polar a370 display screens quotation

You can choose on which hand you want to wear your A370 either in the Polar Flow web service or the Polar Flow mobile app. The setting changes the orientation of the A370 display accordingly.

The current time and its format are transferred to your A370 from your computer system clock when you sync with the Polar Flow web service. To change the time, you"ll first need to change the time zone on your computer and then sync your A370.

If you change the time or time zone on your mobile device and sync the Polar Flow app with the Polar Flow web service and your A370, the time also changes on your A370. Your mobile device needs to have Internet connection available in order to change the time.

This study aimed to examine the validity of HR data from 2 wrist-worn HR trackers, the Tempo HR, a low-cost device used for a national PA promotion campaign in Singapore, and the Polar A370, a consumer-based fitness and activity tracking device, in laboratory and free-living settings. Both these trackers have not been assessed previously.

During the first visit, we collected sociodemographic information and measured height and weight with a SECA stadiometer (SECA GmbH). Following this, participants were fitted with 3 HR monitoring devices. We used the chest-strapped Polar H10 HR monitor (Polar Electro Oy) as our criterion device. Concurrent validity of similar Polar devices against echocardiogram (ECG) is well established [

After completing the cycling protocol, participants were introduced to the procedures of the free-living phase. In addition to the devices used in the laboratory phase, we provided participants with an ActiGraph wGT3X+BT accelerometer (ActiGraph) to collect HR data from the Polar H10 chest strap via Bluetooth. The small tamper-proof device was attached with a belt to the right side of the hip. We also provided an instruction sheet detailing adequate wear.

The sampling frequencies of the Tempo HR, Polar A370, and Polar H10 chest strap were 0.1 Hz, 1 Hz, and 1 Hz, respectively. As such, HR data were collected every second by the Polar devices and every 10 seconds by the Tempo HR (a sample of the raw data is provided in

We calculated the intraclass correlation coefficients (ICCs) using mixed effects models to assess the absolute agreement between the criterion (Polar H10) and the other trackers (Tempo HR and Polar A370) in the laboratory phase and free-living phase. The strength of the ICC was interpreted as weak (<0.50), moderate (≥0.50 to 0.74), strong (≥0.75 to 0.89), and very strong (≥0.90) [

We then calculated mean absolute errors (MAEs) and mean absolute percentage errors (MAPE; absolute error/criterion×100) between the criterion (Polar H10) and, both, the Tempo HR and the Polar A370 trackers, to gauge overall measurement error. As highlighted in a recent study, there is no clear cutoff for what level of error would indicate adequate validity between measures [

Moreover, we ranked the 10-second HR time points derived from the Polar H10 and divided them into deciles. As such, decile 1 contained the lowest 10% of all HR and decile 10 contained the highest 10% of all HR. We then time matched these HR deciles with HR data from the Tempo HR and Polar A370. We constructed the box plots to compare the HR data from the Tempo HR and the Polar A370 with the Polar H10 measures across the deciles.

Finally, we constructed 2×2 tables to estimate the sensitivity and specificity of the 2 trackers for identifying the different HR zones based on the Polar H10 (<64% HRmax and ≥64% HRmax). The cutoff of 64% HRmax was chosen because it is the updated cutoff [max cutoff [

In the laboratory phase, the HR data from the Tempo HR showed a moderate ICC (0.51; 95% CI 0.38 to 0.60) with the data from Polar H10. With a MAE of 15.1 bpm (95% CI 14.6 to 15.5 bpm) and an MAPE of 13.0%, the measurement error was somewhat large. Polar A370 data also had a moderate but stronger ICC with the Polar H10 (0.73; 95% CI 0.66 to 0.78). Measurement errors were small with a MAE of 7.3 bpm (95% CI 7.0 to 7.7 bpm) and an MAPE of 6.4%. On average, both the devices underestimated HR: Tempo HR by 9.7 bpm (95% CI −10.2 to −9.2 bpm) and Polar A370 by 5.7 bpm (95% CI −6.1 to −5.3 bpm).

