Garmin has today announced the release of a chest strap heart rate monitor that’s designed for women. The Garmin HRM-Fit clips to the underband so you can wear it with your favorite running bra.

It’s an important development because electrocardiogram (ECG) chest strap heart rate monitors are much more accurate than the optical wrist monitors found in even the best sports watches, but wearing one with a sports bra is a less-than-ideal arrangement. Wearing two tight bands around the ribcage is a recipe for friction and discomfort. “Whichever way I tried it was annoying,” says ultra runner Rhalou Allerhand about her attempts to wear a chest strap.

While there are sports bras that have built-in connections for ECG heart rate monitors, they’re few and far between. MyZone sells a sports bra that’s compatible with several of its HRMs, but the bra only offers medium support and comes in basic sizes (S-XL) with no adjustability to the shoulder straps. A heart rate monitor that works with any sports bra means you can prioritize getting the right fit.

The Garmin HRM-Fit uses three anchor points to clip onto the underband of any medium- or high-support bra, and transmits your heart rate data to the device of your choice, whether that’s a running watch, cycling computer or a connected cardio machine such as a treadmill or spin bike. There’s no limit to the number of ANT connections, and it can have three Bluetooth connections.

The Garmin HRM-Fit can also measure your heart rate variability, which can indicate if you’re getting ill or overtraining. The monitor tracks running dynamics like cadence and vertical oscillation, as well as tracking running pace and distance, on indoor as well as outdoor runs.

While we haven’t tested this HRM yet, Coach’s senior writer Nick Harris-Fry found the Garmin HRM Pro Plus to be accurate at tracking heart rate and liked the extra running stats tracked, although as with the HRM-Fit these extra stats only work with a compatible Garmin watch.

The HRM-Fit has a 3ATM waterproof rating so it can be used for swimming, with the device storing your data and sending it to compatible devices afterward. 

Garmin says the coin battery will last a year of daily use and you won’t need a screwdriver to change it, it opens with a coin.

The HRM-Fit has a suggested retail price of $149.99 in the US and £139.99 in the UK. That’s a little more expensive than Garmin’s HRM Pro Plus ($129.99 / £119.99), and quite a lot more than most other HRMs on the market. 

If you’re looking for a cheaper alternative that’s almost as accurate and won’t argue with your sports bra, consider the armband-style optical monitors worn on the upper arm such as the Coros Heart Rate Monitor, which features in Coach’s recommendations of the best heart rate monitors.

The combination of value and accuracy makes the 4iiii Viiiiva one of the best heart rate monitors, and it goes above and beyond with a clever bridging feature, which transmits ANT+ signals from other devices through a Bluetooth connection.

While its battery life is subpar compared with newer devices, the 4iiii Viiiiva is still worth considering as one of the best cheap heart rate monitors, even if you don’t need the bridging feature.

4iiii Viiiiva Heart Rate Monitor: Price And Availability

The 4iiii Viiiiva originally launched in 2012 and it is testament to the quality of the monitor that you can still buy it today. The price has dropped in that time and the list price of the 4iiii Viiiiva is now $49.99/£49.99.

How I Tested This Heart Rate Monitor

I have been wearing the 4iiii Viiiiva to track my workouts for several weeks, either by itself or at the same time as wearing the Polar H10 chest strap to check the Viiiiva’s accuracy. I have used it mostly for running, along with a couple of strength sessions.

Design

The 4iiii Viiiiva is a lightweight sensor with a plastic main unit that clips into an adjustable fabric strap, with the pod acting as the fastener for the strap. The sensor uses a CR2032 battery and connects to other devices through both Bluetooth and ANT+. It can only support one Bluetooth connection at a time, whereas many heart rate straps can now support two or three.

Once the sensor is clipped into place it’s easy to pair it to another device, though you don’t get any sound or light signal from the pod itself to indicate it’s connected. The strap can be adjusted from 23in to 52in (57-132cm) and I found once you set the desired length it stays in place reliably and comfortably during long workouts.

The Viiiiva has an IPX7 waterproof rating and can be used to track your heart rate during swimming since it is waterproof to depths of 3m and can store workout data in its internal memory to download later. 

The internal storage can log up to 65 hours of heart rate data in .fit files you can download from the partner app. If you connect other sensors like power meters to the Viiiiva it will record that data too (though this reduces the number of hours it can store), which makes it a handy back-up in case your watch or bike computer crashes or runs out of battery during a workout.

Sports Performance

For all its clever tricks the 4iiii Viiiiva wouldn’t be much use if it wasn’t an accurate heart rate monitor, so I’m happy to report it has been flawless throughout my testing. It reliably logged the same heart rate as the Polar H10, which I have found to be the most accurate HRM available through years of testing.

I did several hard interval runs wearing both the 4iiii Viiiiva and the Polar H10 connected to different watches. Both during the sessions and when looking at the heart rate graph afterward, I did not see any differences in the readings of the two HRMs.

During the weeks I used the 4iiii Viiiiva I was able to link it to a variety of watches and apps easily, though the fact it only connects to one Bluetooth device at a time meant I had to disconnect it from one to link it to another. It also means if you’re using the Viiiiva with a Bluetooth-only sports watch and Zwift on a Bluetooth-only device at the same time, only the watch or Zwift can show your heart rate.

ANT+ Bridging Feature

While ANT+ bridging is not a feature I need, it’s something that will be invaluable to some and it’s the chief reason to choose the 4iiii Viiiiva over other heart rate monitors.

To use the feature, connect the 4iiii Viiiiva to the partner app, link ANT+ devices to the heart rate monitor in there and then broadcast to an external device. 

When the 4iiii Viiiiva originally launched, its ability to link ANT+ devices to Bluetooth ones was a much bigger deal. Since then Bluetooth connectivity has become a standard feature on sports sensors.

However, the bridging feature still has its uses, notably for anyone with an older sensor or indoor bike trainer that uses ANT+ only. One other use for the bridging feature is that it can bundle several ANT+ signals up into one Bluetooth signal, which is useful when connecting to Zwift or other apps on a device that can handle only two Bluetooth signals, such as Apple TV.

Battery Life

4iiii says the Viiiiva will last up to 160 hours on one battery, which is significantly less than most HRMs that use coin batteries. The Polar H10 lasts 400 hours on a coin battery, for example, and the Wahoo TICKR lasts 500.

I found the battery drained faster than this 160-hour estimate. You can see the battery life of your device in the partner app and mine has dropped to 64% after around 30-40 hours of use.

Is The 4iiii Viiiiva Worth It?

The 4iiii Viiiiva is an accurate heart rate monitor at a great price and if you have a use for the bridging feature then buy it. If not, you can get accurate heart rate monitors for less, such as the Coospo H9Z, which has a rechargeable battery and can handle two Bluetooth connections at once, though it can’t store workouts or track swimming.

If you upgrade to more expensive models such as the Polar H10 and Garmin HRM-Pro Plus you get longer battery life and more comfortable straps, and some extra features like running technique stats on the Garmin, but you don’t get a more accurate device for your money.

The best heart rate monitors don’t need to be expensive and, at first glance, I thought this might be the case for the Kalenji Dual HRM from Decathlon. It’s a mainly accurate tracker that costs significantly less than the top chest straps, such as the Polar H10 and Garmin HRM-Pro Plus.

However, in my testing I found the Kalenji HRM delivered more errors than other chest straps. It also lacks features available on pricier picks, like swim tracking and a rechargeable battery. I think it’s worth paying extra for a more reliable experience: The best cheap heart rate monitor I’ve tested so far is the Coospo H9Z, which is only a little more expensive than the Kalenji.

Kalenji Dual HRM: Price And Availability

The Kalenji Dual HRM has been available for several years and costs £34.99 in the UK. It is not currently available on Decathlon’s US website, but costs CA$55 in Canada. 

How I Tested This Heart Rate Monitor

I used the Kalenji Dual to track a variety of runs over a three-week period, including hard sessions on a treadmill and outside, as well as an indoor strength workout. For the most part, I wore it at the same time as a Polar H10 HRM to compare the results, wearing both around my chest. I also wore the Kalenji Dual by itself for a few runs.

Design

The Kalenji Dual has a stretchy fabric belt with a sensor strip on the inside that you moisten before wearing. There is a plastic pod that clips into the front of the belt, powered by a CR2032 battery (included) that needs replacing when it runs out, as opposed to the rechargeable batteries that are becoming more common on chest straps.

You can adjust the length and there is a hook clasp to secure the belt around your chest. I found the belt stayed in place well during long, sweaty activities, though it’s more scratchy and noticeable than other belts such as the Polar H9 and H10. The Kalenji Dual connects to external devices via ANT+ and Bluetooth 4.0 and I was able to link it up easily with three different watches, an iPad and my phone at various points during my testing.

There is no internal memory on the Kalenji Dual so it can’t record workouts; it just broadcasts your heart rate to external devices and apps. It has a 1ATM water-resistance rating, so it’s waterproof to depths of 10m. It isn’t suitable for swimming because it’s unable to store any data tracked in the water to send to a watch later.

Sports Performance

Almost all fitness trackers and sports watches now have a built-in optical heart rate monitor, so the only reason to use a chest strap is because they are more accurate than optical sensors, or because you don’t use a watch or tracker. 

With that in mind, I have a high standard for the accuracy of chest straps. They need to be right 99% of the time to be worthwhile, in my opinion, since they are an extra cost and can be annoying to use. The Kalenji Dual heart rate monitor was spot-on in its tracking most of the time, matching a Polar H10 chest strap beat for beat in most workouts. However, “most” is the key word because I had some problems with it. 

One problem was connectivity. When I linked it to Zwift on an iPad the connection didn’t seem stable and my heart rate readings on screen leapt about, even though the Dual was sending more accurate data to my watch. The bigger problem was significant accuracy errors. During one track workout in particular the Kalenji Dual dropped out entirely during a rep, and in the next rep it was jumping up and down incorrectly. It also spiked incorrectly in the first kilometer of the workout, when I was warming up.

I’ve seen other spikes in runs too. While it was mostly accurate, and was perfect during an indoor intervals session, I’d be less willing to rely on the Kalenji Dual than other chest straps when doing training based on heart rate.

Battery Life

Decathlon doesn’t list the battery life of the Kalenji Dual, but since it uses a replaceable coin battery I’d expect it to last for several months without needing replacing. To save battery life, it’s best to take the sensor out of the belt after use.

In general, coin batteries last much longer than rechargeable ones, though they are more of a pain to change once they run out—though that might be because I never seem to have a CR2032 battery handy when I need one.

Is The Kalenji Dual HRM Worth It?

The Kalenji Dual is the cheapest heart rate monitor I’ve tested and it delivers value as a mostly accurate chest strap that connects easily to a range of devices. However, for me, “mostly accurate” doesn’t cut it, especially when you can get a more accurate chest strap monitor like the Coospo H9Z for just a little more.

And that’s if you just want a no-frills heart rate monitor for activities on land. If you need support for swimming or fancy extra features, like on-board storage for workouts and running technique stats, then the Polar H10 and Garmin HRM-Pro Plus are the best monitors.

My first experience of Coospo came when testing the Coospo H9Z chest strap, which I rate as  an accurate, good- value option that’s one of the best heart rate monitors. I was hoping to be similarly impressed by the Coospo HW9 armband monitor, but while it was mostly OK for accuracy during my testing, it’s wasn’t as foolproof as the likes of the Coros HRM and Polar Verity Sense, which don’t cost that much more and have more features. 

The Coospo HW9 is one of the best cheap heart rate monitors, but if you can stretch to either the Coros or Polar band it’s worth doing, and if you don’t mind using a chest strap you’ll find more accurate and affordable options than the HW9.

Coospo HW9 Armband HRM: Price And Availability

The Coospo HW9 armband launched in June 2023 and costs $59.90 in the US and £49.90 in the UK. That undercuts the price of the Coros HRM ($79/£69) and Polar Verity Sense ($99.95/£86.50). Coospo also has cheaper armbands in its range that I’ve not tested.

How I Tested This Heart Rate Monitor

I’ve used the Coospo HW9 armband to track several runs, as well as a strength workout. To check its accuracy, I also used a Polar H10 chest strap and compared the readings of the two heart rate monitors during and then after the workouts. I have also tested the Coros HRM and Polar Verity Sense armbands.

Design

The Coospo HW9 is a lightweight, square heart rate monitor that sits in a stretchy nylon strap. The sensor has two green LEDs on the back, as well as a color-coded light on the front that shows what heart rate zone you’re working in. The sensor has fewer LEDs than those of the Coros HRM and Polar Verity Sense, which can affect accuracy.

This is a rechargeable monitor with a proprietary cable, and is listed as lasting 35 hours on a charge. You can connect external devices via Bluetooth and ANT+, and two simultaneous Bluetooth connections are supported.

The HW9 has an IP67 water-resistance rating, so it’s waterproof to depths of one meter. However, it’s not designed for swimming and can’t store any data internally, so it’s of no use in the pool. This rating is also lower than other armbands, which are at least 1ATM so can be immersed to depths of 10m.

