Running indoors: Best running watch and wearables for treadmill training

We put five leading wearables to the indoor running test
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While most GPS watches focus on running outdoors, it's easy to forget that millions also spend time on the treadmill as well. Whether just part of a gym routine, escaping the worst of the weather (hot or cold) or just personal preference – finding the best sports watch to track treadmill running isn't easy.

The good news is that most watches and running wearables are equipped to track your time on the treadmill, by swapping the GPS connection to satellites for motion sensors like accelerometers, This tracks the movement of your arms while you run to estimate the distance.

That means if you own a basic Garmin Forerunner 45, or even a more advanced Polar Ignite, Suunto 5 or even Apple Watch, you have the ability to track treadmill sessions.

But naturally, the quality of those algorithms, how the watch learns your gait and cadence, will affect the accuracy.

But which running wearable is the best for treadmill training?

Well, we decided to find that out. We gathered together a range of the best and latest trackers that offer indoor run tracking, took them for multiple treadmill runs to see which one performs best. Here's what we found out.

How we tested (aka the sort-of-science bit)

Before we get into the results, we should explain just how we decided to carry out our testing. For each device, we ran a series of drills designed to closely match the type of sessions you’d normally do on the treadmill. That included:

  • Steady paced run: 5k @ 8-8.30 min/miles
  • Fast run: 3k @ 6-6:30 min/miles
  • Incline run: 2k @ between 8 and 12% incline

We wanted to see how each running watch performed when we mixed up the tempo. We ran at a slower pace, a much faster pace and also hit the incline button for a spot of climbing.

These are all situations that change your form and biomechanics when you’re running. Cadence, arm swing and general bounce are all affected and we wanted to see how the watches’ motion sensors coped with those subtle changes.

We used the treadmill’s own tracking as the benchmark for distance and pace and we also strapped on a Stryd footpod as another comparison point.

Interestingly, the Stryd footpod, which uses accelerometers to track motion and distance from the foot, was virtually spot with its distance reading against the treadmill. So that suggests there’s a good degree of reliability and consistency in the treadmill’s readings.

Suunto 3 Fitness,

Running indoors: Best running watch and wearables for treadmill training

As its name suggests, the Suunto 3 Fitness is a watch designed for all-round fitness so while it tracks indoor running, this device is much more or multi fitness tool than an all-out running watch. As such if you’re looking for a really serious running partner this probably won’t be it.

Read this: Your running watch stats explained

There is a dedicated treadmill mode though and also an optical heart rate monitor to make indoor zone training possible. Unfortunately there’s no option to broadcast your watch data to the treadmill screen so everything has to be monitored on the watch.

The treadmill options include the ability to set heart rate based intensity targets as well as simple duration and distance goals, with vibrating and audio alerts when you hit those targets. You can set time and duration intervals on the watch, including recovery time and there’s automatic lap tracking too. The treadmill is a good place to do controlled interval sessions and so this is a big benefit.

When it comes to accuracy, in our tests, over 5km at steady pace, the Suunto’s distance tracking was marginally short – just 0.03km – and its cadence estimates fell right in the middle of the range of devices on test. That distance shortfall was slightly more significant when we picked up the pace recording 0.08km less than the treadmill and the Stryd footpod over a fast 3km. However, it was on the 2km incline that the Suunto really struggled, adding on 0.25km. That’s a 12% overestimation which is pretty significant.

Despite that, the 3 Fitness was still the most accurate watch on test. This watch also provides many more stats in the post-run review screen in the app than most of the watches we tested. Add to that the fact it’s one of the most comfortable to wear and what you’ve got is a good option for anyone who gets stuck into a range of fitness activities that also includes hitting the treadmill for the occasional spot of cardio.

Garmin Vivoactive 3 Music,

Running indoors: Best running watch and wearables for treadmill training

Another device that’s more all-round fitness tracker on steroids than dedicated running watch, the Vivoactive 3 Music has plenty to commend it. It’s lightweight, nicely designed, comes with optical heart rate and the motivational extra of on-board Spotify playback.

It’s dedicated treadmill mode has customisable screens so you can tweak which stats you’d like to prioritise on the watch itself which is something you can’t do on the other devices here. While the Garmin caters for heart rate zone training and tracks cadence and stride length, there’s sadly no option to broadcast any of that data to the treadmill display.