The ICC between the Polar H10 and the Tempo HR data was moderate in the free-living phase (0.71; 95% CI 0.70 to 0.71). Errors were smaller compared with the laboratory phase with a MAE of 8.7 bpm (95% CI 8.7 to 8.8 bpm) and an MAPE of 10.2%. For the Polar A370, the ICC between the Polar H10 and the Polar A370 tracker data was strong (0.83; 95% CI 0.79 to 0.87). Errors were similar compared with the ones in the laboratory phase with a MAE of 5.9 bpm (95% CI 5.8 to 5.9 bpm) and an MAPE of 7.1%. In contrast to the results from the laboratory phase, both the devices overestimated HR slightly (Tempo HR 0.4 bpm; 95% CI 0.3 to 0.5 bpm and Polar A370 3.4 bpm; 95% CI 3.3 to 3.4 bpm).

When analyzing how many MVPA time points were identified by the Tempo HR and the Polar A370, we set the MVPA cutoff at 64% HRmax. In the laboratory phase, of the total aggregate time points in the MVPA HR zone that were detected by the Polar H10, 62.13% (1872/3013) were also identified by the Tempo HR, whereas the Polar A370 identified 81.09% (2273/2803). The remaining time was spent below the MVPA HR zone, of which 91.52% (4267/4662) and 97.52% (4637/4755) were also registered by the Tempo HR and the Polar A370, respectively. Overall, the Tempo HR identified 79.99% (6139/7675) and the Polar A370 91.42% (6910/7558) of data points accurately.

In the free-living phase, we found that the Tempo HR identified 54.27% (5717/10,535) and the Polar A370 identified 83.55% (9323/11,158) of the MVPA time points that the Polar H10 registered. The Tempo HR picked up 97.22% (186,402/191,741) and the Polar A370 picked up 96.72% (183,625/189,861) of time points below the MVPA HR zone. Overall accuracy was above 90% for both the trackers (Tempo HR: 94.98%, 192,119/202,276; Polar A370: 95.98%, 192,948/201,019). An overview of the results is provided in

Number of 10-second matched time points spent in heart rate zones as detected by the Polar A370 and the Tempo HR in the laboratory phase and free-living phase.According to Polar H10≥64% HRmaxa, n (%)<64% HRmax, n (%)Laboratory phase

From the present 2-phased tracker validation study involving 55 participants with varying characteristics, a few key findings can be highlighted. First, HR data from the low-cost Tempo HR tracker showed moderate agreement with the data from the chest-strapped Polar H10 in both the laboratory phase and free-living phase. Although the measurement errors of the Tempo HR were above the 10% validity cutoff [

To establish the stability of the study results, we conducted sensitivity analyses. For this, we removed outliers and compared Polar H10 with the 2 other trackers using the remaining matched data points available. Outliers were defined as follows: a Pearson correlation coefficient of less than 0.3 between the Polar H10 and the test trackers in the laboratory setting. In secondary analyses, we only used data that were available from all 3 devices. Conducting these analyses did not change the results markedly (data not shown). As such, the reported results are not influenced by extreme cases or outliers.

When contextualizing our laboratory findings with those reported in the literature, the Polar A370 and the Tempo HR appear to have comparable or better accuracy with the market leader Fitbit, which has been studied extensively [

Comparing our results from the free-living phase with the results reported in other studies is problematic as, to our knowledge, there are only 2 studies that had a free-living element [max was used, whereas Gorny et al used the older 50% HRmax cutoff. One study by Nelson and Allen also provides some information on the accuracy of a Fitbit device in a free-living setting (Fitbit Charge 2). Over a 24-hour period, agreement measured by the concordance correlation coefficient was 0.91; this is close to what we found for the Polar A370 (although we used the ICC that provides similar estimates). MAE (4.9 bpm) and MAPEs (6.0%) for the Fitbit Charge 2 were also similar to that of the Polar A370 in our study (5.9 bpm, 7.1%). From these results, it appears that the Polar A370 is similarly accurate as the Fitbit Charge in free-living settings, whereas the Tempo HR appears to be less accurate.