There is a button on top of the sensor that turns it on, and it buzzes to indicate when it is on. It will also buzz if you take it off your arm without remembering to turn it off by pressing the button.

Sports Performance

The Coospo HW9 monitor is easy to adjust to the right length and comfortable to wear for long workouts. The on/off button and loud, strong buzzing also mean you definitely know when it’s on, so you won’t waste battery by leaving it on after a training session.

Throughout my runs with it I was wearing two watches, one showing the live readings of the HW9 and one the Polar H10, and I could frequently see that the HW9 was a few beats off the highly accurate Polar chest strap. There were no glaring errors, but when testing other armbands, like the Coros HRM, they were more accurate in matching the chest strap throughout runs.

I noticed during a track session that the HW9 lagged behind the reading of a chest strap when starting and finishing intervals. It still logged all the spikes and dips in my heart rate though. Overall, I’d say it was accurate enough to be useful when training by heart rate, just less impressive than other armband HRMs I’ve tested.

The light on the front of the sensor showing your heart rate could be useful, at times, but it’s not that convenient to twist and see it during a workout, especially when lifting weights. You also can’t customize your heart rate zones fully in the partner Heartool app, only change your max heart rate, which changes the other zones but not with real precision. For example, when I performed a lab test to measure my VO2 max more accurately, I also found out that I have a larger zone 2 heart rate than is typical, which I can’t set up on the Coospo monitor.

You can set up an alert when you hit a certain heart rate, track your HR live during workouts, and take heart rate variability measurements in the app. If you did the latter every day at the same time it would be a useful way to check in on the stress on your body, although far less convenient than wearing a watch that takes readings every night.

Battery Life

The Coospo HW9 lasts 35 hours on a charge and has a proprietary charger that attaches magnetically to the back of the sensor. I found that the device drained faster than that listed battery life, though, with the battery percentage at 67% after about seven hours of use. The buzzing helped remind me to turn it off after workouts, though this was less convenient than the Coros HRM, which turns itself on and off automatically when you put it on and take it off.

Is The Coospo HW9 Armband Worth It?

The Coospo HW9 is cheaper than the best heart rate monitors you wear on your arm, and accurate enough, so it does offer value if you want to spend less than you would on the Coros HRM or Polar Verity Sense. 

However, those monitors are not vastly more expensive, and the Polar is often available in sales. Both proved more accurate for me during my testing, and the Coros is more convenient and comfortable, while the Polar has features such as internal storage for workouts and a swimming mode. I’d pay the extra for either of those, but the HW9 will do a solid job at a lower price.

If you don’t mind wearing a chest strap then the Coospo H9Z is better value—both cheaper and more accurate than the HW9.

The Coospo H9Z is one of the best heart rate monitors available, providing accurate tracking and the convenience of a rechargeable battery at a good price. Coospo has cheaper options in its range, which use a coin battery if you prefer that approach, but the H9Z is among the best budget heart rate monitors.

Coospo H9Z HRM: Price And Availability

The Coospo H9Z launched in June 2023 and costs $49.99 in the US and £41 in the UK, though it’s already reduced on Coospo’s US and UK sites. I’d expect it to generally be available for less than its already low RRP. 

How I Tested This Heart Rate Monitor

I’ve been using the Coospo H9Z to track my workouts over the past couple of weeks, most of which have been runs. I’ve used it for three hard interval runs, as well as easy runs and cycles, and compared it with the Coros HRM armband throughout. I’ve also tested the best heart rate monitors from Garmin and Polar, among others.

Design

The Coospo H9Z sensor is a slim rectangle with rounded edges that you clip into the adjustable strap, which is secured via a hook and loop. It has a length of 25in-36in (63.5cm-91cm). The strap is more noticeable and less comfortable than others I’ve tested, such as Polar’s H9 and H10 monitors, but it didn’t significantly annoy me over the course of several long runs.

When you clip the sensor in and put the strap on your chest the Coospo H9Z will beep to indicate it’s on. You can connect it to apps and watches via Bluetooth and ANT+. I found this easy to do with a couple of watches and several apps. It supports two Bluetooth connections at once.

Once you finish your workout you need to take the sensor out of the strap again to stop it beeping at you. This ensures it turns off and saves battery life, which is listed at 50 hours. You recharge the sensor by putting it in the charging cradle provided.

On the front of the sensor is an LED that flashes the color of the heart rate zone that you’re in—you can set this up and adjust the zones using the Coospo Ride app. The sensor also connects to the Heartool app where you can take heart rate variability measurements to monitor stress. You can connect a Coospo bike computer or other cycling sensors and record bike rides with the Coospo Ride app, and track all kinds of live workouts with the Heartool app. 

Having two apps is unnecessary, though most people will probably use neither. Instead, they’ll connect the Coospo H9Z to their preferred app or fitness tracker. The tracker is waterproof with an IP67 rating, but it isn’t suitable for swimming. The rating is also lower than many HR monitors, which offer at least 1ATM, so are waterproof to depths of 10 meters. The tracker also can’t store workouts.

Sports Performance

I’ve used the Coospo H9Z monitor to track a variety of runs, including three interval sessions where my heart rate spiked and dropped quickly. I’m an experienced runner and knew what to expect from my heart rate during these sessions. I also wore the Coros HRM armband during the runs as a way to sense-check the Coospo’s readings.

Overall, I was impressed with the accuracy of the chest strap, which matched the performance I expect from a chest strap. That is to say, there were no errors that I could spot over the course of all my workouts with it.

It paired to watches quickly and reliably and I saw the spikes and troughs in heart rate I’d expect during my runs. It also lined up well with the Coros HRM’s readings, in that the Coospo H9Z showed slightly less lag when tracking intervals, which you’d expect from a chest strap versus an armband relying on optical heart rate readings.

Beyond the accurate heart rate tracking you don’t get a lot from the Coospo H9Z. You can take heart rate variability (HRV) readings in the Heartool app. This can be a good way to track how well recovered your body is, if you do the readings in the same way at the same time each day and look at the recorded stress level. There are no extras, such as running technique stats, which you get from some Wahoo and Garmin devices.

I had the strap covered by a T-shirt during my workouts so the LED showing what heart rate zone I was in wasn’t useful, though it may be handy for indoor HIIT sessions. You can also set a maximum heart rate alert, whereby the sensor will buzz, if you don’t want to push your heart rate too high during a session.

Battery Life

Coospo lists the battery life as 50 hours. So far in my tests, the sensor has matched that and, on occasion, slightly surpassed it. Coin battery-powered straps offer the benefit of lasting several months on a charge, but it’s more annoying to change the battery in them.

Is The Coospo H9Z Heart Rate Monitor Worth It?

The Coospo H9Z is worth its relatively low price, offering reliable tracking and convenience through the long rechargeable battery life. If you need swim tracking or extra features then the best straps, like the Polar H10 or Garmin HRM-Pro Plus, are worth upgrading to. For general tracking, while connected to a watch or app, the Coospo H9Z fits the bill well.

Other good, cheaper options include the Polar H9, which is more expensive than the Coospo H9Z but more comfortable, and uses a coin battery which some users may prefer. The Wahoo Tickr is another reliable monitor that broadcasts HR and offers three simultaneous Bluetooth connections.

Renowned for making some of the best sports watches, Coros has moved into the heart rate monitor market with the launch of the Coros Heart Rate Monitor. This excellent device is one of the best heart rate monitors around, mainly due to how easy it is to use: Just slip it on your arm and it turns itself on, links with your watch and starts tracking.

I found the monitor accurate when compared with a chest strap heart rate monitor in my testing, and the battery life is good enough for weeks of workouts. It’s light on features relative to the Polar Verity Sense, and chest straps are available for less, but the Coros HRM is appealingly simple to use if you prefer to wear an armband.

Coros Heart Rate Monitor Review: Price And Availability

The Coros Heart Rate Monitor launched in the US in July 2023 and costs $79. It’s set to be available in other regions from September 2023. That price means it undercuts the Polar Verity Sense armband heart rate monitor, which is $99.95 in the US and £86.50 in the UK.

• Buy from Coros

Design

This Coros is an optical heart rate monitor that sits in a stretchy adjustable band made from nylon, polyester and spandex. There is a Velcro buckle you can undo to take the band off, though you can also just pull it on and off once it’s set to the right length.

It weighs 0.6oz/19g with the band included and is worn around the biceps, which is a more accurate spot than on the forearm because it’s thicker and moves less during activities. The band length can accommodate arm sizes from 7.09-12.6in (18-32cm).

The band itself can’t store workout data, but instead connects to external devices to broadcast the heart rate that it measures. It doesn’t connect via ANT+, only Bluetooth, but can support up to three Bluetooth connections at once. It connects to external devices from any brand, not just Coros watches.

Although the band is waterproof to 30m, with a 3ATM rating, it doesn’t currently have a swimming mode, though this may be added in the future. You can’t broadcast the heart rate to a watch via Bluetooth while swimming, or at least not reliably, because Bluetooth signals don’t travel well in water.

The band has no buttons, instead turning on automatically when you put it on and then turning itself off when you take it off. The rechargeable battery lasts for 38 hours of active tracking, or up to 80 days in standby mode.

How I Tested This Heart Rate Monitor

I’ve used the Coros Heart Rate Monitor to track all my workouts over the past few weeks. I run almost every day, and have also used it to track bike rides and one yoga session. For the first four runs I did with it I also wore the Polar H10 chest strap monitor connected to another watch, so I could compare the readings of the Coros with the accurate H10.

Sports Performance

The Coros monitor is simple to use. Once it’s set to the right length and linked to your watch—I used three different Garmin watches with it and the set-up was quick and easy—you just pull it on and off for your workouts. The band turns itself on and off reliably and doesn’t dally when it comes to the latter, saving battery life.

In the past I’ve found armband heart rate monitors worn on the biceps accurate—more so than the optical monitors worn on the wrist—and this was the case with the Coros monitor. I did four runs comparing it with the Polar H10 chest strap, including an interval session at the track and a tempo 10K, and it matched the strap beat for beat. 

There was also little lag behind the chest strap’s readings on intervals, which is impressive for an optical monitor even when worn on the arm. Overall, the accuracy was comparable to the Polar Verity Sense armband, and good enough that I felt comfortable using the Coros HRM as my main heart rate monitor instead of a chest strap.

For the most part, I don’t mind wearing a chest strap because I don’t find them uncomfortable, but the benefits of using an armband were obvious when I took it away for a week of trail-running including a 30-mile run. For these runs I wore a backpack with chest straps, and using an armband meant there was no jostling for position between my heart rate chest strap and the backpack straps.

Over the course of that long run, which was almost five hours, the Coros monitor was so comfortable as to be unnoticeable, and it stayed connected to my watch and delivered reliable readings throughout.

Battery Life

When I checked the battery life of the Coros HRM before and after workouts, the drain matched up well with Coros’s listed life of 38 hours of active use. The band will lose more battery life than your workout time because of the way it turns itself on and off, so it’s wise not to put it on until you’re starting your session, but it’s long-lasting enough that you don’t have to stress about juice. 

This battery life gives you more than the 30 hours you get from the Polar Verity Sense, although that has an on/off button so it’s easier to ensure you’re using the battery only when working out with the Polar monitor.

Is The Coros Heart Rate Monitor Worth It?

If you’re just looking for a simple, comfortable and accurate heart rate monitor, the Coros is an excellent choice. The smarter money probably goes towards the more advanced Polar Verity Sense, even at a slightly higher price, because the Polar can store workouts independently of a watch, broadcasts via ANT+ as well as Bluetooth, and has a swimming mode. The Coros has longer battery life and is easier to use.

You will still get slightly more reliable results using one of the best chest straps, like the Polar H9 or H10, and with chest straps like the Garmin HRM-Pro Plus you can also get extra stats like running dynamics. 

If you don’t need those features, however, I found the Coros Heart Rate Monitor the most convenient and comfortable monitor to use. That’s why it has replaced the Polar H10 as my go-to heart rate monitor.

The best heart rate monitors for accuracy are chest straps, but many people find them awkward or uncomfortable during longer activities. Armbands like the Polar Verity Sense are a great alternative since they are more accurate than using a wrist sensor, and the Verity Sense is the best arm strap heart rate monitor I’ve tested.

It’s accurate, connects easily to watches and other devices, and has internal storage so you can track workouts on the Verity Sense and then sync them to the Polar app later. 

Polar Verity Sense Review: Price And Availability

The Polar Verity Sense originally launched in early 2021, with an updated version coming out in May 2023. It costs $99.95 in the US and £86.50 in the UK. Polar has a cheaper armband in its range, the OH1, which costs $59.95/£51.50.

Design

The Polar Verity Sense is a plastic coin-shaped optical heart rate sensor that sits in an adjustable strap, which you can wear on your upper arm or forearm. I’d recommend the upper arm for increased accuracy. You can also wear the sensor in a clip that’s attached to your goggles to track heart rate from your temple during swims.

