
Dr Andrew Coggan originally formalised the concept as a field-based alternative to laboratory lactate testing. The appeal was obvious: no needles, no lab booking, just a 20-minute effort and some arithmetic. Multiply your 20-minute average power by 0.95 and you get a usable estimate. That estimate is good enough to anchor your training zones, calculate training stress score (TSS), and compare your fitness over time. It does not tell you your exact MLSS — but for most riders, that level of precision is not what they need.
One clarification that often trips people up: FTP is not your VO₂max pace. It is not your anaerobic ceiling. It sits lower than both. On a long, hard climb at threshold pace, you should feel controlled discomfort — breathing is laboured but rhythmic, your legs are accumulating fatigue but not screaming, and you are aware that you cannot hold a proper conversation. That sensation is the real-world signal that you are riding at or close to your FTP. It is also the reason why understanding your FTP in the context of structured training matters so much more than chasing the highest number you can post on a test day.
How FTP shapes your training zones
The reason FTP is so central to structured training is that it becomes the denominator for everything else. Your cycling training zones are defined as percentages of FTP — and getting those percentages right is the difference between a productive training week and a slog that leaves you flat. Zone 2 endurance work sits around 55–75% of FTP. Sweet spot training lands at 88–93%. Threshold intervals sit right at 95–105%. Each zone targets a different physiological adaptation, and all of them rely on your FTP being reasonably accurate.
This is where a lot of riders quietly go wrong. If you set your FTP too high — which is easy to do if you had a great day for the test, were slightly over-motivated, or took the 95% multiplier from a 20-minute effort that was more of a sprint finish than a sustained effort — every subsequent zone is miscalibrated. Your sweet spot rides become threshold efforts. Your threshold intervals become something harder and shorter-lived. You accumulate fatigue faster than fitness. The training plan looks the same on paper, but the stimulus it delivers is entirely different. Knowing how to set your zones from your FTP correctly is not a minor detail — it shapes whether your training is actually working.
What FTP does not tell you
FTP is one number representing one aspect of fitness. It says nothing about your sprint, your VO₂max, your ability to sustain repeated hard efforts, or how well you recover between efforts. Two riders with the same FTP can have entirely different race performances depending on those other capacities. A 300-watt FTP means one thing on a four-hour Gran Fondo and something completely different in a short, punchy criterium with repeated accelerations above threshold.
There is also the question of accuracy. Research published in sports science literature has repeatedly shown that FTP tests — particularly the common 20-minute protocol — often overestimate what a rider could actually hold for 60 minutes. For time-crunched cyclists who do a lot of intensity and relatively little long aerobic work, the 95% multiplier is frequently too generous. The honest read is that FTP is an approximation, not a laboratory-grade measurement. That is fine — it is still useful. But it means you should hold the number loosely and pay attention to how your actual rides feel at the power outputs your zones prescribe.
One practical response to this is retesting regularly. FTP changes as you train. Do enough structured work and it climbs. Take a few weeks off, stop doing any intensity, and it will drift down. Retesting every six to eight weeks gives you a current anchor and also gives you objective feedback on whether your training is moving the needle. If your FTP has not shifted in four months despite consistent work, something in the training stimulus is wrong — and that information is worth having. When targets need to shift but you do not want to go through a full retest, knowing how to adjust training targets without retesting can bridge the gap.
Using FTP as a tool, not a trophy
Let's be direct: the rider who treats FTP as a social media metric is almost certainly misusing it. The point of knowing your FTP is not to announce it; it is to train more precisely. When your FTP is well calibrated and your zones are set correctly, every ride has a purpose. Easy rides are genuinely easy — you are actually building aerobic base rather than grinding at a medium intensity that develops nothing particularly well. Hard rides are hard in the right way, delivering the threshold or VO₂max stimulus you need without destroying your ability to train again two days later.
The useful way to think about FTP is as a dial that tells you where your fitness currently sits. A higher FTP means you can produce more power at the intensity where aerobic and anaerobic metabolism roughly balance — which means you can ride faster for longer before things start to unravel. Training below and around FTP builds that capacity progressively. That is what makes it central to structured training: it is not the goal itself, it is the measure you use to make sure you are training in the right places.
If you have never tested your FTP properly, the 20-minute protocol on a trainer after a proper warm-up and a ten-minute all-out opener is the most accessible starting point. Do it when you are rested, fuel it properly, and pace the 20 minutes so the last five minutes are the hardest. The number you get will be imperfect, but it will be good enough to build from.
Related reads
- How to set your training zones from FTP
- How to adjust training targets without retesting
- FTP for cyclists: the complete guide
Sources
- Coggan AR, Allen H. Training and Racing with a Power Meter. VeloPress, 2010.
- Jeffries O et al. "FTP is not equivalent to lactate parameters in trained cyclists." International Journal of Sports Physiology and Performance, 2021.
- Treff G et al. "The relationship between FTP20 and FTP60 and their validity against anaerobic threshold." International Journal of Sports Physiology and Performance, 2018.
- Faude O, Kindermann W, Meyer T. "Lactate threshold concepts: how valid are they?" Sports Medicine, 2009. doi:10.2165/00007256-200939060-00003