Monitor your heart rate and track your sleeping patterns with the Polar A370 - Activity Tracker with Heart Rate Monitor. The sleek fitness tracker monitors your daily steps, distance and calories burned, and sends smart notifications to your Polar A370. It also uses your phone"s GPS to track speed and distance during your outdoor workouts. Train smarter with Polar’s trusted training features, with heart rate zones and the Polar Running Programme.

After just shy of five years since Polar’s last multisport product was announced – the replacement for it is finally here: The Vantage series. This series actually breaks the product line into two models, the Vantage V being the higher end touchscreen edition, and the Vantage M being the mid-range non-touchscreen product. Feature wise, they are nearly very similar, both supporting full triathlon modes.

That’s priced at $279USD/EUR. That’s an awesome deal, though it’s also on-par price-wise with the Suunto Spartan Trainer Wrist HR.  In talking with Polar – they were eyeing that watch as their main competitor in this space for the Vantage M.

Meanwhile, as the Vantage M doesn’t have the swanky etching pattern, it does make up for it by having swappable straps. They use standard watch quick release straps. That’s a feature the Vantage V lacks.  Speaking of which, Polar is selling a few straps of their own, and I think the grey one actually looks pretty nice.  The orange will be appropriate for Strava employees.

The muscle load will come primarily from running workouts on the Vantage V with running power, as well as cycling workouts with a cycling power meter. Whereas the perceived effort is asked of you every time you open up the Polar Flow smartphone app and look at one of your workouts:

In many ways, the training load is very similar to what we see with FirstBeat, and even uses some of the same terminology (which in turn is also based on TRIMP).  You can see some of how this flows from one of the pages of a presentation I got from Polar.  Note that the user interface elements on these screens (and really anywhere you see photos in my post) aren’t necessarily final.

In discussing the features with them it takes upwards of a month to get really solid data out of it, and I’m just over a week now – so things are still a bit jello-like in terms of the status it gives me. But I can see it starting to turn a bit of a corner and giving me more useful feedback.  Here’s a shot from Polar on what this should look like longer term:

The next piece of that puzzle is the new Recovery Pro metrics (only on Vantage V). This is driven by data from the Polar H10 HR strap. So if you don’t have that chest strap, you won’t get these metrics. They don’t believe that the optical HR sensor gives them enough accuracy of HRV data to get these details correct. I don’t necessarily disagree with them, but I also don’t think it’s black and white either. I think there’s some middle-ground like what Suunto and Garmin have implemented.

Of course, Polar has done all their own legwork here for both training load and recovery, as opposed to licensing that from FirstBeat like Garmin, Suunto, and probably a dozen others have done.  In some ways, I wonder if that was the right decision. Which isn’t a slight on Polar’s crew – not at all, nor is a direct praise of FirstBeat. Rather, it’s purely a business thought. Polar’s spent a lot of time on something that best I can tell is no better than what FirstBeat offered. And as I’ve noted in the past, many of the people working in this particular space tend to move around between these companies (helped by the fact that they’re all located in Finland).  But I just look at the totality of new features on the Vantage series and wonder if the ROI was there for this, compared to just licensing it.

Next, there’s the settings menu, which they’ve re-aligned a bit of how things look in there. It’s a nice change, a bit cleaner. And for those familiar with the Polar interface you’ll recognize most of the groupings.

And now’s a good time to talk about that beast of an optical HR sensor. I’d love to have sat in on the conversations on the design of this one. It’s got 9, yes 9 LED’s on it. It’s got four sets of dual red/green LED’s, followed by an extra green. And technically, I just lied to you. There’s also an orange LED in there too (absolute center pairing) – making that 10 LED’s. But the orange one isn’t used at this point and Polar isn’t seeing the benefit to enabling it based on their testing to date.

One interesting tidbit that Polar will be doing behind the scenes is retroactively correcting the optical HR readings, within 60-second blocks. So while you’re working out you might see a given incorrect reading (such as 205bpm), but then 60 seconds later the watch will actually correct that in the file in the watch after it does some post-processing.