It’s a small and light sensor—3cm across and weighing 5g without the wristband, and 19g with it. The Verity Sense has a WR50 water-resistance rating (up to depths of 50m) and has 16GB of internal storage, which can record up to 600 hours of workouts.

The Verity Sense connects to external devices via Bluetooth and ANT+. It can connect to two Bluetooth devices at once, and support unlimited ANT+ connections. It has a broadcast range of 150m, which is double the range of the Polar OH1.

There is one button on the top of the sensor that you use to choose the recording mode you want at the start of a session. The first is broadcast HR mode, which is used to connect the Verity Sense to watches and other equipment. The second is recording mode, which you can use to track a workout on the Verity Sense to sync with an app to check your stats later. The last mode is for swimming.

The Polar Verity Sense has up to 30 hours of tracking on a charge, which is 18 hours longer than the Polar OH1. The charger is a small circle the sensor clips into, with a USB plug built in. It’s small and I found it easy to misplace between charges.

A one-size-fits-all fabric strap is supplied with the Verity Sense. This is easy to adjust before you put the strap on, though tricky to do while wearing it. The strap has been adjusted to make it harder for it to flip over accidentally during training sessions. There is a velcro clip to unhook the strap and attach it when in position, but I found it hard to secure one-handed. Instead, I just pulled the elastic strap up my arm without unhooking it.

Polar hasn’t changed much with the 2023 version of the Verity Sense, which adds the ability to use personalized heart rate zones when using the sensor in swimming or recording mode. New red and black bands were launched, made with recycled and bio-based materials, to join the original gray band in the range.

The Verity Sense records your lengths when swimming but otherwise is just a heart rate sensor. This does make it different to something like the Whoop band, which will do things like estimating your readiness to train and track your sleep.

How I Tested This HR Monitor

I’ve tested the original Polar Verity Sense and the updated 2023 model. I run most days, as well as doing workouts like strength and yoga sessions, and indoor cycling. During testing I used the Verity Sense at the same time as a chest strap to compare its accuracy. I have also tested other heart rate armbands like the MyZone MZ-Switch and Polar OH1.

Sports Performance

When you turn the Verity Sense on, you have a few seconds to select the mode you want to use by clicking the button. It defaults to broadcast HR to other devices, so you can ignore this if planning to connect it to a watch, but you need to click it to change it to recording or swimming mode. If you don’t manage to select a mode in time you have to turn the sensor off and on again because you can’t change mode once it’s locked.

In the standalone recording mode the Verity Sense doesn’t crop the recording time to just the actual workout, so unless you start it up just as you begin your training it will record extra time at the start. It’s a useful mode for sports where you don’t want to wear a watch, and you can see your heart rate live using the Polar Beat app, or just sync your workout to the Polar Flow app later to check your stats. 

I mostly used the Verity Sense in broadcast mode, and both versions of the sensors connected easily with a range of watches, as well as my laptop and tablet when using cycling apps like Zwift or Rouvy. I wore it on my upper arm for the most accurate results.

I usually wore another watch connected to a chest strap to check the accuracy of the Verity Sense in real time during workouts, as well as looking at the graphs afterwards. The Verity Sense nearly always matched perfectly to a chest strap’s readings, especially during workouts done at a steady effort level.

In interval sessions with spikes and drops in heart rate the Verity Sense’s readings would lag slightly behind a chest strap, which you would expect from optical readings as opposed to to a chest strap using electrical signals directly from the heart. During a long hills session I saw the Verity Sense’s heart rate readings take a few seconds to catch up at the start of each rep, then they came down more slowly at the end.

I experienced no major errors using the Verity Sense, though, and it’s accurate enough that I’d be happy to use it instead of a chest strap if I did find using the latter annoying. I find chest straps comfortable and the longer battery life from single-use coin batteries they offer is more convenient for me than recharging the Verity Sense. 

I’ve not swum with the Verity Sense yet. To use that mode you need to set the length of the pool you use in the Polar Flow app and attach the sensor to your goggles using the provided clip. The Verity Sense records the lengths you do by noting when you make a turn in the pool. It can link up with the Form swim goggles to show your HR live during swims.

It can’t link to a watch in the water, however, and you can’t download the HR data from the Verity Sense to a swimming workout tracked by a Polar watch in the app after you’ve finished. That’s something you can do with Garmin. Data from one of its chest straps is downloaded to a swimming workout recorded by a Garmin watch once you sync everything with the app.

Battery Life

I tend to do around seven or eight hours training a week, mostly running. The Verity Sense lasted me three weeks on a charge before I’d get antsy and plug it in. That’s because there’s no way to check its battery level apart from charging it, when the LED light on the bottom will change color depending on the battery level.

Going weeks without charging the sensor is convenient, but at the same time means that once a month I’d have to find the charging dock, which was always harder than it should be (my fault, obviously). I found it less convenient to do this than replacing a coin battery in a chest strap once every six months, which is how long the Polar H10 strap lasts me.

Is The Polar Verity Sense Worth It?

If you want an armband heart rate monitor then the Polar Verity Sense is the one to get. It has useful upgrades on the Polar OH1, notably battery life and the improved strap, and is cheaper than the MyZone MZ-Switch, though the latter has the benefit of being used as a chest strap as well.

I’ve no concerns with the accuracy of the Verity Sense, which performs exactly as well as you would expect it would, linking easily to other devices and going weeks on a charge. While it’s expensive, it’s often available in sales. 

If you don’t have a problem with using chest straps, they’re still the best option available in my opinion, since they are more accurate than arm bands and cheaper. Even the best I’ve come across—the Polar H10—costs less than the Verity Sense, and you can get more advanced chest straps that will also track things like running dynamics as well as heart rate.

The main job of a chest strap heart rate monitor (HRM) is simple: to track your heart rate more accurately than optical heart rate monitors like the ones found in fitness trackers. The best heart rate monitors are accurate and sometimes offer more features on top of this tracking.

Unfortunately the Hammerhead HRM has no extra features and during my testing it wasn’t as reliable as other chest straps – in fact its tracking frequently gave wildly incorrect readings.

Hammerhead Heart Rate Monitor Review: Price And Availability

The Hammerhead HRM is available now and costs $64 in the US and £54 in the UK. That’s less than the best chest straps from Polar, Garmin and Wahoo, though those straps offer more features than heart rate tracking. Some straps like the Polar H9 are available for the same price as the Hammerhead.

Design

The Hammerhead HRM is light, with a sensor that weighs 15g. The pod attaches to an all-fabric strap, with two rubber electrodes to detect the ECG signal and track your heart rate. This soft fabric makes the strap comfortable to wear for long periods, and it’s easy to adjust the length using the buckle. The strap uses a hook clasp to secure it in place, and it’s waterproof to 30m and washable. The Hammerhead HRM offers Bluetooth and ANT+ connectivity, and you can connect two devices at once via Bluetooth (ANT+ is unlimited).

How I Tested This Heart Rate Monitor

I have been using the Hammerhead HRM to track all my workouts over the past few weeks, including 15 runs, plus several strength workouts and a yoga session. I connected the strap to three sports watches during that period. I have also tested most of the best heart rate monitors on the market.

Sports Performance

On my first run with the Hammerheard HRM I noticed that it was struggling to pick up my heart rate for the first few minutes. I assumed that I had not wet the strap thoroughly enough before starting and gave it the benefit of the doubt, because after around five minutes it did lock on to what seemed the correct heart rate for the rest of the run.

Unfortunately, this has been a problem on several runs since – no matter how well I prepare the strap before the run by wetting the electrodes. The first five to 10 minutes are a lottery as to what the HRM will read, and it’s usually too high.

I also saw several incorrect drops in my heart rate during workouts while using the Hammerhead, and these sometimes lasted long enough for my Garmin watch to change the classification of the workout, moving it from a tempo to an easy run or similar. This affects the overall training analysis offered by the watch. 

The Hammerhead HRM works well 80-85% of the time. However, the reason I’d wear a chest strap (which is more of a faff than just using the heart rate monitor in a watch) is near-perfect accuracy, and that is what you will get from the best straps like the Polar H10 and H9, or the Garmin HRM-Pro Plus.

If a strap is throwing up errors even just in every third run or cycle, it quickly defeats the point of using it, and the Hammerhead HRM was too unreliable in my testing to make it worthwhile.

Battery Life

The Hammerhead HRM uses a replaceable CR2032 coin battery and the battery life is meant to offer 900+ hours of use, which is a lot. That’s more than double what you get from the Polar H10, for example. Battery life is a strong point, though I noticed the sensor lights flashing occasionally when the strap was not in use, which may drain the battery outside of workouts. 

Is The Hammerhead HRM Worth It?

If you can’t rely on a chest strap being accurate 99% of the time, it becomes superfluous kit, since the only reason to wear them is for greater accuracy than on the optical heart rate monitor on fitness trackers.

As such I’d steer clear of the Hammerhead strap. It’s accurate most of the time, but makes mistakes more frequently than other chest straps. The Polar H9 is around the same price and provides better reliability in my experience, so that’s an easy alternative to recommend.

If you’re happy to spend more, the Garmin HRM-Pro Plus is an accurate strap that also offers running technique stats when linked to a compatible Garmin watch or bike computer.

Polar has long set the standard with its heart rate monitors, and in our experience the H10 is as good, or better, than anything else on the market. The lack of obvious errors leads us to believe it’s the most accurate device available. It’s undoubtedly one of the best heart rate monitors, but unless you find it in a sale the Polar H9 is better value for most people. And, if you’re willing to spend more, the Garmin HRM-Pro Plus offers more advanced features, like running technique metrics.

Polar H10 Review: Price And Availability

The Polar H10 launched in early 2017 and has an RRP of $89.95 in the US and £76.50 in the UK, though you can usually find it in a sale somewhere for less. Polar also has the cheaper H9 strap, which costs $59.95/£51.50. 

Design

There are six strap colour choices with the Polar H10, and two strap size options – M-XXL (67-95cm) and XS-S (58-71cm). You can also buy an extra large strap (82-140cm) by itself.

The pod clips securely into place with two buttons and the strap closes with a clasp. The soft fabric strap has a long smooth section that sits against the skin and contains the electrical sensors. There are also small silicone circles on the strap to help it stay in place during activities, and you can adjust the length easily to get a snug fit.

You can connect to other devices via Bluetooth Smart (two connections) and ANT+ (unlimited connections), as well as 5kHz analog heart rate (unlimited connections). The latter can be useful to connect to cardio machines. The H10 uses a CR2025 coin battery that you can easily replace by taking off the back cover on the pod.

How I Tested This Heart Rate Monitor

I have used the Polar H10 heart rate monitor off and on for several years, testing two H10 straps in that time (I lost the first). I run almost every day and have also used it for cycling, strength workouts and yoga sessions. I have also tested the Polar H9, along with Garmin and Wahoo’s latest sensors.

Sports Performance

The H10 gets a big tick for reliability from us. It’s best to wet the electrical sensor strip before starting a workout – dab some water on or moisten it somehow – to ensure the sensor locks onto your HR from the off. But even if you forget to do that, the H10 is as reliable as straps come, always matching my expectations of where my heart rate should be, and I often use it as the benchmark to test the accuracy of optical heart rate monitors.

It’s also a comfortable strap and I’ve never had any problems with it slipping or rubbing when using it for long runs, and don’t recall any dropouts in connection with whatever watch or treadmill I had the H10 linked to.

The H10 also links to Polar’s apps – Polar Flow and Polar Beat – and you can use it to track workouts with the apps as a standalone device. If you take your phone with you you’ll get a map of your activity, or you can start the workout on your phone then leave it behind and the H10 will track your workout and you can download the data when you come back to your phone. You can only store one workout at a time on the sensor, though.

Even if you don’t intend to use the apps to track workouts it’s worth linking your H10 strap to one of the apps to check for updates and change the settings on the strap. ANT+ connections and the ability to link it to two Bluetooth devices aren’t turned on by default so you need to change the settings to use those features.

The H10 doesn’t offer any of the extra stats you can get from more expensive heart rate monitors. The Garmin HRM-Pro Plus, for instance, offers running technique stats like ground contact time and vertical oscillation, as well as indoor pace and distance – so you can use the strap to track treadmill runs and send your pace to apps such as Zwift.

Battery Life

Polar says the H10 will last for up to 400 hours of workout tracking. I found that it fell short of that and I usually needed to change the battery after six to eight months of use, which would be – as a rough estimate – something like 250 hours. 

It’s still a long time of course and it’s easy to change the CR2025 coin battery using a screwdriver to open up the back of the pod, or your nails if they’re long and strong.

Polar H10 vs Polar H9

The Polar H9 strap launched in January 2020 as a cheaper alternative to the H10. It offers the same accuracy but has a marginally less comfortable strap with a hook closure that doesn’t have the silicone spots for a more secure fit, though I didn’t have problems with the H9 on that front.

You can only connect to one device at a time via Bluetooth with the H9, though it has ANT+ for unlimited connections, and it doesn’t have on board storage for workouts so you need to have your phone with you to track your training sessions.

