Functional Threshold Power (FTP) is one of the key performance metrics for cyclists who want to train and race with power.
It is generally defined as the maximum average power, measured in watts, that a cyclist can sustain for an hour.
While this has applications in its own right – if you race 25-mile time trials in the UK, for example, it’s a very useful figure to know if you’re racing with a power meter – it’s more commonly used to set training zones and for measuring improvements (or deteriorations) in fitness.
FTP is also one of the key figures used to determine all manner of things on Zwift, such as training zones and race categories.
How to sign-up to Zwift
Visit the Zwift website to sign-up for a free 7-day trial. After your trial period ends, Zwift costs £12.99 / $14.99 per month.
Don’t worry if this is all Greek to you though, because you can check out our full guide to FTP and why it matters for the full run-down. Here we’re going to focus on how to use Zwift to complete an FTP test.
While you can complete an FTP test on the open road, it can be difficult to find a suitable stretch of tarmac, free of interruptions such as junctions, traffic lights, road works and congestion. Given how downright unpleasant an FTP can be, there’s nothing worse than having to stop your effort after 15 minutes.
Using the turbo trainer removes those variables and allows you to focus on producing your best performance.
Why should I take an FTP test?
Before you embark on any kind of training plan, like those available on Zwift, it’s worth setting a baseline FTP figure for a couple of reasons.
“If your power zones aren’t accurate, you’ll be training in the wrong zones, and not targeting what you’re intending to,” says Rowe.
Having a baseline figure from the very beginning of your training plan will also allow you to know how much progress you’re making throughout the plan.
“Get a couple of weeks under you belt, then get stuck in,” he says. “You’re not going to get a great score, but it helps establish where you’re at.”
It’s particularly relevant at this time of the season, Rowe adds – particularly if you’re just coming back to training after a break. “You might be a long way off where you want to be but, at this time of year, that’s where you should be,” says Rowe. “Setting an FTP now will help you to evidence your improvements later on.”
Why should I use Zwift for an FTP test?
One of the main reasons to use Zwift is that it makes it all very simple – the test protocols are well signposted and easy to follow. This also means it’s very repeatable, so you can be sure that your results are comparable every time.
If you have a smart trainer, then Zwift can also use ERG mode to control the resistance of the trainer to ensure you hit the specific power levels required in a ramp test, or in the warm-up for a 20-minute time-trial test. We’ve cover those options in more detail below.
Once you’ve set your FTP, Zwift can then adjust all of the workouts and training plans to your specific level of fitness.
You’ll also then know which race category you fit into, based on your current fitness level, because these are decided according to FTP in watts per kilogram (w/kg).
FTP test options
Outside of simply riding as hard as you can for an hour (which is very hard to pace correctly and can also be pretty dull), there are two main ways to test FTP, both of which are available on Zwift.
First, there’s the traditional 20-minute time-trial test. After a warm-up, you perform a 20-minute interval at maximum effort. Record your average power and then subtract 5 per cent to determine your FTP (Zwift will do this automatically for you).
The second way to calculate FTP is to perform a ramp test. As the name suggests, the ramp test involves performing intervals at ever increasing power levels until failure. Zwift then calculates your FTP based on 75 per cent of the maximum power interval that you reach.
How to test your FTP on Zwift
If you’re new to Zwift but you already know what your FTP is, you can manually enter it on your profile page or on the workout page – it displays your FTP on the bottom right of the window, and to change it you simply need to click it.
Alternatively, Zwift will calculate your FTP from general riding in the game or from racing. Zwift will automatically calculate your FTP on every ride, using the maximum 20-minute average power you record on each ride, but will only notify you if it detects an increase over your current score.
However, the best way is to perform one of the three specific FTP workouts available in the training page on Zwift.
Classic FTP tests
The first workout, which is simply called ‘FTP Test’, is Zwift’s standard protocol.
It starts with a long, easy warm-up, followed by a few ramps and a 5-minute effort. After that, you get a rest period, before performing the 20-minute maximum effort test interval.
Zwift will then subtract 5 per cent from your average power during that test interval to extrapolate it out to an hour.
For example, if you average 300 watts for the 20-minute test interval, you FTP would be 285 watts.
The second FTP test on Zwift is called the ‘FTP Test (shorter)’. It’s simply a compressed version of the first test.
The 20-minute maximum effort test interval is the same, so it’s not any easier, the only difference is that the initial warm-up is shortened to save time.
This test has the advantage of being a reasonably long interval, so it tests your aerobic capacity very well and can give accurate results. However, Rowe says it can be a daunting task for many people, because it’s always going to be a very hard test and is difficult to pace properly, especially for beginners.
With that in mind, Zwift has recently introduced a different kind of test; the ramp test.
The ramp test
As the name suggests, the ramp test involves performing intervals at ever-increasing power levels until you can’t ride any further.
Rowe says the ramp test is more manageable than the 20-minute test, so people repeat it more often and therefore have more accurate zones as their training progresses.
Another benefit of the ramp test is that the result depends less on pacing – you simply keep going as long as you can.
On Zwift, after a brief warm-up, the ramp test begins at 100 watts, then increases by 20 watts each minute. At first, it should feel easy, but it will eventually get very hard (how long that takes will depend on how strong you are – the test continues as long you can keep holding the power).
Zwift will then take 75 per cent of the maximum power you reach on the test as your FTP.
No matter which workout you do, Zwift recommends staying seated for the duration of the test effort, because this helps to keep your effort and technique consistent throughout the intervals.
How often should you retest your FTP?
In terms of how often you should be retesting your FTP, Rowe recommends doing so once every six to ten weeks, or at the end of each training block – preferably after an easier few days so that you’re well rested.
You might think it would be useful to test more often, to keep your zones as accurate as possible, but Rowe says that any more often than that and you risk getting bogged down with testing rather than training.
FTP testing tips
Make sure your setup is sorted before you start
Once you hit the test part of the session, you don’t want to pause or take any sort of breaks, because doing so will spoil the data.
With that in mind, it’s vital to ensure your indoor training setup is running as efficiently as possible: make sure you’ve fuelled correctly, have a full water bottle to hand, a fan to keep you cool, and you’ve got some suitably motivational music lined up to last the full duration of the test.
“Maybe” is the correct answer to pacing
When pacing an effort such as a 20-minute power test, it’s very easy to go out too hard and end up finishing with a whimper or vice versa. What you really want to do is ride right on the limit of what you’re capable of for the entire duration of the test – which might leave you wondering how you are supposed to know where that limit is?
British cycling legend Chris Boardman once suggested a method whereby you simply ask yourself, “Is this current effort sustainable for the remaining duration?”. If your answer is ‘yes’, then you’re going too easy, if it’s ‘no’, then you’re going too hard. What you’re looking for is ‘maybe’.
Don’t fret if you’re unhappy with your score
Although hitting huge numbers in the lab/shed/spare room can be exhilarating – and hats off to all those who do it – the final figure isn’t the be all and end all of cycling.
An FTP test isn’t a race – there aren’t any prizes for getting a ‘great’ score, and getting a ‘low’ score doesn’t mean you’ve lost anything either – it’s simply a personal performance benchmark and everyone is different.
Sign up for one of the many training plans available on Zwift and try to focus on the process of self-improvement, rather than the specifics of the raw data. Unless you’re a professional, having fun is what matters, after all. The numbers are just that — numbers.