Polar is looking at patterns more broadly than just typical instant HR validation to correct for errors, and is instead retroactively looking at bits where it got things wrong and fixing them before you ever even upload the file. Of course, it’s a bit hard for me to demonstrate this at this point, but it was pretty interesting to hear that Polar is doing it.

Polar was pretty clear that they wanted to have the most accurate optical HR sensor. And while I don’t have enough data yet to confirm that, early results seem positive. And if nothing else, they could use all those LED lights to land planes in the fog at the local airport.

Ok, onto running we go. Simply because by choosing running I can show you running power. Once we’ve started our run the touchscreen gets disabled and changing pages occurs via button presses – just like most watches.  You can customize these pages on Polar Flow like past Polar watches.

The running power is displayed on what appears to be about a 10-second smoothed average. I based that on how long it took when I stopped running for the power to come down. At this point I think there’s actually a bit too much smoothing in it, but that’s minor stuff they can tweak.  In any event, the running power is based on GPS pace, and not footpod or wrist-detection pace. This is notable because it does NOT work indoors (treadmill), nor should it work in a tunnel Polar tells me (I haven’t found a tunnel long enough to meaningfully test it yet).  Assuming you’re outside though, this data will be written to your files just like a cycling power meter. And 3rd party apps can easily handle it as well.

The next question is whether or not running power is ‘accurate’. Well, first off, if anyone says that it’s accurate or inaccurate, just close that browser tab. Seriously, there’s no definition of that agreed upon by anyone out there with any meaningful scientific credentials. Instead, I’d argue that running power is more in the ‘is it plausible’ range, with a side of ‘is it at least consistent’.  Even Polar noted in my discussions with them that there are many interpretations of how to measure running power and at which point it should be measured.

But certainly you’ll want to know how it compares on the same run to Stryd or Garmin Running Power? No problem, I’ve got you covered down below in the accuracy section on that bit. Short version: It’s half-way in between them. Again, no idea whos right or wrong. But I did encourage Polar to be as open as Stryd, Garmin, and RunScribe have been in terms of publishing papers and studies that support their algorithm and thinking.

Like others, Polar has done a bunch of work on validation here. They too went to a force-plate treadmill to validate their power metrics, and the results they shared in a presentation seem promising. They also went out and did some pretty technical measuring of hills and did all the science math backwards to validate the numbers after test runners ran them. But again, so did Stryd – yet these two companies don’t match on the same run.

Now, don’t mistake me for thinking I’m down on Polar. Cause really, I’m definitely not. Instead, I’m just ‘less optimistic’ about running power in general. Mostly because we can’t seem to get any two companies to agree.  As such, I think it’s tough for consumers (or myself) to know what to make of it. Or whether to trust it when training. Similarly, as much as we as humans want our cycling and running power numbers to equate, there’s no science that says they should. Just like our heart rate numbers for cycling and running certainly don’t match for the same perceived effort.

Moving along to other newness, we’ve got Polar leveraging a new GPS sensor/chipset in their Vantage series. They’ve switched from SiRF to Sony, just like Suunto did in joining forces with Sony. At present Polar is leveraging GLONASS, but not yet Galileo. That’s a limitation by Sony, which doesn’t yet support it. Polar says there’s a chance they’ll be able to update it down the road via firmware update, but that’ll really just depend on Sony doing so.

With this new GPS chipset, Polar is going to be able to get a whopping 40 hours of GPS and optical HR on recording time, all at 1-second intervals. That easily surpasses the 1-second rates of Garmin and Suunto.  But it also falls short of Suunto and Garmin’s less-frequent recording rates aimed at really long ultrarunners. Polar doesn’t have any secondary less-frequent update modes on the Vantage series like it had on the V800.

Finally, as I noted up in the earlier section – there is no routing or navigation on the Vantage series at this point. They do plan to add in a basic “back to start navigation” by the end of March 2019, but there’s no plans for downloadable route navigation like seen on past Polar products. That might make this a tough sell at $499 for some folks, given many cheaper products have that as a baseline.  And once in the Vantage V’s price point, it’s honestly unheard of to not have breadcrumb style navigation and routing. Still, Polar did note in my meeting with them that they’re focused on paying attention to feedback and will certainly take things into account going forward.

