Frontier X review: train with confidence you are not over-straining your heart

I often exercise with an external heart rate monitor paired to my sports watch. As good as wrist based heart rate monitors have become, they are still not on par with chest straps or arm bands when it comes to accuracy. This is particularly the case with high intensity exercises.

It is for this reason Frontier X piqued my interest. It promises physiological metrics that go way beyond your run-of-the-mill heart rate chest strap. The includes things such as Breathing Rate, Step Cadence, Training Load, Body Shock and Heart Rate Variability (HRV).

But what really distinguishes this device from the pack is the advanced heart info – namely ECG, cardiac rhythm and cardiac strain. You’ll get real-time vibration alerts if you cross pre-defined thresholds. This enables you to train safe in the knowledge that what you are doing is not causing undue stress to your heart.

All of this is information that can be very valuable – particularly if you are suffering from existing conditions, recovering from surgery or COVID. Which means Frontier X sits somewhere between a health and sports wearable.

Manufactured by Fourth Frontier, the wearable has been around since late 2020. The company describes it as a “chest-worn device used for athletic training, cardiac rehabilitation and remote monitoring – made to keep you healthy and away from the hospital.” And that’s a pretty accurate description.

With offices in the US, UK and India, Fourth Frontier has lofty ambitions. In July 2021 it raised some $10.5 million in order to scale up its operations. Frontier X typically sells for $499 on the Fourth Frontier website. Use code FFGNW25 at checkout for a 25% discount.

The device promises a lot, but does it deliver? Read on what I’ve made of it after a couple of weeks of use.

Jump to

Design & hardware
Functionality – how to use
Pros & Cons
The bottom line – is Frontier X worth it?

Frontier X review: Design & hardware

  • Looks and feels like a heart rate chest strap
  • Core unit has a small LCD display and set of indicator LEDs
  • Works with smartphone app, on its own and with 3rd party devices
  • Two weeks battery life with typical use

Look & feel

Out of the box Frontier X arrives with the pod that houses the brains of the unit, two elastic chest straps (red and black), a Micro USB cable for charging, two black plastic protective inserts and a quick start guide.

All of this has a one year warranty attached to it, along with a 30 day risk-free trial. The latter is useful if you are not sure about your purchase – it allows you to try the thing out risk free.

It is also worth mentioning – included in the price of the package is a free one-one-one review of your training stats with a Cardiac Exercise Specialist. This is not a medical checkup and is used, instead, to flag up potential issues.

Frontier X review

The device reminds quite a bit of a standard heart rate chest strap. Wearing it is no different. You can use either of the two bands to attach it to your body. The mechanism allows you to tighten or loosen the grip, as needed.

It is a bit fiddly and takes some getting used to but maybe that’s because I’m more used to training with heart rate arm bands than chest straps. I found myself getting frustrated at the beginning, but soon got the hang of it. To ensure accurate readings, you should make sure the band fits snuggly around your chest. But more about that later.

Frontier X review

The core unit snaps onto the strap and you need to press firmly so that it slots into place. You should hear a click. Just make sure to remove the two black plastic protective inserts inside the metallic electrode socket before you first do this. The device should be positioned so that it’s located right in the middle of your chest.

The hold of the strap is very secure and there’s absolutely no danger of it falling off. The build is also pretty pretty solid. I don’t think the device would get damaged easily, even if you accidently drop it (which I did once or twice).

Around your chest everything feels lightweight. The actual measurements of the core unit come in at 73mm x 24mm x 13mm and 25 grams in weight. That’s pretty close to a standard heart rate chest strap.

As far water resistance – the device is IP67 rated which means it is can be submerged down to 1.5 meters. That makes it safe for swimming in the pool.

Frontier X review

There’s a display on-board along with indicator LEDs

On the front of the core unit is a screen which I found to be of limited use. It is a nice feature to have – but it does feel a bit superfluous. That’s because without a mirror in front of you, there’s little chance you will be able to make much use of it. Try reading something that is sitting across your chest – it’s not easy.