Given that most people will link the H9 to another device, like a watch, to track workouts the lack of storage isn’t really a problem, nor is the single Bluetooth connection – unless you have a raft of sensors you want to pair that don’t have ANT+.

Overall, the H9 is the smart pick of the Polar pair since it’s cheaper and just as accurate.

Is The Polar H10 Worth It?

Although the Polar H10 is pretty much faultless, the H9 is the better value pick despite being marginally less comfortable. Unless you need the niche extra features on the H10.

Outside of Polar, the best heart rate monitor if you’re happy to spend more is the Garmin HRM-Pro Plus ($129.99/£119.99) because of the extra stats it tracks, though these only benefit people who use a Garmin watch. I’ve found it just as accurate as the H10, and it syncs data to workouts recorded on Garmin watches after swims where the live HR data won’t transmit through the water.

Another option is the Wahoo Tickr X, which also tracks running technique stats and is cheaper than the H10 and the HRM-Pro Plus, at $79.99/£64.99. I haven’t tested the Tickr X but did have the occasional accuracy issue with the cheaper Wahoo Tickr, which doesn’t have the running stats, and I didn’t find it as comfortable as the Polar and Garmin straps.

On the face of it, there might seem little reason to upgrade to the Garmin HRM-Pro Plus over the HRM-Pro. The Pro is already one of the best heart rate monitors and the Plus offers exactly the same features in its software.

However, after using the HRM-Pro for more than a year I can tell you that the hardware upgrade on the Pro Plus is important, because it allows you to change the battery on the monitor without the need for tools. This is not only more convenient but also removes the risk of breaking the monitor while changing the battery, which was a problem for many users.

Garmin HRM-Pro Plus: Price And Availability

The HRM-Pro Plus is available now and costs $129.99 in the US and £119.99 in the UK, which is the same price as the HRM-Pro, though you can usually get the older model for around $100/£100. 

Design

Unlike many heart rate monitors where the sensor clips into the strap, on the HRM-Pro Plus it’s built into it. The strap is fastened via a hook and you can lengthen or shorten it using the buckle. The size range spans from 23.5in (60cm) to 42in (106cm) and you can buy an extender to lengthen this to 56in (142cm).

The sensor differs from the one on the HRM-Pro in two ways. The first is that it has a white rubber covering instead of a yellow one. The second, and more important one, is that you can twist the battery compartment open on the Plus without needing tools, whereas there were four small screws that had to be undone on the Pro.

This was not only a pain – I never had the small screwdriver required to hand – it also risked breaking the HRM Pro, as I eventually did after the third battery change. This didn’t happen to everyone, of course, but it was a hardware flaw that’s evidently remedied by the update.

The HRM-Pro Plus uses a standard CR2032 coin battery and Garmin lists the battery life at 12 months if you train for an hour a day, the same as the HRM Pro. I trained a little more than an hour a day on average and needed to change the battery on the Pro every six to seven months.

You can swim with the HRM-Pro Plus since it has a waterproof rating of 5ATM, but the strap is not as wide or as adhesive as the one on the HRM-Swim monitor, so is more prone to being pushed loose when pushing off from the sides of a pool in particular. The HRM-Pro Plus connects to other devices via both Bluetooth and ANT+ and can store data from your swims internally to transmit to Garmin devices after you finish your workout.

Sports Performance

I run almost every day and I’ve worn the HRM-Pro Plus for all my runs and cycles since it arrived around a month ago. I also used the HRM-Pro for more than a year before it stopped working. The design of both straps makes them comfortable to wear for any length of time and they are easy to keep clean with occasional wipe-downs.

I can’t fault the HRM-Pro Plus’s heart rate accuracy, which hasn’t thrown up any noticeable errors in my time using it. It’s also reliable for finding different devices and connecting to them securely. I often run with two watches linked to the strap and I never have drop-outs.

That’s true of most heart rate monitors, though, and what sets the HRM-Pro Plus apart is the extra metrics it tracks. For runners these include a range of technique stats like ground contact time and vertical oscillation, which you can view live on compatible Garmin watches or see in the Garmin Connect app after your run. The stats are colour-coded so you can easily see what counts as “good”, as well.

The HRM-Pro Plus also measures your running power and transmits it live to compatible Garmin watches, and it can also measure your pace and distance when running indoors. This is calibrated using outdoor runs or on a treadmill and means the HRM-Pro Plus can replace a footpod to send your pace to apps like Zwift.

Both power and indoor pace/distance are new stats measured by the Pro Plus, but both are available on the Pro via a software update, so the only real upgrade here is the new battery compartment.

Is The Garmin HRM-Pro Plus Worth It?

If you already have the HRM-Pro and haven’t broken it with a battery change, then stick with that since there’s no significant update for you here. Similarly, if you find an HRM-Pro at a significant discount it may be worth grabbing instead of the Pro Plus (and then being careful when changing the battery).

Also, if you’re not a Garmin watch user there’s no point in getting the HRM-Pro Plus since most of its stand-out features work only with Garmin watches. Our advice is to look among the best budget heart rate monitors, like the Wahoo TICKR X or Polar H9 or H10, which give accurate heart rate data. 

If you are a Garmin user, particularly a swimmer or triathlete or a runner who wants the advanced stats, then the HRM-Pro Plus is the best heart rate monitor on the market and worth investing in even at its high price. The new indoor running stats are also welcome since you won’t need a footpod now to get accurate pace and distance tracking when on a treadmill.

However, even for Garmin watch users, if you don’t care about the advanced stats and just want live heart rate during activities, then grabbing a cheaper heart rate monitor is the way to go.

A heart rate monitor is now a staple feature on wrist-worn wearables, and these devices’ optical heart rate monitors are reasonably accurate for tracking your heart rate 24 hours a day. However, optical heart rate monitors worn on the wrist during workouts can struggle to get an accurate reading, which is why I always recommend using an external heart rate monitor, usually worn on the chest or upper arm. These can link up with the best running watches and some leading fitness trackers to provide more accurate data.

You’ll find a range of excellent heart rate monitors below, along with a thorough explanation from an expert from Polar, one of the industry leaders, of how the different types of heart rate monitors work and why chest straps are generally the most accurate.

How I Test Heart Rate Monitors

I use each heart rate monitor I test to track my training over a period of two to three weeks. Most of my workouts are runs—I run five or six times a week—with some cycles and strength sessions as well. If testing an armband I’ll check its readings against a chest strap, and when testing chest straps I check them against an armband, though I expect a chest monitor to be more accurate, and sometimes another chest strap. This is usually the Polar H10, which I have found to be highly accurate over long-term use.

The Best Heart Rate Monitors

The H10 is accurate, comfortable and able to connect via Bluetooth, ANT+ and 5kHz, allowing two Bluetooth connections at a time and unlimited ANT+ connections. The battery lasts for up to 400 hours before it needs to be replaced, which means even keen athletes will get through most of a year before having to replace it (a CR2025 replacement battery is widely available and cheap).

It’s also the most comfortable chest strap I’ve worn, a consideration that shouldn’t be underestimated. I found the buckle-like attachment preferable to the usual slip and loop you get on chest straps, and I haven’t had any skin irritation from the H10 while using it for runs almost every day for months.

The downside to the H10 is that most of its features are available on the cheaper Polar H9 strap, which only allows one Bluetooth connection and is a little less comfortable than the H10, though just as accurate. The H10 also lacks the advanced features of straps like Garmin’s HRM-Pro Plus, which tracks running technique stats, as well as your pace and distance when on a treadmill. So, while the H10 remains the gold standard for accuracy and comfort, there is better value to be found elsewhere for most people.

Read more in our Polar H10 review

There are cheaper chest straps in Coospo’s range that offer even more value if you don’t mind using a coin battery, but the convenience of the 50-hour rechargeable battery life of the H9Z means it gets my vote. It’s still excellent value and has proved very accurate during my testing, even during hard interval runs with frequent spikes and dips in HR, and while it’s not the most comfortable strap when compared with the likes of Polar’s H9 and H10, it was fine for long runs.

The functions of the H9Z are, oddly and inconveniently, split between two apps, Coopso Ride and Heartool. You can’t use the Coospo H9Z for swimming and it doesn’t offer extras like workout storage or running technique stats that you do get on some more expensive straps, but for the basics of broadcasting your HR to an app, bike computer or watch it’s an excellent, convenient option.

Read more in our Coospo H9Z Heart Rate Monitor review

The 4iiii Viiiiva is first and foremost a reliably accurate heart rate monitor—it consistently matched the readings from a Polar H10 throughout more than 30 hours of testing. It’s also great value and has internal storage which can hold up to 65 hours of workout data. It disappoints on battery life, though, which is only 160 hours according to 4iiii but drained even faster than that estimate for me.

Its main appeal will be to those who use a lot of sensors that rely on ANT+ connectivity, because the Viiiiva can bridge from ANT+ to Bluetooth. This means if you have multiple ANT+ sensors you want to connect to a device that only uses Bluetooth, the Viiiiva will bridge the gap. While Bluetooth is standard on modern sensors, some older ones only use ANT+, and the bridging feature will prove invaluable in that case. 

Read more in my 4iiii Viiiiva Heart Rate Monitor review

The MZ-Switch can be used to track your heart rate from your wrist, arm or chest. It contains an ECG sensor for measurements on the chest—the most accurate position—plus an optical PPG sensor for tracking from your arm or wrist, which many find more comfortable and convenient than a chest strap.

Wherever you wear it, you’ll be earning MyZone Effort Points (MEPs) during your exercise, and these are earned at a faster rate when you’re working in higher heart rate zones. It’s another way to motivate yourself, particularly during HIIT sessions, and some gym chains have partnered with MyZone to broadcast your heart rate and zone to screens during classes to help you work at the right intensity.

The MZ-Switch also boasts an impressive battery life for such a small, rechargeable device, lasting three to six months (the optical sensor uses more battery than the ECG). It connects easily to any device via ANT+ or Bluetooth, and I found swapping the sensor between the included straps for your chest, wrist and arm a piece of cake.

The only real downside here is the price. It’s more cost-effective to buy a separate arm and chest strap tracker if you don’t plan on using the MyZone app and earning those MEPs.

Read more in our MyZone MZ-Switch review

Polar has two great armband HR trackers in its range, the OH1 and Verity Sense. The Verity Sense is more expensive, but has big advantages over the OH1. The battery life is longer, at 30 hours (vs 12), the Bluetooth range is twice as big at 150m, it has a larger memory for storing workouts, and it’s waterproof to 50m (in contrast to 30m for the OH1). The Verity Sense comes with a clip so you can attach it to your goggles for measurements in the water.

Arm straps offer more accuracy than a wrist-based monitor, and they’re more convenient and comfortable than a chest strap. The Verity Sense slips on easily and in my testing I found it impressively close to a chest strap’s readings in running, strength and cycling sessions, with just a small amount of lag in its readings at the start and end of intervals.

It connects via ANT+ and Bluetooth, and the lights system on the device shows the three training modes available. The first is for when you want to pair it with a device like a watch, the second is for recording a workout directly on the Verity Sense itself to sync to an app later, and the third is a swimming mode.

Read more in our Polar Verity Sense review

The HRM-Pro Plus is Garmin’s top heart rate chest strap, replacing the HRM-Pro in its line-up. The Pro Plus does all the great things the Pro did, including measuring advanced running stats like running power, ground contact time and vertical oscillation, which you can see on compatible Garmin watches live during your runs. It also works in the water and will sync your HR data to the Garmin app once you’ve finished swimming.

There’s nothing to choose between the software of the Pro and Pro Plus. The Pro Plus adds the ability to measure indoor running distance and pace, but this will come to the Pro in an update. However, the key upgrade you get here is a new battery compartment that you can open without using a screwdriver. Not only does this make changing the battery easier than on the Pro, but it also reduces the chances of you breaking the strap, which was a common complaint about the Pro and something I managed to do when using the Pro for an extended period.

Read more in our Garmin HRM-Pro Plus review

The Coros Heart Rate Monitor is not as advanced a device as the Polar Verity Sense in that it only broadcasts via Bluetooth, not ANT+, doesn’t have a swimming mode and can’t store workouts. However, it does a great job of tracking your heart rate accurately and in my experience is the easiest monitor to use, which has made it my go-to option.

This is largely due to the buttonless design. Just slip the Coros monitor on your arm and it turns on and links up to your connected watch. Take it off and it turns itself off again. The battery life is good, at 38 hours of active tracking or 80 days in standby mode, which is slightly longer than the Verity Sense. 

If you’ve no need for extra features and prefer an armband to a chest strap, the Coros Heart Rate Monitor is a convenient option—and cheaper than the Polar Verity Sense.

Read more in my Coros Heart Rate Monitor review

• The Best Budget Heart Rate Monitors

Heart Rate Monitors Buyer’s Guide

To find out more about how chest straps and optical heart rate monitors work, and advice on which is more accurate, we spoke to Polar research center director Jyrki Schroderus and Richard Robinson, senior product manager at Garmin.

What are the pros and cons of a chest strap?