And just to be a bit clear on why these features are missing: The Vantage series is a complete code re-write for Polar. Thus unlike new watches of the past where they were essentially just porting code chunks over to new hardware, Polar re-wrote everything here and simply had to make hard choices on what to keep or not. In some ways this reminds me of what Suunto did moving from the Ambit series to the Spartan series.

Now, before we dive into things I do want to stress this is early data. The product is very much still in beta, and isn’t expected to start shipping until later in October. So we’re talking 6-7 weeks away here. That means things will likely get better (though, in rare cases I’ve also seen some products get worse too).  Still, Polar came to the Netherlands to meet with me and hand over watches for me to do my thing with. Thus, good or bad I’m going to share those early results.  Since then I’ve done 1-3 workouts per day with the watch, plus I’ve been wearing it 24×7.

As you can see, things are very close to each other.  And if you had looked past the odd noise of the TICKR-X in the earlier screenshot, you’d have noticed that all four basically agreed.  These were 2-minutes of running at 6:30/mile pace, followed by 60 seconds of 7:30/mile pace. Repeated. Solid stuff.  The blocky bits is just cause we’re super zoomed in, so one 1BPM is causing a bit more of a blocky look at 1-second intervals.

(Note above that the vast majority of those are Polar errors, but the Fenix isn’t without an error or two of its own, which I highlighted with a non-arrow line.)

Now again, as noted, it’s beta. And Polar confirmed they’re working on it (they’ve seen these tracks of mine). So certainly we’ll give them time to sort things out. But I’d also keep this tweet of mine in mind too.  This is all somewhat ironic because during my meetings with them I asked how they were finding the Sony GPS chipset, given Suunto had some teething pains with it (and still does to some degree as you can see above).  They were pretty confident at the time that they were in a good spot, even noting that Suunto probably paved the way for them a bit on early Sony aspects that would ultimately benefit Polar as well.  Unfortunately, that doesn’t yet seem to be the case.

Oh, and finally, running power. As noted above – I’m not about to declare any winner in this battle. I’m just going to plop the data out there and let folks decide what they want to decide.  Here’s one run of mine comparing Polar Running Power (teal) vs Garmin Running Power (purple):

I’ve added the Polar Vantage V & M into the product comparison tool, which means you can compare it against just about anything you want.  For the purposes of this chart I’ve compared the Polar Vantage V with the Suunto 9 and the Garmin Fenix 5 Plus.  Of course, you could remove the Plus part and go with the base Fenix 5 and that’d reduce the price a fair bit (and remove music/contactless payments/maps).  But you can do all that within the product comparison tool here, comparing it against all other GPS watches I’ve ran with to your heart’s content.

From a purely aesthetic and hardware standpoint, the Vantage series is a huge improvement in my opinion. While the older V800 did its job, I’m not sure there were a ton of people that called that baby beautiful. However, I really like the design of the Vantage V especially. The nuance in the etching of the band and the underside of the bezel is really well executed. Same goes for the button etching.  And of course, dem optical HR sensors! It’s clear Polar has spent a good chunk of the time between iterations on the industrial design elements, and it shows.

The challenge though I see for Polar at this point is the software side. In most cases you want a new product to generally carry with it all the features of the previous unit and then add new cool stuff. Polar checked off the ‘cool new stuff’ box, but did so at the expense of some existing features not being in the current watch. While smartphone notifications will come in a future update, more outdoor focused features like track/route navigation aren’t expected to.

Polar was clear in my meeting that they aren’t going to try and compete with Garmin on feature-count. Suunto mirrored those exact words when we met prior to the Suunto 9 launch. Neither has the resources to challenge Garmin on features. Instead, both are aiming to narrow their focus on the performance side of the house. With Polar that focuses heavily on heart rate driven training load and recovery metrics, while also expanding to their own running power solution. Whereas with Suunto that expands more towards ultra runners and their crazy long battery life options.  Both companies have shifted to Sony GPS chipsets, which may work out long term – but short term seems to be challenging for both, based on my testing.