Having said that it is useful for knowing what mode the device is in, how much battery life is left, etc. It also spits out an activity summary which you can read when you remove the pod from the strap post exercise.

Frontier X is operated by a single physical button that can be found on the underside of the device. That is also helpful in letting you know if you’ve put it on the right way around. The red button should be facing towards the ground when the strap attached to your chest.

One press of the button switches the unit on. Two presses start and end an activity. You can also use the button to log event markers during exercise.

At the opposite end is a small strip of LEDs. They shine in one of three colours – blue, green and red. This is used as indicators the device is switched on ready to pair, it is paired, it is switching on/off and more. The controls are actually pretty simple and to the point.

Frontier X review


You can use Frontier X in one of three ways during exercise. The default way is by pairing it to the iOS or Android smartphone app and starting and stopping workouts from there. The device uses Bluetooth to communicate with its surroundings so there is no ANT+ support. Or you can use Frontier X on its own and then sync everything to the smartphone afterwards.

The final option is to pair it with 3rd party devices as an external heart rate monitor. This includes those manufactured by Garmin, Polar, Wahoo, Zwift and Peloton. In this mode Frontier X sends out heart rate data to the paired device.

I tend to use a Garmin Forerunner 945 watch for training and had no problems whatsoever pairing it with Frontier X. It was quick to connect and there were hardly any drops during exercise.

Frontier X

Frontier X
Use code FFGNW25 at checkout for a 25% discount

Frontier X

A recent firmware update allows you to connect Frontier X to multiple devices. A maximum of two 3rd party devices are allowed at the same time, in conjunction with the smartphone. You are unlikely to need that many but it is nice to have the option.

You’ll find Fourth Frontier is pretty good at churning out firmware updates regularly. In the past six months an average of one update per month was issued. Each brought improvements and additional functionality in addition to the usual bug fixes.

Battery life

As far as battery life, on a full charge you can expect around a day if Frontier X is used continuously. Which might not sound like a lot. But, most people are likely to use it from time to time – primarily as a chest strap while exercising. Taking that into account, the typical user will only need to reach for a charger once every two weeks.

I used Frontier X for a couple of weeks and think I could have probably gone throughout the whole period without charging. To be on the safe side, I did a quick top-up every 4-5 days. The cable that is used to refuel is a standard Micro USB, so if you lose it there’s no problem with replacing it.

Frontier X review: Functionality

  • Captures heart health info during exercise
  • Can be used as a standard heart rate chest strap, but you get additional insights
  • Detailed physiological metrics in smartphone app & website dashboard
  • Continuous 24 hour ECG recording

Setup & use

The first set-up is fairly standard stuff. Download the Frontier X smartphone app, create an account, answer a few basic questions and pair the device. You’ll notice, once you create a account on your smartphone, the same username and password will automatically allow you to access the web dashboard. This contains more information than the smartphone app so is useful to check-up on.

The first couple of times I used Frontier X in conjunction with the smartphone app to track my exercise rather than a 3rd party device. This is done by attaching the strap to your chest and switching it on via the physical button. The screen will come to life and show you the current time and then a summary of your last workout, along with battery and memory percentages.

Through trial and error I learned that it is best to wet the sensors on the strap as well as your skin where the sensors make contact. Otherwise there might be gaps in data at the outset of your workouts. There is nothing strange about this, most heart rate chest straps work better if you wet their sensors.

Then you need to:

  • click on the Activity tab in the smartphone app
  • choose the type of activity (run, cycle, walk, strength, etc).
  • At this point you have the option of editing alerts. One of these is for Cardiac Strain, the other for Breathing Rate. You can define the upper and lower limit for both. If the threshold is exceeded during exercise, you’ll get a double buzz alerting you.
  • Save and click start. It takes about 20 seconds for the first readings to come through.
Frontier X review app

More about alerts

Fourth Frontier places special importance on breathing rate. The company believes that this metric is just as important as your heart rate during exercise. While that might be up for debate, most would agree on the importance of heart info. And this is where Cardiac Strain comes in.