“Comfort is one issue because it results in pressure on your chest area, but it’s very accurate, and it’s very tolerant of disturbances which arise from motion,” says Schroderus. “It’s a hard environment to make the measurement: there’s motion at your chest, there’s lots of sweat too so all the electric characteristics of your skin are changing from dry to sweaty skin. There’s also flapping of the shirt, perhaps because you are riding a bicycle and there’s wind coming against you. 

“So even though the strap looks very simple, there is a lot of engineering behind it and the price point of the device is very low.”

What are the pros and cons of optical heart rate monitors?

“The advantage is that you can make the measurement anywhere where you have skin – your forehead, lower arm, upper arm, anywhere,” says Schroderus. “It’s very handy.

“The measurement is, basically, not as accurate as the chest measurement. There are a couple of reasons for that. First, the location of the sensor could be your lower arm and there is a lot of motion in your arm area. The most catastrophic place for PPG is actually your wrist – it’s a very hostile measurement place. That’s why there are lots of complaints about the quality of the measurement with the wrist devices. We know that and we have lots of people here solving the problem!

“If you put it on the upper arm, it’s almost as good as the ECG-based measurement for heart rate because the motions are not that violent.”

Why are heart rate monitors less accurate in cold conditions, and what can you do to improve accuracy?

“Optical HRM works by detecting blood flow in your wrist,” says Robinson. “When it is cold your body restricts flow to the extremities, ie your hands and feet, and so a sufficient warm-up is needed to increase the blood flow and ensure accurate readings. Also, keeping your hands warm will help the blood flow, so gloves can help in cold weather.

“Chest straps can be challenged initially when the weather is cold and dry as it takes longer for your body to sweat, preventing the conductivity needed for the electrical signals. A simple solution is to dampen the contact points or use an HRM Gel. This increases conductivity and ensures a signal from the start until you have warmed up and are sweating naturally.”

Are optical straps accurate for taking heart rate variability (HRV) measurements?

“With an ECG measurement, you can do HRV measurements in almost any situation,” says Schroderus. “But if you take a PPG measurement, optical heart rate, it’s practically impossible to measure that during motion. If you want to calculate some more advanced parameters, like breathing frequency, you can measure that during your run from your chest, but it’s not possible with the optical heart rate. 

“But if you are at rest, we can measure the PPG PP interval – the separation between successive heartbeats. That’s why we can measure sleep and stress parameters at night with a wrist device.”

Which heart rate monitor is the most accurate?

I’ve tested a lot of chest and optical heart rate monitors from different brands over thousands of miles of running, and I’d say that chest strap monitors are considerably more accurate than the sensors on watches.

While I’ve picked out the Polar H10 as the most accurate chest strap overall—and use it as my HRM running almost every day to compare with other devices—the accuracy of other top chest straps is comparable. As long as you wet the strap to get good conductivity for readings, chest straps are accurate in general, even if the Polar still just about gets my vote as the most reliable overall.

I loved the Oura Ring 2, which I wore from the moment it arrived until I could replace it with the Oura Ring 3. The Oura Ring is the most accurate and useful sleep and recovery tracker I’ve tested, and became the first device whose advice I followed closely with the aim of improving my sleep.

That remains the case with the Oura Ring 3, which is also an excellent sleep and recovery tracker, and takes its place on our list of the best heart rate monitors. However, the gloss has been taken off by a monthly subscription and the new features launched with the third version of the ring, which mostly either underwhelm or are yet to arrive almost six months after the Oura Ring 3 went on sale.

Oura Ring 3 Review: Price And Availability

The Oura Ring 3 is available now on the Oura website. It costs $299 for the silver or black ring, which is around £229 at the time of writing, or $399 (around £305) for the gold and “stealth” versions. On top of this you pay a monthly subscription of $5.99 (around £4.59) to unlock all the analysis in the partner app. 

Before receiving the ring you are sent a sizing kit with plastic rings to help choose the right size. It needs to be snug, but bear in mind your hands will swell up at night and you don’t want it to be uncomfortable. I fell between two sizes, and if you find yourself in the same boat I recommend choosing one that will fit on a couple of fingers. Your fingers change size throughout the day and night, and I found moving it around ensured a better fit at different times.

Buy from Oura | $299

Design

The Oura Ring 3 has an array of new sensors, but felt the same size as the 2 on the finger. The new sensors track your heart rate throughout the day and open up the possibility of heart rate tracking during workouts, although this is one of the new features that has yet to arrive. You can also see your live heart rate in the app, and women can get predictions as to when their period is due (iOS only, arriving on Android in 2022).

Other new sensors monitor blood oxygen saturation (though this has not been enabled yet), and the temperature sensor has had its accuracy improved. Another promised upgrade is an improvement in the accuracy of tracking the stages of your sleep.

I tested the stealth version, which is a matt black colour, after using the shiny black version of the second generation ring. I prefer the look of the stealth ring, but it has been scuffed and shows scratches in a way the black ring never did. If you are worried about that then the black or silver ring may be a better option.

New Features

I only wore the Oura Ring 2 at night, since the daytime tracking it offered was basic and did little to affect the overall sleep and readiness scores the app gave. The Gen3’s new sensors should change that, with daytime heart rate monitoring and workout HR (when it arrives) giving a reason to keep the ring on at all times.

However, after several months with Ring 3 I’ve found that it delivers the same experience as the Ring 2. While that’s good news for sleep and readiness tracking, it means the new features have failed to make an impression.

The daytime heart rate frequently records nothing. The notes in the app suggest that the ring will track your daytime heart rate only when you are relatively still, so there may be long stretches with no data. I envisaged a graph of my heart rate throughout the day showing spikes for workouts and then periods of restorative time that contribute to my overall recovery and readiness scores. Thus far, I’ve just had a graph with gaps, missing workouts entirely and often still failing to register calm periods too. It’s a far cry from the accuracy I’ve come to expect from the Oura Ring.

The app states that it will not log a heart rate reading if it can’t get accurate information, which is an approach I applaud: I’d rather get no data than bad data. But if it struggles to get accurate data most of the time despite being snug on my finger as instructed, then the daytime heart rate feature loses its appeal.

It remains to be seen what will happen with workout heart rate but it’s not encouraging that this feature – meant to arrive before the end of 2021 – has not. Two other features due in 2022 (blood oxygen saturation tracking and improved sleep stages analysis) are also yet to appear.

Sleep And Readiness Tracking

Once you have the ring it takes a couple of weeks to set your baselines for the data it collects, and the data gets more accurate as time goes on. Each day you will be given a sleep score based on a range of factors, such as duration, continuity, time in REM (rapid eye movement) and deep sleep, as well as heart rate variability. This feeds into your readiness score. A higher readiness score means you are primed for intense training sessions, and you’ll be given a higher activity target based on calories, while on days where Oura detects you’ve not recovered well, you’ll get a low readiness score and a low target.

I’m as impressed as ever by the accuracy of the sleep and readiness scores, which pull in a lot of data and present the results in accessible fashion. The data is not infallible, and there are times when I feel the ring is overrating the quality of my sleep, but generally I find it’s accurate enough to be useful in monitoring my recovery during busy training periods, especially when training for a marathon.

The readiness scores mostly tally up with how I feel. When they start to fall, I follow the suggestions for lower levels of activity and earlier bedtimes to help myself recover and feel fresh the next day.

The ring is also remarkable at spotting when I get ill, a feature which worked well on the Oura Ring 2 and which should be even better with the upgraded temperature sensor on the Gen3. Generally, I can see my body temperature and resting heart rate start to rise before more noticeable symptoms hit, which I usually then trace back to the day my toddler came home from nursery with a nasty bug.

It does this better than other wearables, and I happened to have my Covid booster jab while wearing both the Oura Ring 3 and the Whoop 4.0. I had side effects, such as muscle aches, cold symptoms and night sweats, and the Oura quickly spotted my body temperature and heart rate were out of whack and suggested I go into rest mode. For its part, the Whoop said a body temperature rise of 2°C above average was within my normal range.

This knack of spotting when my body is sickening has also been useful during the pandemic. I would never say you can trust a wearable device to diagnose an illness, but during the frequent periods I’ve gone through wondering whether I had Covid, the ring saying that my temperature and other stats were all normal was reassuring.

Battery Life

The battery life is listed at four to seven days, which is odd because there’s no real way to use more or less battery on the Oura as far as I can tell: it just tracks in the background at all times. I have had to charge the ring every four to five days – you get a notification in the app that reminds you to do this before you go to bed.

Is The Oura Ring 3 Worth It?

The Oura Ring 3 is a great sleep and recovery tracker, and you can use its readiness ratings to help you plan your training or your general level of activity each day. Unfortunately, that was true of the Oura Ring 2, and none of the new features that have arrived on the Ring 3 have won me over. I will add that the menstruation prediction feature gets great reviews, but I have been unable to get test data or feedback on that.

Having to pay a subscription to get your data in the app is not a welcome development either. Those who use the free version just get the three scores – Readiness, Sleep, Activity – plus basic info like ring battery and their profile.

I am not a fan of brands locking the info they collect about you behind a paywall, but it’s a particular shame with the Oura Ring because it is already expensive. The main rival in this area is the Whoop 4.0 strap: this has a subscription-only model that is more expensive than the Oura sub, at £20-£30 a month depending on how long a subscription you purchase upfront, but the strap itself is free.

Bearing in mind that when you buy the ring you get six months’ free membership to the Oura app before you have to start paying the subscription, it is smart to hold off buying it until the new features have arrived. Otherwise you could be almost through your free period before they are available.

I still think the Oura Ring 3 is the best tracker of its type, but it is a niche device and many of the areas it covers are now available on sports watches. Garmin’s Body Battery and Polar’s Night Recharge measurements are examples of this. The Oura offers improved accuracy and greater insights than the watches, though it does so at a high price and has little in terms of tracking anything outside your sleep and recovery.

Even for the most committed Peloton fan, the new Heart Rate Band is a tough sell. Whether you prefer an armband or a chest strap, there are many better products available that cost less than this.

The band is easy to use with Peloton’s machines and has a well-thought-out display to show your heart rate zone, but it doesn’t offer ANT+ connectivity and is less accurate than the best heart rate monitors. And we know from our experience of reviewing the Peloton Tread and Peloton Bike, and trialling the new Peloton Guide, that pairing any heart rate monitor to a Peloton machine is easy anyway.

Peloton Heart Rate Band Review: Price And Availability

You can buy the Heart Rate Band from Peloton for £80, which is £50 more than the company’s chest strap heart rate monitor. An alternative of note is the Polar Verity Sense armband, which costs £76.50, offers Bluetooth and ANT+ connectivity, and has a longer battery life than the Peloton band.

Design

The Peloton Heart Rate Band comes with either a small or large armband, with the small band designed for forearms that measure 19cm-27cm and the large for 27cm-34cm. The band is wide and quite thick so it stays in place well, but it’s also hotter and sweatier than the thin band on a product such as Polar’s Verity Sense. 

There is stretch in the band’s strap and I found I could wear the small band on either my forearm or biceps, aided by the small size of the latter. I would advise aiming for a band that also fits on your upper arm because wearing a heart rate band there, rather than on the forearm, results in more accurate readings in my experience.

The sensor is a pod that you slip into the band. Press the top to wake it up and the five-light display will indicate the battery life in bars and flash blue when the band is in pairing mode. Once linked to a Peloton machine or an app it will display the heart rate zone you are in using colour-coded bars.

I found that the Peloton Tread linked up with the band easily, and I could also pair it to third-party apps like Strava. Note it can pair only via Bluetooth, whereas most monitors will connect to devices via Bluetooth and ANT+.

Sports Use

Monitoring your heart rate accurately is a great way to judge effort levels during any kind of exercise, and with Peloton the info is used in the Strive Score that comes up during your workouts. This score works across different workouts well, so you can judge if you’re pushing harder in runs or cycles than you are in HIIT sessions.

I always use a chest strap heart rate monitor for my running to get more accurate tracking that you do from an optical heart rate sensor worn on the wrist. Moving an optical sensor to the forearm or biceps also improves the accuracy. 

The Peloton band was good for accuracy on my forearm or biceps when compared with the readings from a Garmin HRM-Pro chest strap, and the lights on the top make it easy to see what heart rate zone you’re in – though this info is even easier to see on screen if using it with the Tread or Peloton Bike.

However, it did have the odd spike, and sometimes at the start of workouts my heart rate reading from the Peloton band would be too high for the first 10 to 15 minutes, which obviously threw the Strive Score out of whack.

Overall, a chest strap is more accurate and it’s easy to pair one to the Peloton app and machines. However, if you don’t like the feeling of wearing a chest strap, a band worn on the arm is a good option and the Peloton band is comfortable if slightly bulky. Given the Peloton band’s limited connectivity and high price, though, I’d recommend the Polar Verity Sense if you do prefer that style of monitor.

Battery Life

You pop the pod out of the band to charge it in a dedicated cradle, and it lasts 10 hours on a charge. Again this compares unfavourably to other options: the Polar Verity Sense lasts 30 hours on a charge, and heart rate monitors that use watch-style batteries last months before needing their battery replaced.