Still I’m looking forward to seeing how the Polar matures over the next 6 or so weeks as they near shipping release. The current plan calls for them to start shipping in late October.  I’ll drop my in-depth review on or slightly after they start shipping.

If you"re shopping for the Polar Vantage M or any other accessory items, please consider using the affiliate links below! As an Amazon Associate I earn from qualifying purchases. It doesn’t cost you anything extra, but your purchases help support this website a lot. Even more, if you use Backcountry.com or Competitive Cyclist with coupon code DCRAINMAKER, first time users save 15% on applicable products!

This is a great strap, especially if you"re going to the gym. It"s dual ANT+/Bluetooth Smart, but it also supports the 5kHz analog heart rate transmission for older gym equipment. Note that it only accepts a single Bluetooth connection, versus dual-connections for the Polar H10.

I"d argue the Polar OH1 Plus is the best optical HR sensor out there. So while it might seem odd to get this when your watch also has a optical HR sensor, this one is just better most of the time. Plus, it also has workout recording storage. Dual ANT+/Bluetooth.

The Polar Verity Sense is the newer variant of the Polar OH1 Plus. And while it might seem odd to get this when your watch also has a optical HR sensor, this one is just better most of the time. Plus, it also has workout recording storage. Dual ANT+/Bluetooth.

If you"re shopping for the Polar Vantage M or any other accessory items, please consider using the affiliate links below! As an Amazon Associate I earn from qualifying purchases. It doesn’t cost you anything extra, but your purchases help support this website a lot. Even more, if you use Backcountry.com or Competitive Cyclist with coupon code DCRAINMAKER, first time users save 15% on applicable products!

This is a great strap, especially if you"re going to the gym. It"s dual ANT+/Bluetooth Smart, but it also supports the 5kHz analog heart rate transmission for older gym equipment. Note that it only accepts a single Bluetooth connection, versus dual-connections for the Polar H10.

I"d argue the Polar OH1 Plus is the best optical HR sensor out there. So while it might seem odd to get this when your watch also has a optical HR sensor, this one is just better most of the time. Plus, it also has workout recording storage. Dual ANT+/Bluetooth.

The Polar Verity Sense is the newer variant of the Polar OH1 Plus. And while it might seem odd to get this when your watch also has a optical HR sensor, this one is just better most of the time. Plus, it also has workout recording storage. Dual ANT+/Bluetooth.

The validity of consumer-targeted wrist-worn sleep measurement systems has been little studied in children and adolescents. We examined the validity of a new fitness tracker (PFT) manufactured by Polar Electro Oy and the previously validated Actiwatch 2 (AW2) from Philips Respironics against polysomnography (PSG) in children and adolescents.

Current Knowledge/Study Rationale: The validity of consumer-targeted accelerometers in measuring sleep is little studied. Most validation studies focus only on devices designed for research use, though sleep-tracking devices are widely used among consumers. This study compared two wrist-worn devices (Polar Electro Oy and Philips Respironics Actiwatch 2) against polysomnography in children and adolescents.

Study Impact: Both wrist-worn devices had high sensitivity, but specificity was generally higher for the Polar fitness tracker than for the Actiwatch 2. The Polar fitness tracker measures sleep at a level generally accepted in clinical and research contexts.

In this study, we set out to assess the validity of a new, commercially available Polar fitness tracker (PFT; Polar Electro Oy, Kempele, Finland) and the previously validated Actiwatch 2 (AW2; Philips Respironics, Murrysville, Pennsylvania, United States) accelerometer against PSG in 11-year-old children and 18-year-old adolescents over 1 night slept at home. In contrast to the accelerometer devices usually used for research purposes, the PFT functions without registering the lights off and lights on times (eg, by pressing an event marker or by using a paper-and-pencil sleep diary). If working correctly, the automatic bedtime detection increases the feasibility of the measurement, as self-reported bedtimes often are not reliable. Manually inserting the analysis windows and selecting correct event markers (often resulting from several markers for one night) also takes considerable time and effort.

