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.
This has applications in its own right – for example, if you race a 25-mile time trial or you’re racing with a power meter, it can help temper your effort – but it’s more commonly used to set training zones and for measuring improvements (or deteriorations) in fitness.
This makes it useful for cyclists of all types, whether you ride road, gravel or mountain bikes.
FTP is also one of the key figures used to determine all manner of things on Zwift, such as training zones and Zwift racing 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, to give you your all-important FTP figure.
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, roadworks and congestion. Given how downright unpleasant an FTP test can be, there’s nothing worse than having to stop your effort after 15 minutes.
Riding indoors on a turbo trainer removes those variables and enables you to focus on producing your best performance while enjoying the benefits of indoor training.
Why should I take an FTP test?
Before you embark on any kind of training plan, such as those available on Zwift, it’s worth setting a baseline FTP figure for a couple of reasons.
Matt Rowe, of Rowe and King Cycle Coaching and host of the Zwift Power Up Cycling Podcast, says having an accurate figure for your FTP is vital because it’s used to set your power zones.
"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 enable you to know how much progress you’re making throughout the plan.
“Get a couple of weeks under your belt, then get stuck in,” he says. “You’re not going to get a great score [to begin with], but it helps establish where you’re at.”
It's particularly relevant at the start of a new season or when you're about to embark on a winter training plan, 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 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 covered 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, including a 5-minute effort, 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 complete.
Let's take a closer look at both of these options, to help you choose the right one for you.
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 in 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 to set your FTP is to perform one of Zwift's specific FTP workouts. These are available in the Training page.
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, your FTP would be 285 watts.
The second FTP test on Zwift is called the ‘FTP Test (shorter)’.
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.
Classic FTP tests have the advantage of using a reasonably long interval, so test your aerobic capacity very well and can give accurate results.
However, Rowe says they 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.
Zwift Ramp Test
As the name suggests, the Zwift 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. This is useful because getting the pacing wrong on a 20-minute effort can significantly skew your results.
A ramp test is particularly useful if you're using a smart trainer because the trainer will automatically control the resistance for each power interval – so you can focus solely on pedalling.
On Zwift, after a brief warm-up, the ramp test begins at 100 watts, then increases by 20 watts each minute until you can no longer pedal.
At first, it should feel easy, but it will soon get very hard (exactly how long that takes will depend on how strong you are – the test continues as long you can keep holding the power).
Once you can go no further and stop pedalling, Zwift will automatically shift the resistance into a gentle warm-down, then take 75 per cent of the maximum power you reached during the ramp portion as your new 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.
Zwift Ramp Test Lite
Zwift recently added a variation on the ramp test designed for lightweight or more inexperienced cyclists, whose FTP value is likely to be lower.
The goal of the test is essentially the same – you simply keep going at ever-increasing power intervals until exhaustion – but the starting power level is lower and the ramp-up in power increases at smaller jumps.
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 10 weeks, or at the end of each training block – preferably after an easier few days so 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 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 Zwift 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 some suitably motivating music lined up that will 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/pain cave 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.