The Vivoactive’s under-the-roof running skills also stretch to an indoor track mode though we didn’t get the chance to put that to the test.

The Vivoactive needs to be calibrated for indoor tracking and while that might seem like added work, it’s easily done by tapping in the treadmill distance readout after a single run. We were hopeful this would help with accuracy. However, when it came to distance, the Garmin performed worst in all of our test runs.

On the 5km steady it overestimated the distance by more than 0.5km, for the faster 3km it was 0.34km out and on the incline run it generously gave us close to 0.40km extra compared to the treadmill and the Stryd footpod. The fact that it veered from overestimating to underestimating makes it even worse as you can’t even make a calculated adjustment for a consistent misreading. It wasn't a great showing.

Polar Vantage V,

Running indoors: Best running watch and wearables for treadmill training

Polar’s flagship watch is definitely the most serious of the run trackers we tested. It’s also the most expensive. As you’d expect from a top-of-the-range multisport watch, there’s a dedicated treadmill mode and just like the Garmin Vivoactive 3, the data screens can be fully customised to display your top priority stats. Though once again these sadly can’t be broadcast to the treadmill screen.

One of the headline features on the Polar Vantage V is running power tracked from the wrist but it’s important to note that this doesn’t work indoors. Polar’s power estimates are partially based on GPS data which is lost the moment you step inside.

Treadmill runs are tracked using motion sensors, there’s built in optical heart rate and a fantastic cardio load tool that helps monitor your training load and makes recovery time recommendations.

On the run, the Vantage V undertracked both the 5km by 0.11km and this underestimation increased when we picked up the pace for the 3km, clocking 0.33km short against the treadmill and the Stryd footpod. It also over estimated the distance covered on the incline run by close to half a kilometre.

So while it was more accurate than the Garmin in all three tests, it wasn’t quite as on point as the Suunto and it clearly struggled to cope when we moved at a faster clip.

Apple Watch Series 4,

Running indoors: Best running watch and wearables for treadmill training

Undoubtedly the best smartwatch with running skills, the Apple Watch is also easily the most treadmill friendly tracker on this list. Apple embraced indoor running with its NFC-powered GymKit that lets you unlock a suite of treadmill-friendly tricks simply by tapping your timepiece on compatible treadmills.

Read this: Best Apple Watch running apps to try out

Unlike the other watches here, GymKit lets you send data both ways between the treadmill and the watch, plugging gaps in what you see on the treadmill screen and in the data you get on your Apple Watch workout. For example, any elevation info clocked by the treadmill can be sent to the Apple Watch, while heart rate readings from the built-in optical sensor are broadcast to the treadmill display.

The user experience is the best on test too. Wander up to a treadmill, tap your watch and the Workout app is automatically fired up, as is the machine. So there’s no need to open any apps on the watch in order to get going. The only thing you need to do is hit ‘Start’ once you’re ready to begin your session.

However, when it comes to accuracy, even when calibrated by doing a 20 minute outdoor run, the Apple Watch was a long way off the treadmill readings. Over 5km it added 0.28km extra, over 3km at pace it was 0.25km short and on the incline it performed the worst of any of the watches, granting us a whopping 0.85km extra.

Fitbit Charge 3,

Running indoors: Best running watch and wearables for treadmill training

To be fair to the Fitbit Charge 3, this little fitness tracking band is a little bit out of its league against against pricier and more feature-rich devices in this test. But because it comes with a dedicated treadmill mode and a wallet-friendly price tag, we thought we’d throw it in and see how it fared.

For what is essentially a souped up fitness tracker, there are some handy indoor running features. Just like the Suunto 3 Fitness, we really liked that you could set targets for distance, time and calories in treadmill mode. For added accuracy, you can also set your stride length should you know it, though how you find this out is left up to you to decipher.

It’s only when you fire up the app to check your run data post workout, that you realise the Fitbit’s limitations. There’s enough info to satisfy anyone who casually runs for cardio fitness but it lacks the detailed run review stats you get from the other products on test.