It is at least easy to monitor the battery level on the Peloton Heart Rate Band thanks to the lights on the top.

Is The Peloton Heart Rate Band Worth It?

No. It offers less connectivity and battery life than chest straps that cost half its price and are more accurate, including Peloton’s own chest strap. Even if you would prefer an armband, the Polar Verity Sense is a better all-round product that costs less. The only feature of note here is the LED display, which is well done but largely unnecessary most of the time.

Opting for a cheap heart rate tracker used to mean compromising on quality, but as the technology has developed and products have proliferated there has been a corresponding rise in accuracy in even the most inexpensive heart rate monitors.

When looking for a bargain it’s still advisable to focus your search on chest straps, which are more likely to be accurate owing to the tracker’s position close to the heart, though armbands worn around the biceps are almost as accurate and can be more comfortable. If you’re prepared to spend a little more, our selection of the best heart rate monitors covers all bases.

The Best Cheap Heart Rate Monitors

The Coospo H9Z just edges out other great budget straps thanks to its long rechargeable battery life. Instead of using standard coin batteries, which are long-lasting but annoying to change when they do run out, the Coospo H9Z is rechargeable and still lasts for 50 hours of use.

It also proved to be reliably accurate during my testing, which included several hard interval runs with my heart rate spiking and dipping quickly. It’s pretty comfortable, if not as good on this front as Polar’s straps in particular, and connects easily to apps and devices via both Bluetooth and ANT+. However—slightly inconveniently—the functions of the H9Z are split between two apps, Coospo Ride and Heartool. 

Read more in my Coospo H9Z Heart Rate Monitor review

Despite originally launching in 2012, the 4iiii Viiiiva is still one the best available, especially for its $50/£50 list price. Over more than 30 hours of testing, the Viiiiva proved as accurate as the Polar H10, and it can store up to 65 hours of workout data so you can use it for swimming, which is not a common feature on cheaper HRMs.

An even less common feature is ANT+ to Bluetooth bridging. It can connect your ANT+ sensors to Bluetooth devices, which means you can continue to use older sensors and pair them to things like tablets and Apple TV more easily. The battery life isn’t very good on the Viiiiva, and it can only connect via one Bluetooth channel at a time, but it’s still a great-value option.

Read more in my 4iiii Viiiiva Heart Rate Monitor review

This budget heart rate monitor from Decathlon’s in-house brand Kalenji is a solid option at a lower price than most others. It connects via Bluetooth and ANT+ and I found it linked easily with a range of devices, including three watches, my phone and a tablet. It’s not the most comfortable strap available, but I found it OK to wear for long runs and other workouts.

During my testing, I had a couple of runs where the heart rate reading was inaccurate, with spikes at the start of runs and a track workout where it glitched for a couple of reps, with the reading jumping and falling for no reason. Overall, the Kalenji Dual was accurate and matched the reading of a Polar H10 the vast majority of the time, and it is indeed cheap, but I’ve found other chest straps more reliable.

Read more in my Kalenji Dual Heart Rate Monitor review

If you’re going for a coin battery-powered HR monitor then the TICKR’s outstanding battery life is attractive, because you’ll get 500 hours of use out of the belt before you’ll need to dig through your cupboards trying to find another battery. The TICKR can link up to three devices at once via Bluetooth, and also has ANT+ connectivity. It’s a great basic monitor that broadcasts accurate heart rate data, but if you want a couple of extra frills the TICKR X is also pretty cheap and able to track running technique stats like vertical oscillation.

I rate the Polar H10 as the best heart rate monitor available, but it’s a little pricy for this buying guide. So it’s fortunate Polar also makes the H9, which I have found to be just as accurate as the H10—it just omits a few of the H10’s features. The main loss is the ability to store workouts internally which means you can’t use it for swimming and transfer the data to a watch or app later. The H9 uses a coin battery and lasts 400 hours before you need to swap that out, and has a more comfortable strap than the other cheap heart rate monitors I’ve tested. 

Armband heart rate monitors are nearly as accurate as chest straps and some find them more comfortable and convenient. The Coospo HW807 uses an optical monitor but using this kind of sensor on the thicker upper arm makes it more accurate than using a wrist-based optical monitor. The HW807 lasts for 20 hours on a charge and connects via both Bluetooth and ANT+.

FAQs

If you want the most accurate heart rate tracking possible while exercising, especially when running or performing a HIIT workout, wear a chest strap that uses an ECG sensor. The next best thing is a strap worn on the forearm or upper arm, which uses an optical PPG sensor. Least accurate is a wrist strap that also uses a PPG sensor.

However, accuracy isn’t the be-all and end-all, and if you exercise for fun then comfort and convenience are just as important. In all likelihood an arm or wrist strap will work just fine for low-intensity activities.

The MyZone MZ-Switch offers the best of all worlds. Wear it on your chest and it uses its ECG sensor, but it will switch to its optical sensor if you use the included arm or wrist straps.

This versatility means you can make the choice between convenience and accuracy every time you exercise. Unless you’re swimming the chest is always the best spot for accuracy, but MyZone suggests that if you’re walking or cycling you can get by with the wrist, and the upper arm will work for running, rowing and weight lifting.

After testing the MZ-Switch in various positions for various workouts, I can say that those recommendations are broadly right, but I’d suggest moving the strap to your chest for running and any kind of HIIT. The arm position provided mostly accurate results compared with a Garmin HRM-Pro chest strap, but the readings lag when you’re spiking your heart rate during an interval, and you’d still get the best accuracy on your chest.

It was one of the better wrist HR monitors I’ve tried during lower-intensity activities like yoga, but I wore it on my upper arm or chest for anything where I was gripping a weight or even my bike’s handlebars. Greater accuracy trumps the marginal extra convenience of wrist vs upper arm for my training.

I was also impressed by the MZ-Switch’s battery life: the sensor will last between three and six months on a single charge (the ECG sensor is less taxing on the battery than the optical one). That’s a serious amount of battery endurance considering the Switch is rechargeable and very small.

It also connects to other devices via both ANT+ and Bluetooth, and I’ve linked it to a range of watches plus my laptop, phone and iPad without any problems. It takes a second to lock on to your heart rate on the chest automatically and then beeps to let you know it’s tracking, while you have to turn it on using its button to use the wrist or arm strap.

See related

• The Best Heart Rate Monitors
• The Best Budget Heart Rate Monitors Under £50

Alongside the hardware, MyZone offers an app built around MyZone Effort Points (MEPs). These are earned based on how hard you work during any type of exercise, with time spent in higher heart rate zones earning you more points compared with the lower ones.

You can follow your real-time effort in the MyZone app, and some gym chains have partnered with MyZone so your heart rate and zone is displayed on a screen during classes. The LED on the MZ-Switch will also flash the colour of the heart rate zone you’re in when using it on the wrist or forearm.

Since everyone’s heart rate zones are personalised to them in the app (based on basic info like age and weight at first, although over time it will be fine-tuned for more accuracy), everyone can earn points at the same rate if they’re making the same relative effort.

The app also contains some guided workouts based on heart rate that you can do with any type of exercise, and there are social elements too in that you can connect with other MyZone users and see their workouts.

The strap will also link to any other app you might be using, like Strava or Fiit, which is a godsend because I did not enjoy using the MyZone app. It’s messy and hard to find what you’re looking for, with social features like your connections or MZ-Chat given prominence over the workout sections. Unless you find MEPs compelling, you might find that you steer clear of the app aside from using it to check the MZ-Switch’s battery life from time to time.

And you would need to find MEPs an attractive proposition indeed to buy the MZ-Switch. At £139.50 it is very expensive. You could combine the Polar Verity Sense armband (£80) with something like the Wahoo TICKR chest strap (£40), save £20 and lose neither accuracy or comfort. I can’t really fault the MZ-Switch, but there’s no reason to invest in this device if you’re comfortable wearing a chest strap and don’t plan on using the MEP system. There are many great straps available for much less that link to everything aside from MyZone.

Buy from MyZone | £139.99

Life in the Whoop world is a relatively simple affair. It’s not here to track your every step or map every workout you do in precise detail. The Whoop strap splits life in two. You’re either putting your body under strain, or you’re recovering from that strain. Put both together and you can ensure the two states balance each other out.

It’s a premise that’s easy to understand and it’s one I like. Each day your activities increase your strain, and each night your sleep helps you to recover. You get a recovery rating out of 100%, and your daily strain is rated out of 21. Your aim, guided by Whoop, is to keep your numbers roughly in line or, if you’re aiming to improve your fitness, carefully overreach with your strain on days your body is ready for it.

The Whoop is a simple device as well. It’s a heart rate tracker you strap to your wrist, forearm or upper arm. There’s no screen. Everything it tracks is beamed to the app, which calculates your overall load. You can swap the strap on the Whoop, and the fabric used is comfortable to wear 24/7 and dries quickly after a shower.

You are meant to wear the Whoop all the time, and when it needs charging (every four to five days in my experience) you attach a small pre-charged power pack that sits on the Whoop itself so you never have to take it off. It’s a really smart and novel idea, though you do have to remember to recharge the power pack itself when you disconnect it from the Whoop. I also had occasional problems with the pack not charging properly so it was dead when I clipped it on.

Your heart rate is key to recording your strain and recovery, and so is your heart rate variability, which many trackers use these days as a general guide to the stress your body is under. Whoop also measures your respiratory rate.

The longer you wear the Whoop strap, the better it knows you and the smarter your feedback gets. You also start to unlock things like the strain coach, which recommends a daily strain target to promote fitness gains, and weekly and monthly assessments that break down your sleep, strain and recovery in a series of graphs and descriptions of how your load increased or decreased.

When you undertake an activity like running, cycling or HIIT, the Whoop can automatically detect it and will give you a dedicated strain rating for that activity, along with a graph showing your heart rate throughout. In my tests the Whoop would sometimes miss my activities, and if this happens you can log it manually in the app to get the strain rating – the Whoop is always recording heart rate and logging strain, so it’s just a case of marking out the time you were exercising.

The sleep tracking on the device provides a lot of useful detail without becoming overwhelming, and showing how what has been tracked is relevant. You are given your time in light, REM and deep sleep along with time awake, plus an efficiency rating based on your overall time in bed vs time asleep. You are even given sleep targets based on whether you want to peak, perform or just get by the next day.

Everything Whoop tracks is rated against its baselines for you. It takes a while to establish these, but that means the device becomes more accurate over time. Eventually it is able to note if your resting heart rate is elevated for a few days or your heart rate variability is lower than usual, both of which can be an indication that your body is under excessive strain or even falling ill.

Your data is engagingly presented in the app, and it’s easy to see key stats like your overall recovery and strain at a glance. There’s also plenty of extra detail on your sleep and general recovery if you do want to spend a bit of time digging into it. You also get weekly and monthly assessments rating your performance in things like strain balance and sleep consistency.

The service Whoop offers is a good one, especially for active people trying to ensure they’re not overdoing it and to line up their harder training sessions on the days when their body is well recovered and primed to handle it.

However, there are flaws. One is that you pay for Whoop with a subscription. A six-month membership is £30 a month (£180). It drops to £24 a month for a year’s commitment (£288), and £18 a month for 18 months (£324). Even though the strap is included, that’s still a hefty ongoing cost.

The bigger problem, however, is that Whoop is dependent on the accuracy of the data collected by the strap, and in my experience this simply isn’t up to scratch.

For starters it’s an optical heart rate monitor, and these are prone to error. I don’t trust even the best optical heart rate monitors to judge my effort during training, based on their performance in comparison with a more accurate chest strap heart rate monitor. The Whoop is far from the best optical heart rate monitor I’ve tried and can’t be connected to an external strap.

When worn on the wrist, it was frequently inaccurate when I was at rest. I compared it with the reading from a chest strap to check, but even by looking at the app and taking my own pulse I could see how far off it was.

Things only got worse during exercise, so I moved the strap to my forearm. Its performance improved, but it was still not close to good enough. I found in this position the Whoop could track my heart rate at rest, but when I was playing with my daughter or doing chores like laundry or gardening it would sometimes log intense activities where my heart rate spiked higher than it would during a hard run, skewing my strain record. This error would happen once or twice a week with the strap on my forearm, and all bets were off when it was on my wrist.

See related 

• The Best Heart Rate Monitors For Workouts 
• How To Calculate Your Heart Rate Zones And What They Mean
• The Best Fitness Trackers

Keen to see if I could extract good data from the Whoop, I moved it up my arm to my biceps muscle. You can buy a dedicated biceps strap, but luckily my lack of muscle mass meant I could use the normal strap on my upper arm. In this position the strap is less comfortable during the day than when worn on the wrist, but I did finally get data that was accurate enough to give me useful feedback that wasn’t tainted by the phantom intense activities it picked up on my forearm or wrist.

However, even on the biceps the Whoop wasn’t infallible, especially during exercise where it occasionally started a workout with a huge inaccurate spike – once again throwing the strain rating out of whack.

Most fitness trackers and sports watches I test read my heart rate far more accurately on the wrist, and during sports I can pair them to a chest strap to get more accurate data. It’s disappointing that Whoop performs so poorly.