We used a prototype PFT that corresponds to the commercially available model A370 fitness tracker, with an embedded micro-electromechanical systems (MEMS) 3D sensor (LIS3DH, STMicroelectronics, Geneva, Switzerland), and a sampling rate of 50 Hz. Data were uploaded to a prototype version of a web service that generated sleep-wake detection in 30-second epochs. The calculation of the sleep variables is grounded on Polar"s proprietary algorithm and is uniform with the “sleep plus” feature that is available in the model A370 fitness tracker and model M430 GPS running watch (Polar Electro Oy, Kempele, Finland). The epoch-specific sleep-wake classification was exported from the service.

Bland-Altman plots of the correspondence of the actual sleep time between the devices in the younger (upper panels) and older (bottom panels) age groups. (A1,A2) PSG and PFT, (B1,B2) PSG and AW2, (C1,C2) AW2 and PFT. AW2 = Actiwatch 2, PFT = Polar fitness tracker, PSG = polysomnography.

We studied a new PFT, equivalent to their commercially available model A370 fitness tracker, that operates through their proprietary web service, and the previously validated AW2, a device mainly targeted to clinicians and researchers. We studied the validity against PSG in two age groups, one prepubertal and the other postpubertal. In this study, we found an adequate and comparable measurement validity for both accelerometers over 1 night of measurement. At some points the PFT outperformed the AW2. Both devices were adequately accurate in measuring sleep onset. When measuring sleep offset, the AW2 had a statistically significant difference from PSG—underestimating sleep offset in the younger group, and overestimating sleep offset in the older group. Both devices underestimated actual sleep time and overestimated WASO in both age groups.

This study was conducted with great care to ensure a reliable comparison of two different accelerometers and PSG. However, some limitations are present within this protocol. First, the small sample size including only healthy participants restricts the external validity of our results. Thus, sleep-wake-measurements from children or adolescents with health issues or sleep disorders might not be estimated as accurately as in this sample. Second, the consumer products do not usually give epoch-specific data to the user, so a collaboration with the manufacturer is a necessity for potential replication studies. In these cases, it is crucial to design the data flow such that the manufacturer does not have access to the PSG data at any stages to maintain impartiality, as was done in our study. It should be also emphasized that we used a prototype of the commercially available model A370 fitness tracker, but it was similar in size and appearance to the final product. Third, our comparison covered only 1 night without any adjustment period; hence, it is possible that we did not capture the full scope of typical sleep behavior. Fourth, we did not balance the position of the accelerometers in the same wrists, but all measurements were conducted with PFT being on top of the pisiform bone, and AW2 1–2 cm above (closer to the torso). This may have been biased either way for estimations. Finally, the sample size was rather small for detecting statistical significance of any potential sex differences.

Work for this study was performed at the Department of Psychology and Logopedics, University of Helsinki. All authors have seen and approved the final version of the manuscript. The research work (conducting the study, analyzing the data, writing the manuscript) was not covered by any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Polar Electro sponsored the immediate expenses from the research nurse, research assistant, and the participant incentives. The sponsor provided the Polar prototype devices to the study, agreed on the study design by the authors, and provided the data summary (epoch-by-epoch data are not openly available through the consumer product) and technical details of the device. Polar Electro had no involvement in the analysis and interpretation of data; nor in the writing of the report; nor in the decision to submit the article for publication. Acknowledging the role of the funding source as explained, the authors take complete responsibility for the integrity of the data and the accuracy of the data analysis and report no individual conflicts of interest.

Polar"s new A370 fitness-tracking wristband is a course correction from its predecessor, the A360, which was lacking in a few key areas. The A370 improves upon the last-gen model, with continuous heart-rate monitoring, GPS (sort of), an easier-to-fasten band clasp and a new sleep-tracking tool called Polar Sleep Plus.

But the $179 A370 is also a direct shot at Fitbit, the category leader, with a handful of marquee features yanked straight from last year"s best-selling Fitbit Charge 2. Can Polar out-Fitbit Fitbit? Spoiler alert: no.

