The article was first published in 2022 and was updated in October 2026 by Sandra Schuberth
Indoor training on smart trainers is controlled by pedalling power, which is displayed in watts. Power in watts is the linchpin of it all. The maximum pedalling power varies depending on fitness level, body weight – and, crucially – the duration of the exertion. During a sprint, a multiple of the sustained power output is possible. The measure most commonly used to gauge endurance capacity is the FTP power (FTP = Functional Threshold Power). This is the maximum power output over one hour.
From the FTP, you can Training zones to derive metrics that describe training intensities. On hills in particular – whether indoors or outdoors – watts per kilogram are the measure that determines hill-climbing pace. FTP provides an immediate indication of where an athlete stands in the performance pyramid: The spectrum ranges from 1.5 W/kg (untrained) to 6.5 W/kg (absolute world class). Regularly testing your FTP is one way of tracking your performance progress.
As maintaining maximum power output for over an hour is very demanding, the FTP test is usually shortened and the FTP power is estimated based on the power output over 20 minutes.
Anyone wishing to get to grips with the basics will find in our Questions and answers about the FTP test More on test conditions, the validity and limitations of the measurement.
FTP tests by Zwift
The article explains the two step tests and the 20-minute FTP test, which are available in the workout selection shown here.
Which FTP test is right for me?
Zwift uses an FTP baseline for the specified workloads. The Lite version is aimed at cyclists for whom the standard step test starts at too high a level. Those who can maintain as consistent a power output as possible over 20 minutes should choose the FTP test. The result is an estimated value, which should be refined later through training and longer sessions.
| If one … | Then ... |
| does not yet have an FTP value | Placement test |
| already has an FTP value, but wants to check whether it is correct | FTP test |
1. Level tests or Level Test Lite for an initial estimate of FTP
If you don’t yet have a tested value, you can start by using an estimated value or complete a step test for guidance. Zwift offers two options for this. The standard step test increases the power output by 20 watts every minute, starting from 100 watts. This test feels very easy at the start. However, once you exceed your personal aerobic threshold, it only takes a few minutes before you can no longer turn the cranks. Zwift estimates your FTP as 75 per cent of the last completed stage. So, if you can manage 300 watts, your FTP will be displayed as 300 * 0.75 = 225 W. A variation of this test is the ‘simple’ step test. Here, the test starts at 50 W but ends at a maximum of 250 watts (relevant only for beginners and very light riders). The step test is simple but not very accurate, as the short duration of each step causes distortions due to anaerobic energy contributions. However, the test is quick and suitable for an initial estimate. Zwift offers both variants. The image shows the version for very light riders or those who are not very fit.
2. FTP test
Unlike a step test, the 20-minute test measures endurance performance through its longer exertion phase. Zwift’s standard FTP test lasts 45 minutes.
Procedure: After the warm-up, there are two intense intervals lasting three and two minutes respectively. These are intended to deplete your anaerobic energy reserves before the actual test. If the initial FTP value is set too high, even these warm-up intervals may prove too strenuous.
This is followed by 20 minutes of free riding. This is the actual test. The aim is to maintain as high and consistent a power output as possible throughout the entire duration. Zwift estimates your FTP based on 95 per cent of your average power output during this section.
If your performance drops, repeat the FTP test
It is advisable to start the ride using your estimated FTP value. Towards the end, you can push yourself a bit harder, if possible. If your performance drops significantly during the 20 minutes, you’ve started off too fast and should repeat the test, as the average will be higher if you cycle at a steady pace.
The Zwift test protocol is in line with TOUR’s recommendations. The FTP power determined in this way and the zones derived from it are very useful. If the test doesn’t go perfectly the first time, it’s easy to repeat. Zwift can detect a higher FTP even without a separate test, for example during a free ride, a workout or a race. To do this, the platform takes into account not only new 20-minute best performances, but also intense efforts of other durations. If Zwift reports a higher value, you should check whether the resulting training intensities are appropriate in practice.