In fact, many sports watches offer a similar service, tracking your recovery and overall body stress levels using heart rate variability. Polar and Garmin’s watches are very good on this front. Polar’s sleep and recovery tracking in particular is close to as good as Whoop’s, while Garmin’s Body Battery rating gives a simple snapshot of your overall energy levels rated out of 100.

These watches offer a lot of other useful features too, mainly sports tracking, and don’t require a paid subscription. The upfront cost can be higher than 18 months of Whoop, but you’d expect a flagship sports watch to last much longer.

While the strain and recovery measurements Whoop offers hold promise, there are better ways to spend your money.

Sign up | £30 a month for a six-month subscription

One of the most exciting features to arrive on fitness trackers in the past few years has been the daily rating of your stress levels out of 100. Admittedly for a while we found it mystifying, being unsure how to interpret or act on the information. That was until we chatted to an expert at Firstbeat, who explained that the rating is in part a measure of your heart rate variability using the optical heart rate monitor on the tracker.

Firstbeat is the company behind the algorithms that brands like Garmin use to rate your stress levels, and it also provides in-depth lifestyle assessments (£199) using chest monitors for extra accuracy. We took this test – which involved wearing a monitor for three days – then spoke to Nigel Stockill, performance director at Firstbeat UK, about heart rate variability, what it can tell you about your stress levels, and the limitations of the stress measurements on fitness trackers.

We also spoke to Ben Williams, head of human performance at America’s Cup sailing outfit Ineos Team UK (which are supported by Garmin), about how professional sportspeople use HRV to guide their training and what us amateurs can learn from that.

What Is Heart Rate Variability?

Your heart rate variability (HRV) is tracked by measuring the time between heartbeats – your heart rate rhythm. Even if your heart rate remains pretty constant, your heart rate rhythm can vary, and this shows whether or not your body is in a stressed state.

“When you look at heart rhythm rather than heart rate, we show a slightly different rhythm when we’re in relax and rest mode,” says Stockill. “What we typically see is a very gradual speeding up of our heart rate when we breathe in and a slowing down of our heart rate when we breathe out. This is when our body is undistracted by external or internal forces. It’s in a perfect state for recovery – it’s not busy digesting, or detoxifying alcohol, or dealing with a rapid rise in our cortisol release.”

In the Firstbeat lifestyle assessment these rest periods are marked in green. This shows a higher level of HRV, which indicates the body is relaxed and recovering.

“It’s a sign of less stress. If we go into fight-or-flight mode, it doesn’t mean we’re stressed per se, it just means we’re in that ready state. What happens then is that our body stops the speeding up and slowing down of heart rate and it becomes regular. You’re in a state of readiness – ready to pounce, or run, or whatever.”

The lifestyle assessment plots your HRV over the three-day period. The hope is that you see a good balance of green – where your HRV is high and your body is in a resting mode – and red – where your HRV is low and you’re in a more ready state. If you’re in the red all day and don’t get much green at night, over time you’re going to get more and more run down.

What Causes Low HRV?

You don’t need to feel stressed for your HRV to fall; it’s caused by anything that gets your body going. And the less fit you are, the longer it can take to get back into a resting state.

“It can be just meeting someone,” says Stockill. “It doesn’t mean you’re stressed, but it does mean you spark a little bit of adrenaline, of cortisol. Some people are a lot better at switching that off, whereas others, perhaps because their cardiorespiratory fitness isn’t that good, are not able to regulate that. It tends to be when they’re awake they’re always in red, and they’re only in green in the latter stages of sleep.”

Bodily functions are also key factors, such as digesting food or dealing with alcohol, which both put you into the red zone. This means drinking alcohol in the evening can affect how much you recover during your sleep.

“When the body detects alcohol it sees it as a poison or toxin, so it prioritises detoxifying that alcohol before it can relax. So if it was just one unit you can see that within one hour it detoxifies that, so you can relax quite quickly afterwards. For a lot of people alcohol may be used consciously or subconsciously as a sleep aid, therefore any alcohol that’s still in the system as you go to sleep will delay the onset of green, to the tune of an hour per unit of alcohol in the system.”

Other factors that keep stop you from going into a relaxed state include temperature and exposure to blue light, so staying away from screens last thing before bed and ensuring your bedroom is the right temperature for you are both important.

How Accurate Are HRV Measurements On Fitness Trackers?

One of the key differences with the lifestyle assessment is that an expert talks you through the results and gives you goals to help improve your recovery, rather than the simple stats provided by a wearable. However, perhaps even more important is the difference in accuracy between the chest monitor and a wrist wearable.

“They [wrist-worn trackers] use radial pulse, which isn’t bad compared with five years ago, but it’s obviously not as accurate as [chest straps],” says Stockill. “I wouldn’t be doing any lifestyle interventions based on those [wrist-worn trackers], but they do give you a bit of a guide to time asleep and that kind of thing.

“The difference between being in the red and in the green is so minuscule that if you’re trying to do that from what’s effectively blood flow estimate, you’re always going to be guessing a little bit.”

You can use a wrist-worn tracker to identify trends in your HRV that might highlight how factors like alcohol affect your stress levels, but if it’s something that you’re considering using to shape your lifestyle, a more accurate test is worthwhile. You can get the Firstbeat lifestyle assessment through experts like physios, personal trainers and nutritionists.

How Do Professionals Use HRV In Their Training?

“Knowing these kinds of metrics is very important in elite sport because we push our athletes hard in the quest for performance gains,” says Williams. “We don’t want them to overreach and become overloaded, physically or mentally. Instead we want to make sure we’re pushing them just hard enough so they gain the best training benefit.

“HRV enables us to accurately measure how the team is absorbing the training we give them. It allows us to ensure we periodise recovery in the best way, to make sure we find the sweet spot of training vs recovery for optimal performance gains. We can also use HRV to inform our tapers leading up to competition to ensure we field athletes at a state of readiness with no underlying fatigue that may hinder performance.”

Do You Have Any Tips For Amateurs On How To Use HRV?

“Your HRV is a snapshot of your current autonomic nervous system [which controls many of your body’s mostly unconscious processes] and can change throughout the day,” says Williams. “So my first tip would be to measure each morning at a similar time. This will give you consistency in your measurements.

“Next would be to understand why you are using HRV as a measure. We use it to understand how our athletes are reacting to the stimulus of training and the balance of recovery – nutrition, rest, sleep and so on. Once you know why you personally want to measure it then you can better understand what you will do with the data.

“For exercise it’s a good measure of when is a good time to push and when is good to rest. For example, if your HRV is low, then it probably isn’t a good day to do that hard session because your body is already at an increased rate of stress for one reason or another. Whereas if your HRV is high, today could well be a PB day if you get other variables like strategy and fuelling correct.

“Once you get the hang of using HRV for telling you when to push and when to rest, you can step up your analysis to include how good nutrition and hydration affects your HRV balance.”

The heart rate monitor on the Apple Watch Series 4 is one of the best we’ve tested for accuracy on a wrist wearable, but until now we’ve only been scratching the surface of the device’s potential when it comes to heart health.

That’s because one of the key features of the Series 4 – the ability to take an electrocardiogram (ECG) – wasn’t available outside the USA, where the watch is an FDA-approved medical device. Now, after clinical trials proving its accuracy, the Series 4 has got the CE certification mark for use in the European Economic Area, with the UK and 19 other European nations now set to get the feature, and the ECG app has been added to the watch.

To enable ECG measurements you’ll have to update both your iPhone and Apple Watch (Series 4 only) to the latest software. Then go into the Apple Health app to set it all up and you’ll get a prompt to take your first ECG measurement on the watch, which you do by holding your finger on the digital crown for 30 seconds while keeping your arm still.

You’ll get one of three results from the test – sinus rhythm, AFib or inconclusive. Sinus rhythm means everything is normal, while AFib stands for atrial fibrillation, which means your heartbeat is irregular. If you get that result a few times it’s time to check in with your doctor. Inconclusive could mean that your heart rate was either too low (under 50bpm) or too high (over 100bpm) to take a reading, or that the watch was too loose or your arm too unsteady.

• Apple Watch Series 4 Review – A Big Upgrade
• The Best Heart Rate Monitors
• The Symptoms Of Heart Disease You Shouldn’t Ignore

Doing these checks regularly will provide valuable insight into your heart health, but a better plan of action is to set the watch to take regular ECG measurements when your arm is still throughout the day to automatically check for signs of atrial fibrillation. If it detects AFib on a few occasions, you’ll get a notification.

During testing to get the CE mark the Apple Watch Series 4 was compared with a gold standard 12-lead ECG in clinical trials on around 600 people, and found to be 98.3% accurate in detecting AFib and 99.6% accurate in detecting sinus rhythm in classifiable recordings. Of the readings taken, 87.8% could be classified by the ECG app on the watch.

The Apple Watch is pretty damn accurate then, and even if you just do a couple of tests for the novelty it’s absolutely worth trying the ECG if you do have the latest version of the watch. According to the NHS, atrial fibrillation affects around one million people in the UK. It’s not usually life-threatening, but can be uncomfortable and it’s absolutely something you should see your doctor about to check if treatment is required. Being able to take an ECG so easily with the Apple Watch could be genuinely important in maintaining good heart health, and is almost certainly a sign of things to come in terms of more wearables becoming medically-approved devices.

We’ve taken a look at an early build of PulseOn heart rate monitor – but it’s important to note this isn’t the finished product. The PulseOn is currently on crowdfunding site IndieGoGo and you can pre-order a unit for $169 (around £99). Everyone who does so will receive their PulseOn in September, regardless of how much is raised on IndieGoGo.

Heart Rate Monitoring

A lot of heart rate monitors require a chest strap and these can be inconvenient and cumbersome to wear. The PulseOn aims to make this simpler by placing the sensor on your wrist instead. This also makes it easy to refer to so you can see how hard you’re pushing yourself during your cardio sessions.

The PulseOn is targeted at people who do intensive cardio training. The idea is that having an idea of your working heart rate for the duration of your session, combined with the PulseOn app, will give you a better understanding of how effective your training programme is and provide useful insights such as how long you’ll need to recover. 

The Sensor

The PulseOn consists of a sensor with a heart rate reader on the back. It uses a stretchy fabric strap that feels cheap compared with the straps on the Withings Pulse O2 or Misfit Shine. The sensor itself weighs about 30g, so it’s not too distracting on your wrist, and has a basic LCD screen that we found difficult to read in bright sunlight. You have to squint to see it when you’re out running.

You charge the sensor using a clip attachment which we found difficult to use. It looks simple because it just clamps on to the side of the sensor, but you have to line it up with charging points on the back and it’s easy to miss. A regular microUSB cable then plugs into the clamp for charging from a computer or USB wall adaptor.

There are two buttons on the sensor. The right button cycles through the time, your current heart rate and your previous workout reading. The left button puts it in ‘Sport’ mode to start a new workout. 

PulseOn App

A large part of PulseOn’s appeal is the idea of useful insights generated by the app (otherwise the wrist-based sensor itself just gives you your current heart rate reading and a record of your last workout). Syncing happens over Bluetooth, which means there’s no need to take the sensor off your wrist. 

As well as the estimated number of calories burned during your workout, the app will show you your heart rate readings plotted on a graph as well as the intensity of your workout. To view the graphs you’ll need to rotate your phone horizontally which we found slightly non-intuitive. The app also estimates how long you’ll need to recover as well, helping you figure out your optimum training routine.

Disappointingly, the wrist sensor itself doesn’t calculate speed or distance. You’ll need to use your phone and the PulseOn app in order to get this reading. Likewise, to get a ‘fitness level’ based on your heart rate, you’ll need to have the app turned on with GPS while you run or walk for 20 minutes. For the cost of the sensor, it would have been nice to see a GPS sensor included.

Verdict (current) 

The battery life on the PulseOn build we tested was disappointing – it lasted just a day before needing a charge. PulseOn says it should last ten hours while in Sport mode, so we’re hoping this improves in the final model.

The strap was also poor and we found the charging mechanism fiddly. We did like the array of graphs and information generated by the app and knowing recovering times is genuinely useful.

Getting a heart rate sensor from your wrist is also more convenient than using, say, the Withings Pulse O2, which you have to take off to get a reading from your finger. Being able to get a continuing heart rate reading gives the PulseOn the edge.

We just wish the sensor could detect distance and speed without the need of a companion phone and app. We also hope the app gets some refinements before launch, as we found the Android beta version slow. 

As it stands, the PulseOn has potential. If some of the hardware and software kinks can be ironed out before September it could be a contender.

 6/10

Suunto’s previous watches, the Ambit2 and Ambit2 S, were designed more for triathlon runners and hikers respectively, which may have put off more casual runners who wanted something to cover the basics. The Ambit2 R is Suunto’s response. It trims out many of the superfluous extras and cuts the price to compete with other running watches.

Getting started 

The Ambit2 R looks fairly understated, with a chunky plastic bezel surrounding a digital display. The LCD screen is easy to read in bright sunlight and has a backlight for those early-morning or late-night runs.