The A370 looks almost exactly the same as the A360. Both have beautiful, bright, full-color TFT capacitive touch screens that show the time when you move your wrist. Fitbit"s Charge 2 also has a touch display, but I prefer the A370"s because it"s much longer and can show more information at a glance.

When you swipe down from the main clock view, you"ll see settings, your heart rate and an overview of your daily activity. You can also start a training session from that menu. A bigger display makes it easier to see data at a glance while you"re running outside, which is a bonus.

To sync the tracker with the Polar Flow app, press and hold the side button on the A370. (It"s bizarre that this function has a dedicated hardware button.) The same button will pause or end a workout. The A370 supports phone notifications from any app, which is far better than what the Charge 2 offers: limited text, call and calendar alerts. Like the Charge 2, the A370 also enables alarms and sends you messages encouraging you to move. All of these alerts are accompanied by a strong vibration, which will definitely wake you from a dead sleep. Trust me.

But the A370 still looks very much like a run-of-the-mill fitness band. Its six interchangeable straps are available only in a sporty elastomer material, which you won"t want to wear with a dressy outfit or to a fancy event. Polar offers two band lengths, small and medium/large, but if you have a small wrist, the A370 will look massive. There"s no getting around it. I prefer the size of Fitbit"s Alta HR over both the Charge 2 and the A370, which both look ridiculous on me. But the A370"s larger display almost makes up for its all-around huge size.

I do like the in-app sleep-continuity rating, which tells me how many times I woke during the night, and the ability to give my own feedback on each night"s sleep. Polar"s nightly report also includes your lowest heart rate during sleep, which Fitbit"s doesn"t. While that data point is probably more useful to people with sleep disorders or heart problems, I still found it fascinating.

Optical heart rate sensors have improved by leaps and bounds over the last few years. I took the A370 on several 3-mile runs over the course of a week and a half, and it consistently and accurately tracked my heart rate. I strapped a Polar H10 heart rate monitor to my chest for comparison and got almost exactly the same results.

Frankly, the connected GPS was annoying. First you have to change your smartphone settings to allow Polar Flow to constantly track your location, which is a setting I hate to turn on for any app. Without doing that, you won"t get maps of your routes. Even after I changed my settings, the A370 kept losing the GPS signal on my morning runs and vibrating my wrist every single time to alert me. That may have been the fault of my iPhone 7 Plus and Brooklyn"s tree-lined streets and parks, but it was still irritating. The Polar Flow app still managed to accurately map my route and graph my pace per mile, but those constant vibrations killed me.

The Activity tab gives you an overview of your day with charts and graphs galore, and includes data on workouts and sleep. But then workouts and sleep get their own tabs with deeper insights, because why not? The whole app could use a streamlined redesign. This is where Fitbit shines. Its app is gorgeous; its social features are easy to find and use, and I don"t have to dig around to find the data I want to see.I took the A370 on several 3-mile runs over the course of a week and a half, and it consistently and accurately tracked my heart rate.

Polar has another app, Polar Beat, which syncs with the company"s H10 chest strap and offers voice coaching. That app looks like a million bucks with a very Apple-inspired design, but it offers far fewer features than Polar Flow. If Polar would marry the two, I would love the A370 a whole lot more.

The A370 wins bonus points for using a micro USB cable instead of a proprietary charger, though the port cover feels flimsy, like I might lose it at any moment.

The A370 is a vast improvement over the A360. It offers accurate, continuous heart-rate tracking; connected GPS; deeper sleep insights; and a better band clasp at a lower price than Polar"s previous band.

If you"re a serious athlete, a more fully-featured GPS watch, such as the Garmin Forerunner 35, would be a better investment. If you just want a fitness band that can track your exercise and sleep without too much fuss, the A370 is a good option. But Fitbit"s Charge 2 is less expensive and offers many of the same features, with the bonus of a great app and interchangeable bands that can transition from the gym to the office.Today"s best Polar A370 deals

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