Medically Cardiac Strain is refered to as ST depression. Fourth Frontier explains that their proprietary metric “measures the amount of Oxygen deprivation experienced by the heart muscles”.

A high value of Cardiac Strain for prolonged periods of time can cause damage to your heart cells. Basically, you should avoid training often with such intensity. That’s because doing this can, in the long term, lead to conditions such as fibrosis or arrhythmias. Hence the usefulness of Frontier X – it buzzes to alert you in real-time if you cross into unhealthy territory.

There’s also a Cardiac Rhythm feature which helps detect any heart rhythm deviations by looking at your ECG. You’ll get a pie chart in the stats after exercise showing how long you were in Blue (Normal Sinus Rhythm), Yellow (Other Rhythm) or Gray zone (Not interprable).

More detail on Cardiac Rhythm can be found in the charts which group the data into 20 second intervals. If there’s a suspicious change detected in Cardiac Rhythm, that 20 second session will be flagged.

I was happy to learn that my training sessions were mostly in the green and yellow (both safe) zones as far as Cardiac Strain. My Cardiac Rhythm readings were also almost entirely in the healthy range. Having had a run-in with COVID-19 twice, most recently two months ago, the knowledge that my heart metrics are in the healthy range while exercising gives me peace of mind.

Real-time summary during workouts, detailed stats post-workout

During workouts you can see real-time physiological stats in the smartphone app. I predominantly used Frontier X for running and walking. For these types of activities metrics include Effort, Strain, Heart Rate, HRV, Training Load, Cadence, Distance and Pace.

You can mark significant events during workouts by single pressing the physical button on the device. For example if you were feeling a particular strain, difficulty breathing or simply starting a new lap. You will be able to see these events later on in the exercise summary charts – they will be flagged up in the form of vertical black lines.

If you don’t want to view real-time stats, you can leave your phone behind while exercising. Simply start and end the session by pressing the button on the device itself. Everything will be stored on the onboard memory.

Post workout allow Frontier X to sync to the smartphone app. This usually takes 2-3 minutes depending on the length of your exercise. Then sink your teeth into the wealth of stats and graphs on various aspects of your workout. When tracking via a smartphone, there’s also a GPS map of your route.

Some of these stats are fairly standard – basically what you’d get from a heart rate chest strap. Others, such as an ECG trace, Cardiac Strain, Cardiac Rhythm and Body Shock are quite unique.

You really can spend a lot of time sifting through all this data. It makes interesting reading because it is not typical of what you’d get with other devices.

In addition to heart health info, I feel Body Shock is also worth a special mention. This metric measures the force against the body while striking the ground. It gives you an indication if your workout technique is likely to cause damage to your knees and other joints. This is charted progressively as you exercise so you can assess whether there is a deterioration in your technique as your workout progresses.

The smartphone app allows you to see detailed charts that cover most physiological metrics. You can switch between tables and even compare them in the “Comparison” view. There’s also an option to view any alerts you may have received during the workout.

I also found the workout summaries to be an interesting read. In plain English you’ll get an assesment of your exercise in addition to recommendations for next time around. This is based on your weekly workout Training Load which is automatically calculated for you.

Using the website dashboard

In addition to the smartphone app, you can also use the website dashboard to review your stats. I actually found the website dashboard to be of more use. Frontier X dishes out a wealth of stats and the large screen format is ideal for sifting through these in detail.

You’ll get everything that is available in the smartphone app but with the ability to zoom in, activate the caliper tool and more.

Here’s are a few screen shots which will give you a better understaing of all of this. This includes a Health Trends sections which charts your progress in time. At the outset this section won’t make much sense, but after a week or two of training trends will start to appear.

Using Frontier X with a 3rd party device

As mentioned, you can also use Frontier X with a 3rd party device. I paired my Garmin Forerunner 945 to it with no issues whatsoever. Simply connect it as you would any other external heart rate chest strap.

The thing to know is that Frontier X is only sending data to the Garmin watch. It is not receiving any data back – such as GPS data.