You can buy the watch with or without a bundled heart rate strap. It’s a Suunto ANT strap, which works only with Suunto devices, but the watch supports ANT+ so you can use any existing ANT+ strap and save yourself some cash by buying the basic Ambit2 R.

The watch comes in black or white, although the white model has a smaller wristband because Suunto says it expects more women to buy it over the black model. The wrist strap is made of rubber, with a single clasp and two small straps to stop the band flapping about. You’d need to have massive wrists to require the entire length of the black model’s strap, though, so most people should be fine with the white model.

Whichever version you choose, the watch sits fairly flush to your wrist and won’t get in the way if you wear a shirt with cuffs.

How does it work? 

Five buttons around the sides of the screen control the Ambit2 R. When you’re preparing for a run, tapping Start opens the main menu and tapping Next opens the exercise list. As well as a standard Running mode, you have the choice of trail, track, indoor, route and POI (or waypoint) runs, as well as a generic Other Sport mode.

Once you’ve selected an exercise the watch searches for a paired heart rate strap and a footpod if you have one. Pairing an ANT+ strap for the first time can take a few attempts, but once paired the watch should detect the strap in just a few seconds in future. The watch then searches for a GPS signal, which doesn’t take long thanks to clever location pre-caching every time you sync the Ambit2 to your PC.

While you’re on the move you can check your distance, pace, time, heart rate and lap progress, with the watch creating a lap when you press the dedicated Lap button. It even measures altitude and elevation using GPS, which is unusual in a watch at this price. Pressing stop once pauses your workout, so you can resume without losing any data, and pressing the back button stops and saves the run.

Syncing for data 

A USB cable is provided for charging the watch and syncing it with a PC or Mac. It locks on to the watch like a bulldog clip and isn’t likely to pop off accidentally. With GPS disabled you should get over two weeks of use on a single charge, but when using the watch as intended, you’ll get around eight hours on the maximum accuracy. Reducing the accuracy to Good, where the watch updates every five seconds, improves this to 12 hours, and dropping it further to OK should provide up to 25 hours on a single charge, although the GPS updates only once every 60 seconds.

Movescount, Suunto’s online portal, is where you’ll go to upload and analyse your workouts. There’s also a Movescount iOS app, but you can’t pair the Ambit2 R with a smartphone - you have to sync it with a PC to transfer your data to the Movescount website. Once you’ve installed the Moveslink 2 client, the watch syncs automatically every time you connect it to your computer. Having uploaded the data, you can delve into the details, with graphs, route maps and charts revealing every aspect of a particular run. Everything is clearly presented and sensibly arranged, making it easy to track progress over a given period or share your workouts with friends.

Movescount is fairly comprehensive, but Suunto also supports third-party apps, including MapMyFitness and Strava. If you’re used to a particular app or service, there’s a good chance you’ll be able to export your data to it.

It’s through Movescount that you can customise the Ambit2 R even further, downloading “watch apps” to add extra features and modes. There’s a huge number to choose from, and they can provide useful information such as the estimated sunset time, or warn you of an impending storm if the air pressure drops suddenly. It’s a pity some of these features aren’t included by default, but the fact that you can add them at all is great.

The MovesCount website also lets you define your own custom sports. With a little effort you can set up the Ambit2 R for cycling or another activity, even though it’s sold purely as a runner’s watch.

Verdict

On the surface, the Ambit2 R is a comprehensive runner’s watch with a few irritations such as a lack of Bluetooth and smartphone app support. Dig a little deeper, though, and you’ll be surprised at how customisable it can be. With user-created apps, custom activities and extra features that aren’t usually found in a watch at this price, it does just about everything we could want - you just have to explore the Movescount website thoroughly to get the most from it.

Score: 7/10
RRP: £205
Manufacturer: Suuntu

TomTom’s first running watches, the Runner and the MultiSport, were comprehensive gadgets that did their jobs well but required extra accessories if you wanted to track your performance in greater detail. The Runner Cardio improves on the original with an integrated heart rate sensor, saving you the hassle of wearing a chest strap when running, but otherwise it sticks to a tried and tested formula. We wanted to find out if that's enough to make the new model a must buy.

Getting started 

The Cardio looks almost identical to the original Runner, and with good reason – TomTom has made sure existing Runner owners can reuse their original straps with the new model. It’s available in two new colour schemes – red and black, and red and white – to distinguish it from the originals and it bulges out a little further on your wrist to accommodate the new electronics, but not so much that you won’t be able to wear it under a shirt sleeve.

As with the previous model, TomTom includes a proprietary cable to charge and sync the Cardio. You’ll need this to keep the watch topped up with juice, and to transfer your data to a PC or Mac. The main unit pops out of the strap and sits in the cradle when charging. Pulling the unit from the strap takes a little force, so we’re confident that it won’t fall out when you’re on the move. It also helps create a tight seal around your wrist for the heart rate monitor to work properly.

How does it work?

Like the original Runner, the Cardio has a four-way control button for navigating through the menus. It’s very straightforward, requiring just a few taps to find everything you need, and the monotone LCD screen is easy to read without you having to push your nose up to the screen. There’s also a backlight in case you’re out at night or in the early hours.

While you’re gearing up for a run, the watch takes a heart rate reading. The heart rate sensor uses Mio optical technology to measure your pulse by beaming a high-intensity LED on to your wrist. As long as there’s a tight seal around your wrist it’ll find a reading in just a few seconds, with accurate results that matched those of our other HRM-enabled kit.

Once the Cardio has measured your pulse, it scans for GPS satellites. This can take up to a few minutes if you're starting in a new location, but if you set off from a regular start point, the watch remembers and can detect a signal much faster. After a few runs, the watch took less than ten seconds to search for satellites compared with the two minutes at the start.

While running you can tap through several screens that show time, distance travelled, pace, heart rate and lap times. The watch typically lasts for up to nine hours from a full charge when measuring both GPS and heart rate, although with GPS disabled you can squeeze over 24 hours from a single charge.

Syncing your data

After your workout, plugging the watch into a PC or Mac over USB will open the MySports Connect upload agent (assuming you've installed it). From here, your data is uploaded to the MySports website. Log in to your account and you’ll be able to check your performance details, route maps and lifetime progress.

However, although it’s based on the excellent MapMyFitness technology, MySports is overly simplified and won't let you dig down further into your data. What you see is what you get, and unfortunately what you get is rather basic if you’re a serious distance runner. It's worth keeping in mind that the Runner Cardio is designed solely for runners. There are no extra modes for hiking or walking so everything is reported to MySports as a run.

Smartphone apps

If you have an iPhone, you can sync your workout data to the MySports website using the MySports app, bypassing the need for a PC. The watch uses Bluetooth Smart, so you can upload results on the move without having to wait for a Wi-Fi connection. TomTom is still working on its Android app, so anyone who has a smartphone running Google’s operating system will have to connect the watch to a PC or Mac to sync their data.

Verdict

With the Cardio, TomTom has changed very little from the original Runner, but then it didn’t need to - the first version was already tightly focused on running, and this new model does exactly the same job. The addition of the heart rate sensor and a few heart rate-specific information screens complete the package that was arguably lacking last year, making the Runner Cardio an excellent watch for beginner or intermediate runners. At £250 the price is spot on for a runner’s watch with integrated heart rate monitor, and although the MySports website doesn’t provide quite enough detail for dedicated distance runners, for most people it’s everything you could want.

Score: 8/10
RRP: £250
Manufacturer: TomTom

I stopped timing myself during races a couple of years ago after I developed a nasty habit of setting unrealistic minute per kilometre goals. Looking down at my watch at every 1,000m interval of a race to see that I was minutes behind where I wanted to be left me feeling so disheartened I found it hard to keep going. So I decided to run without a watch. Initially I loved being free to enjoy the sensation of racing on perceived exertion alone but in my last few events I’ve tired of not really known how well or badly I’m doing until I get to the end. Especially since in each one I seem to be getting further and further away from setting new PBs.

So when I got an invite to use the long distance at Cannes Triathlon to test the beta version of Polar’s tricked out new heart rate monitor, the V800, I saw it as a good opportunity to reacquaint myself with lots of lovely data. But rather than set targets I couldn’t stick to, I decided I'd monitor how I performed and see what lessons I could take away from it.

As well as the ability to track what your heart is doing during exercise, the V800 contains GPS to feedback on distance covered, and has a triathlon profile that can measure transition durations. It can even tell you how long you need to recover from a session and track non-training activity through use of an accelerometer.

Distance and time are pretty self-explanatory but heart rate training foxes most people, so here’s a simple guide to what it means in terms of exertion. Zone 1 is 50%-60% of your maximum heart rate (MHR), and would be the exercise equivalent of walking. Zone 2 is 60-70% of your MHR, and is the exercise equivalent of jogging. Zone 3 is when you’re working out at 70%-80% of your MHR, the equivalent of running at a moderate pace. Zone 4 is when you’re at 80%-90% of your MHR and is the equivalent of when you're running hard. Zone 5 is 90%+ of your MHR and is the equivalent of sprinting. You can only stay in this zone for a very short amount of time before needing to recover. My resting heart rate (RHR) is 55, and my MHR is 190.

Drink it in

The long distance event starts on Palm Beach, some 2km from the centre of Cannes, and I start recording my sessions as soon as the klaxon sounds. The 2km Mediterranean swim leg is broken down into two laps, with a short beach run between each 1K loop. After a claustrophobic start in churning waters where I’m pinned in between two rather punchy fellows, I find a bit of space, get my rhythm and really begin to enjoy the leg. The water is a balmy 14˚ and so clear I can see the bottom even when 500m out. This means I can check how I’m doing on the V800 by slowing down the stroke of the arm it’s on. 

I run out of the water in 49mins 30sec, with my heart rate having hit 134BPM – so Zone 3 – during the most aggressive parts of the swim, and fumble my way through a transition so long – 7min 26sec – a dictatorship could have been toppled before I finally pedal away from the bike park.

Since arriving in Cannes everyone I'd asked about the bike leg had stories of vicious climbs and hairpins so sharp it sounded as if there was as much chance of you flying off the side of them and gatecrashing some poor French family's BBQ as actually making it round. Oh, and kamikaze drivers who'd make cycling the course feel as if you ridden into a scene from Death Race.

They weren't wrong. After a 5km burn along a wonderfully glassy stretch of motorway, we hit a brutal 7km climb, which pushes my heart rate up to 162BPM and into Zone 4. And there’s little let up after that ­– when I’m not sufffering my way up hills I’m white knuckling it down snaking switchbacks at up to speeds of 50km, dodging oncoming traffic as I go.

My stress levels are further increased when my V800 flashes up a message that I only have one hour of memory left. My fault because I'd recorded a bunch of training rides at home prior to the race and had forgotten to delete them off my watch. At this point I still have at least a couple of hours left of racing, and the thought of doing them without real-time information about heart rate, distance and pace is pretty soul destroying – it’s only taken me half a race to become a born-again data junkie. But the brainboxes who made the device had obviously thought of this because as soon as I clear the message, another one pops up telling me that an old session is about to be deleted to ensure it keeps running during the race.

70km in to the race a man on the French equivalent of a Boris bike overtakes me. I’m on a £5,000 Look road bike that’s been leant to me by the organisers – if I wasn’t beetroot red from exertion, the watching crowds would see shame written in scarlet across my face. I recall a previous scalping at the London Marathon at the hoofs of a man in a horse costume and realise that there must be quite a few failed comedians who are excellent athletes. I really need to get better at endurance events to ensure that a gorilla-suited man on a scooter doesn’t one day beat me.

Step it up

I finish the bike some 3hours 22mins later, and start the run – 16km broken down into 4km laps. It runs along La Croisette – Cannes’s seafront catwalk, famous for the opulent hotels the world’s biggest film stars stay at during the city’s annual film festival. I hammer through the first two laps, spurred on by the supportive crowds yelling, 'bon courage' at me. Such is the energising power of the heartfelt French that I feel completely divorced from the reality of the Nick Hutchings stumbling along at a 5min 40sec kilometre pace.

During the final lap I see a couple of other English-speaking journalists I'd befriended prior to the race. Having people to run with helps me to find another gear and I power over the finish line in 5hours 45mins with my heart rate again in the low 160s. I run straight past the woman handing out medals and don’t stop until I hit the food tent where I shovel down mouthfuls of tepid beef casserole to drown the protein-mad monster threatening to tear up my stomach.

Once I’ve finished my food I find a scenic spot by on the beach to reflect on the race – it’s been eventful and, for the most part, excellent. If you want to do a tri abroad, the short transfer from the UK to Cannes, cinematic charm of the city and hugely varied course make it a great choice. For me, however, the best thing about taking part is how much I’ve learned from the V800 about my in-race performance. For the first time in a long time I now have a load of manageable training targets I can use to make me a faster, more efficient triathlete – the holy grail for racers of all levels.

For more on Polar's V800, go to polar.com. For more on the Cannes Triathlon, go to cannes-international-triathlon.com