Suunto FTP: the watch's 20-minute test, where the number goes, and how to keep it current

How the Suunto FTP test works

Install the FTP test sports app from the SuuntoPlus Store in the Suunto app, start a ride with it, and the watch runs the protocol: 15 minutes of warm-up, a prompt to get ready, then 20 minutes as hard as you can hold at constant power, with time left and power on screen [Suunto Fitness Tests].

Suunto describes the goal of the test as finding the highest average power you can maintain for one hour, and says that power sits close to the anaerobic threshold, which is why it can define your cycling zones [Suunto Fitness Tests]. At the end of the 20 minutes the watch gives you an estimation of your functional threshold power. Suunto notes you can add extra warm-up before the protocol starts.

The test needs power on the watch. Power zones on a Suunto require a compatible power meter, a third-party sensor that measures your effort in watts and transmits it to the watch, and they are available in all Cycling, Indoor Cycling and Mountain Biking modes [Suunto Power Zones]. Without a paired meter there is no power to average and no FTP to estimate.

Treat the result as a field estimate, because that is what a 20-minute test is. In a study that took 95% of 20-minute time-trial power as FTP, the number tracked lactate threshold closely across 20 male cyclists, with a correlation of 0.95 [Valenzuela et al. 2018]. The same study found FTP ran about 6.5% below lactate threshold in the recreational riders, and close to it in the trained ones. A test result is a sound anchor, not a measurement to the watt.

Where the number goes: power zones live on the watch

Nowhere automatic. Suunto's instruction is to set the test result as your zone 4/5 limit in the cycling power zones in the watch's intensity zone settings [Suunto Fitness Tests], and Suunto states that pace and power zones can only be adjusted in the watch, not in the Suunto app [Suunto Power Zones in App].

The path is Settings, Training, Intensity zones, Advanced zones, where cycling and running power zones are set separately [Suunto Power Zones]. Power zones work like heart-rate zones with one difference: there is no maximum power value. FTP becomes the upper limit of zone 4, and the other boundaries are yours to place. To get real-time zone guidance on a ride, select Power as the intensity target in the Options menu before you start.

That design has a cost a cyclist should see clearly. The FTP on your wrist is a number you typed in on the day you tested. It does not move when you get fitter in March or lose fitness over a two-week holiday. Every zone boundary below it was set by hand at the same moment, so a 15-watt drift in real threshold leaves every boundary wrong until the next test and the next round of typing.

A 20-minute maximal effort is not something to repeat every fortnight, so between tests the zones are a snapshot. That is acceptable for an easy ride judged by feel and a problem for a threshold session, where 15 watts is the difference between work you can repeat and work that ends the set early.

No power meter: ZoneSense and heart rate

Without power there is no Suunto FTP, but there is ZoneSense. It reads beat-to-beat heart-rate variability from a chest belt and shows your intensity as green, yellow or red in real time, with no test and no zone setup [Suunto ZoneSense FAQ]. It answers how hard you are working now, not what your threshold is in watts.

The requirements are specific. ZoneSense needs a heart-rate belt that provides beat-to-beat data; optical sensors on the wrist or arm cannot measure it reliably during exercise [Suunto ZoneSense FAQ]. The first 10 minutes of every workout are not measured, because the index cannot be read accurately while you warm up. Suunto recommends it for steady work and intervals longer than 3 minutes, and recommends cycling power for 1-minute efforts, because ZoneSense needs 2 to 3 minutes at an intensity to show it.

ZoneSense also needs easy rides to calibrate. Its scale is built from your aerobic baseline, measured during easy efforts and updated with each workout [Suunto ZoneSense FAQ]. A rider whose week is all intervals gives it little to anchor on. For a threshold number, the Suunto app can map heart rate to your aerobic and anaerobic thresholds after a step-by-step workout that climbs from easy to maximal, and Suunto lists cycling as a sport where that works.

That gives an HR-only Suunto rider a real route: thresholds in beats per minute instead of watts. A plan built on those numbers prescribes heart-rate ranges, and that is what we do when your rides carry no power. The structured sessions we send to your Suunto as SuuntoPlus Guides then carry bpm ranges rather than watts.

Estimating threshold from ordinary rides, and why it matters on the wrist

Every ride with power adds points to your power curve, the best average you have held for each duration. A model fitted to that curve estimates the same boundary the 20-minute test is aiming at [Jones et al. 2010], and it moves as you ride rather than on the day you test. That is the gap the Suunto test leaves open.

When you connect Suunto, we read the recorded file for every ride from the last six months, second by second, and every new ride after that. From those files we estimate FTP and keep re-estimating it as rides arrive. The estimator needs a starting FTP to work from, so a recent Suunto test result is a good seed rather than wasted effort. After that, a hard 8-minute climb in an ordinary Sunday ride counts as evidence, and the number follows your fitness instead of your test calendar.

It matters more once workouts go to the watch. A SuuntoPlus Guide has no %FTP target; it takes absolute ranges in watts or bpm, plus cadence. So we convert the plan's %FTP targets into watts from your current FTP before the session is sent, and it reaches your watch on the next Suunto app sync. A threshold interval at 95 to 100% of a 260-watt FTP arrives as roughly 247 to 260 watts, and power targets need a power meter paired to the watch.

The flip side is that a stale FTP shows up on your wrist in absolute watts. If the number is 20 watts high, every interval in the Guide is about 20 watts too hard. Keep the zone limits you typed into the watch in step with the FTP the plan uses, so the zone display and the Guide targets agree. Why apps disagree on FTP, and when a test still beats a power-curve estimate, are separate questions with their own guides in the FTP-without-a-test cluster.

Quick answers

Sources cited in this guide

1. 01
   Suunto Fitness Tests. Test your fitness with Suunto. Suunto.
2. 02
   Suunto Power Zones. Power zones - How do I get started?. Suunto Support.
3. 03
   Suunto Power Zones in App. Can I set pace and power zones in Suunto app?. Suunto Support.
4. 04
   Suunto ZoneSense FAQ. Suunto ZoneSense FAQ. Suunto.
5. 05
   Valenzuela et al. 2018. Is the Functional Threshold Power a Valid Surrogate of the Lactate Threshold?. International Journal of Sports Physiology and Performance.
6. 06
   Jones et al. 2010. Critical power: implications for determination of VO2max and exercise tolerance. Medicine & Science in Sports & Exercise.

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