So the procedure when tracking a run is to commence the activity by double clicking the button on the strap. Wait about 20 seconds for the physiological metrics to start coming in. Then start recording your activity on your Garmin watch as you normally would. When you finish, you’ll need to end the activity both on your Garmin watch and on Frontier X.

Those with an Apple Watch will be happy to know there’s a Frontier X app that allows you to choose your activity type and start and stop it from the watch. Rather usefully, it will also display multiple Frontier X metrics on the watch in real-time. This is something that is not available on Garmin and other watches yet and is on my wish list – the ability to view other physiological metrics in real-time, in addition to heart rate.

Accuracy – sampling rate

The ECG signal on Frontier X is sampled at 125Hz intervals which equates to once every 8 milliseconds. That’s quite good. This is the metric that is used to evaluate your heart health.

The heart rate and heart rate variabilty signal, however, is only captured once every second or two when connected to a third-party watch such as Garmin. If you’re tracking activity from the Frontier X app, then its once every 20 seconds. I’m not sure why this is the case – perhaps to preserve battery life.

I compared the accuracy of Frontier X with a Polar OH1 chest strap coupled with a Garmin watch. The stats were bang on – practically no difference. I did spot, though, that while the maximum heart rate was typically the same or only 1 bpm off, the average heart rate on Frontier X would typically be 2 to 3 bpm lower than on Polar OH1. This is on a 5k run. My guess is that it is probably due to the 20 second wait at the outset, plus the slightly lower sampling rate as compared to a standard heart rate chest strap.

Continuous 24 hour ECG recording

Beyond tracking workouts, you can use Frontier X as an ECG recorder. The special mode is triggered from the smartphone app. This is where the device crosses into purely a health wearable.

Frontier X is a single lead ECG. But it more closely resembles the output from the V5 lead of a medical 12-lead ECG measurement.

On its website Fourth Frontier states the following.

In studies comparing the Frontier X to a Holter Device and 12 Lead ECG, the Frontier X picked up all abnormal heart rhythm changes (arrhythmias) found by Holter and 12-Lead ECG, and adequately measured heart rate and QTc changes.

There is no way for me to confirm the actual accuracy of ECG recordings. But I do have a few devices in my arsenal that can capture ECG – and the waveforms look very similar.

Frontier X ECG streaming

For those that want to share their recording with a doctor or a loved on, Frontier X comes with an option to send remote readings. You’ll get a link which you email to the other person – once they click on it they’ll be able to follow your ECG in real-time. By the way, you get this same option when starting a workout via the smartphone app.

Frontier X review: Pros & Cons

Frontier X has a lot of things going for it. Headlining the Pros side, I would flag up the heart health stats. Cardiac Strain and Cardiac Rhythm. They add a whole new element to your activity tracking.

The functionality works well and alerts you if something is amiss. As mentioned, I found it useful as it gave me peace of mind following two bouts with COVID-19. Beyond that, you might be suffering from heart rate issues that you might not be aware of. The idea of this wearable is to warn you if this is, indeed, the case. It also warns if your breathing rate goes up to much during exercise, as this can be damaging to your lungs.

The other Pros I would include are:

  • the ease of use,
  • excellent battery life,
  • the wealth of physiological stats captured (HRV, Breathing Rate, Body Shock, etc),
  • the simple to use app and web dashboard,
  • the ability to live-stream your metrics,
  • the ability to take long-continuous recordings of your ECG (smartwatches with ECG typically record only 30-60 second segments)

On the Cons side, the wearable is quite pricey – particularly if you compare it to a standard chest strap. The other negative is the sampling frequency of heart rate which is slightly below a standard chest strap connected to a watch. This is unlike ECG which is captured practically continuously.

Also, it would be nice to be able to view, in real-time, more than just heart rate on connected Garmin watches during exercise (via a ConnectIQ app / data field). Frontier X is already transmitting heart rate information, so surely it can be done.