What do I do with the FTP result?
The value determined serves as a starting point for watt-controlled workouts. In subsequent sessions, you should check whether the specified intensities match your own perception of exertion. If, on repeated occasions, many intervals feel unexpectedly easy or barely manageable, the test conditions and FTP setting should be reviewed. Subsequent tests should, where possible, be carried out using the same protocol and under similar conditions to ensure comparability.
Strengths and weaknesses of the Zwift FTP tests
The FTP test is based on riding at full capacity – as a general rule, not just on Zwift. It’s always tough, and the result depends heavily on your motivation to give it your all. Riding at full capacity also means you need to be in good health. Anyone who doesn’t usually push themselves to their limits should have a sports medicine check-up beforehand.
You should prepare thoroughly for the test. In addition to tried-and-tested smart trainer equipment, the following items are essential:
- Cooling (fan)
- No disruption/interruption
- Motivational visual and audio material
When carried out correctly, the FTP test provides valuable key performance indicators for assessing fitness.
Critics argue that the FTP test reveals nothing about the physiological causes of performance – for example, how the body provides the energy required for the measured performance. This criticism is valid. Furthermore, the FTP – extrapolated from a 20-minute session to an hour – may be subject to error. However, these values can be verified using more data from training and competition. By combining this with further tests over shorter periods, it is possible to draw more detailed conclusions about metabolism. INSCYD offers such analyses, although these do incur costs.
As an alternative or in addition, standard laboratory tests are available (lactate testing and/or spiroergometry), which can also provide further information and do not always need to be carried out to the point of maximum exertion. Laboratory tests on their own have the disadvantage that they are usually carried out too infrequently – partly because they are expensive. Furthermore, not all laboratory tests are equally good or valuable. It is difficult to assess their quality.
The A ‘do-it-yourself’ approach to the FTP test It makes it easy to just get started and gain experience. Anyone who regularly tests themselves and rides a lot on a smart trainer or with a power metre can easily get a fairly comprehensive picture of their performance level. This can make further diagnostic tests unnecessary. You can easily tell whether your FTP has been tested realistically by comparing it with real-world data. If the FTP test predicts 250 watts but you only manage a maximum of 220 watts during an hour-long climb at full effort, then it’s clear that the test was too optimistic and fatigue was underestimated. The actual FTP value is therefore 220 watts.
Taken together, all these methods – the FTP test, laboratory diagnostics and power meter data – provide the most comprehensive picture. Regardless of the testing method used, the results should always be scrutinised for plausibility.
When and how often should FTP tests be carried out?
It is advisable to have a test carried out before each intensive training phase to gauge your fitness level; a A repeat examination should be carried out no sooner than six to eight weeks later is advisable and helps to monitor progress. You should always well-rested and with plenty of energy Go for a run. This means that the runs should take place during a recovery phase. The Performance measurement should be as accurate as possible – if available, use a power metre as a data source. In the long run, the absolute accuracy of power measurement is more important than one might initially think, as only reliable data is of value in the long term and makes even small improvements visible.
As the test itself is physically demanding, it is not advisable to carry out FTP tests on a regular basis. You need to weigh up the benefits of always following the same protocol (comparability) against the additional training load imposed by the test protocol. Nor should one underestimate the mental strain involved in undertaking an all-out test. The energy required for this might be better spent on an (indoor) race.
The You can also do the FTP test outdoors. But bear in mind: when cycling outdoors, most cyclists achieve slightly higher power output than indoors, and higher power output on climbs than on flat terrain. To track progress in power output, you should always carry out tests under comparable conditions.
Indoor FTP tests on Zwift are a good place to start
Zwift’s FTP tests are ideal for getting an initial idea of your fitness level and monitoring your progress. Cyclists who do a lot of high-intensity intervals and compete in races using a power metre will gain additional and often more relevant data this way than from a single FTP test. Personal bests for power output are usually only achieved during a race.
Robert Kühnen
Editor