Its accuracy leaves a lot to be desired too. It was the second worst performer over the steady 5km, coming up more than half a kilometre short. During the 3km test it simply stopped tracking after 1km. It performed a little better as the second most accurate overall in the incline test, but still overclocked the 2km by 0.36km.

Interestingly, the Fitbit Charge 3 is also the only device on test that doesn’t specifically track cadence, instead it tracks the overall number of steps for the session. A simple sum to work out your strikes per minute showed that this came in consistently as the lowest number on test, often a massive 30 steps per minute lower than the next closest watch.

Best indoor running watch: The verdict

Unless you’re a huge fan of the treadmill, it’s unlikely that you’re going to buy a running watch or run-friendly fitness tracker for its indoor skills alone. However, if you live in a climate that means you often take to treadmill, that should be a consideration.

What our tests suggest is that none of the watches on the market manage a 100% match for the distance measurements offered up by the treadmill or get close to the accuracy of a footpod. And the faster you go, or steeper you go the worse that accuracy gets. In fact if you’re used to sticking the belt at an incline you can guarantee your watch will credit you with more mileage than the running machine.

5km slow Distance Average pace (min/km) Cadence
Treadmill 5.00 5:03 N/A
Garmin Vivoactive 3 5.55 5:15 170
Apple Watch Series 4 5.28 4:57 173
Suunto 3 Fitness 4.97 5:22 174
Polar Vantage V 4.89 5:24 174
Fitbit Charge 3 4.44 5:12 176
Stryd footpod 4.99 5:31 158

5km winner: Suunto 3 Fitness

The winner here is the Suunto 3 Fitness for posting the closest distance tracking to the treadmill. Average pace data though was slower than what was recorded by the treadmill with the Apple Watch Series 4 offering a closer average pace.

3km fast Distance Average pace (min/km) Cadence
Treadmill 3.00 4:20 N/A
Garmin Vivoactive 3 2.66 4:56 160
Apple Watch Series 4 2.75 4:14 181
Suunto 3 Fitness 2.92 4:29 184
Polar Vantage V 2.67 4:58 182
Fitbit Charge 3 1.06 6:15 142
Stryd footpod 3.04 4:26 157

3km winner: Suunto 3 Fitness

Again, it's Suunto's watch that comes out on top in terms recording a distance that was closest to what the treadmill covered. The average pace data was not far off either with the Series 4 posting average pace data almost in line with the treadmill.

2km incline Distance Average pace (min/km) Cadence
Treadmill 2.0 6:37 N/A
Garmin Vivoactive 3 2.39 6:22 144
Apple Watch Series 4 2.85 5:53 158
Suunto3 Fitness 2.27 6:51 170
Polar Vantage V 2.37 6:15 174
Fitbit Charge 3 2.36 6:43 138
Stryd footpod 2.04 7:15 148.5

2km incline winner: Suunto 3 Fitness

It's a hat-trick of wins for the Suunto, which also posted distance data closest to the treadmill data. The Fitbit Charge 3 managed to offer the closest data in terms of average pace.

Final summary

So what’s the best indoor running tracker? Well, if accuracy is your main concern, the Suunto 3 Fitness came up trumps across all three tests. However, you should bear in mind that what you get in accuracy you lose in a watch that’s not very easy to use. The Suunto partner app is also a clunky beast that many people find hard to get along with. So there is a trade off.

If you’re looking for a watch that integrates best with the treadmill – at least all compatible treadmills – then it’s hard to beat the Apple Watch Series 4. The two-way flow of data, the tap-to-start and a reasonable degree of accuracy make this the smartest watch for indoors.

Got any questions about our treadmill test? Let us know in the comments below.

How we test

Kieran Alger


Kieran is a world record-setting runner and one of the UK's most experienced running journalists.

A constant tester of the latest fitness technology, he's always hunting for innovations that can make him run faster, further and generally be in better shape.

Kieran is often found wearing four GPS running watches at once. And to date he's tracked more than 50 marathons, 13 ultras and countless half marathons - including the Marathon Des Sables.

In 2022, he became the first person to run the river Danube from sea to source, a measly 1,830 miles in 66 days. And still had time to test running gear.

Kieran regularly takes running tech to the extremes for Wareable and the likes of Runner's World, Mens Health and Wired.

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