Finally, I really hope that Fourth Frontier come out with an armband instead of a chest band. Those types of devices are much easier to use.

Here’s a nifty little chart put together by Fourth Frontier. It shows how their flagship wearable compares to heart rate monitors, smartwatches with ECG and ECG halter monitors. This gives a good overview on the differences between each.

Frontier X review: The bottom line, is it worth it?

Going into this I thought the Frontier X review would be a short one. After all, how much can you write about a heart rate chest strap? Quite a bit, as I found out.

That’s because Frontier X goes way beyond what any other chest band can do. I’d say it sits somewhere between a sports and a health wearable.

You can use it to supplement the stats that you typically get from your sports watch with additional insights. Is your exercise intensity causing undue strain to your heart and lungs? Can you push harder? Frontier X will give you this type of information.

It will even help prevent injury by measuring the shock your body suffers during each foot-strike. This is in addition to capturing a bunch of other physiological metrics which I found to be useful.

The other aspect of the wearable is its live ECG function. This can be useful if you are recovering from a heart issue or simply want to check on the health of your ticker. The option to allow others to monitor the readings remotely is a nice add-on.

There really is a lot to like about Frontier X and I love using it as a companion to my Garmin watch. I found the stats to be pretty much on par with the Polar OH1 chest strap.

I tend to push myself a lot when exercising and it’s reassuring to know that I am not overdoing it. Frontier X helps me stay in the safe zone. It gives me peace of mind I didn’t have before.

Frontier X

Frontier X
Use code FFGNW25 at checkout for a 25% discount

Frontier X

The question is – is it worth the money? The wearable is quite pricey. Well, that really comes down to – what do you really need?

If you are purely looking for heart rate information – a normal heart rate chest strap is the better option. It costs less and captures heart rate with a higher sampling rate.

But you will be missing out on all the other health information that comes with Frontier X. It is not a medical device, but it adds a whole new addition to your cardio training fitness arsenal. 

Anyone who is looking to train with mild heart conditions, those who are recovering from surgery or COVID might benefit from the device. And anyone else, really, who wants to keep a closer tab on their health. You can never be too safe when it comes to your heart, particularly as you age.

Frontier X typically sells for $499 on the Fourth Frontier website. Use code FFGNW25 at checkout for a 25% discount.

A purchase includes a free Cardiac Exercise Specialist review of your exercise activity. It is not a medical heart checkup – rather it is a consultation to make you aware of any potential issues that might warrant further investigation. This is based on the responses they are seeing in your exercise stats. A lot of times Fourth Frontier does these types of sales so it is worth checking their website from time to time.

Update 15 May 2022: Since this review was published Fourth Frontier have introduced functionality which allows users to connect their Garmin account directly with the Frontier X smartphone app. This is useful as it allows for syncing of GPS maps of your exercise from your Garmin account to the Frontier app and web dashboard.

In other news, Frontier X2 has now been introduced. The second generation product looks the same as the first generation and much of the functionality is unchanged.

The main upgrades are as follows:

  • Three times faster wireless data sync of data from Frontier X to the smartphone app
  • faster updates for heart rate on connected devices
  • a more detailed ECG/Electrical Rhythm view in the mobile app (this is actually also available for the 1st generation product).

You can read more about Frontier X2 on this link.

*We are a review site that receives a small commission from sales of certain items, but the price is the same for you. Purchasing items by clicking on links in this article allows us to run this website. We are independently owned and all opinions expressed here are our own. See our affiliate disclosure page for more details.

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Marko Maslakovic

Marko founded Gadgets & Wearables in 2014, having worked for more than 15 years in the City of London’s financial district. Since then, he has led the company’s charge to become a leading information source on health and fitness gadgets and wearables.

4 thoughts on “Frontier X review: train with confidence you are not over-straining your heart

  • Fourth frontier x and Fourth Frontier x2 both same?
    Please let me know.

  • Excellent review.

    • Thanks – its a good product. Pricey – but the additional stats are useful. At the moment they are working on Afib detection – but that’s still in testing stage.


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