Sunday Runday
In this weekly column, Android Central Wearables Editor Michael Hicks talks about the world of wearables, apps, and fitness tech related to running and health, in his quest to get faster and more fit.
Heart rate monitor chest straps earn their reputation as the gold standard for workout accuracy. When it works as intended, my Polar H10 ECG delivers precise, quick-adapting results, and I’ve used it for many reviews and accuracy tests against smartwatches to see how good their optical sensors are.Â
Despite all that, I’m ready to move on from chest straps, both professionally and personally.
My thoughts on this coalesced when I performed a Galaxy Watch Ultra accuracy test. Samsung promised a revamped optical sensor that would prevent light artifact issues during anaerobic workouts, so I tested the results against my COROS Heart Rate Monitor, an optical HR armband.Â
Someone reposted the article on r/GalaxyWatch on Reddit, and the responses ranged from calling the test “kinda pointless” because I didn’t use a chest strap to “Trusting Android Central to do a fitness device review? lol.” To paraphrase my childhood hero, Michael Jordan, I took it personally.
Why people trust chest strap heart rates (and don’t trust OHRs)
There’s a widespread assumption that optical heart rate (OHR) straps can’t be trusted, and journalists who use them for testing are wasting people’s time. It’s a reasonable belief but one that needs to be debunked.Â
Any fitness smartwatch or tracker, smart ring, or armband uses LEDs to illuminate your skin and photodiodes to catch the reflected light, visually tracking changes in your pulse. It’s generally reliable but prone to errors if the PPG sensors aren’t perfectly flush; arm movement introduces gaps that let in light and sweat that skew the results.
The Galaxy Watch Ultra and Pixel Watch 3 add more LEDs and new algorithms to try and solve the light artifact issue. Samsung and Google have a bad track record at supporting external heart rate monitors, so I do at least appreciate the effort, even if early tests suggest they have more work to do.
A chest strap bypasses these LED issues. It uses an electrocardiograph (ECG) to read your heart muscle’s electrical rhythm at its source instead of further out, where changes in blood flow might take longer to register.
Since OHRs can struggle with accuracy on darker skin tones — some brands address this issue better than others — many athletes only trust chest straps.
That isn’t to say a chest strap magically gives you perfect results every time. According to Polar, you must moisten the Polar H10’s electrodes with water, gels, or saliva (ew) before sweat kicks in and improves the connection. Chest hair can block the signal, as can static from a synthetic shirt or other electrical sources. And you’ll need a tight enough strap to maintain the connection.
But beyond that, they’re also uncomfortable! I’m happy for people who’ve Stockholm Syndromed themselves into getting used to chest straps’ fit, but the restrictive feeling keeps me out of my running “zone.” I put up with it (until now) because I wanted to give readers accurate testing results.
Why I’m using an OHR arm band for testing accuracy
An OHR armband properly fitted to your biceps avoids a wrist-based sensor’s issues. You have much more surface area for LEDs to read your pulse, it’s more comfortable to secure tightly, and there’s no bending joint to cause accidental separation during exercises like push-ups.
I received the COROS Heart Rate Monitor for a review, and it delivered accurate results. I gifted another COROS band to my partner, who’s had trouble with wrist-based OHR in the past due to skin tone, and she hasn’t experienced the same issues with the arm-based strap so far.
At the time, I read the general consensus on chest straps’ supremacy and bought a Polar H10 to compare the two. Both gave me near-identical results, but I decided to use the H10 for my smartwatch reviews since it was supposedly better.
I don’t know if my H10 is a bit defective, if I’m not wetting the electrodes enough, or maybe the strap isn’t perfectly fitted. But the more I use it, the more I get obvious inaccuracies during the first 10–15 minutes of a workout.
I first noticed this during my Garmin Forerunner 165 track test in March, when the H10 HR briefly dipped from 152 to 138 bpm and stayed flat while my Garmin, Coros, and Fitbit all rose to 166 bpm. But it was just one blip (I thought).
Then, during my Coros vs. Garmin vs. Polar watch accuracy test, I spotted a few moments during a normal run and a track workout where it spiked well above or below all three watches before auto-correcting to its usual perfection, without any adjustments on my end. It made judging the “best” watch OHR harder when my ECG control group was wonky.
After those Redditors decided to come for me, I performed a straightforward COROS HRM vs. Polar H10 test, pairing the COROS to my Garmin Forerunner 965 and starting a workout in the Polar Beat app simultaneously; you can see the results in the charts above (a 10K run) and below (a hard 1-mile track run).
I knew something was off during my first run, even with my phone in my pocket, because Polar Beat kept alternating audio cues for “improving fitness” and “burning fat,” as if I was rapidly changing my heart rate and pace. It was simply losing and recapturing my actual heart rate signal before things settled down, and it remained perfect for 30+ minutes — without any physical adjustment on my part.
During the second test the same day, the H10 immediately claimed that I was at near-max effort before I’d even hit a fast pace, then fluctuated slightly between too high and too low before nailing my heart rate a few minutes in.
To forestall the inevitable comments, I’m not claiming all chest straps are inaccurate. I’m hopeful I can figure out why my H10 has early-run issues. What’s more important is each graph’s second half, where you’ll find Polar and COROS in near-lockstep.
They’re never perfectly aligned. In the first run, whenever I increased my pace or ran up a steep hill, COROS consistently trailed by about 1 bpm before catching up and took slightly longer to register when I eased off. During the second run, Polar registers tiny 1 bpm fluctuations that COROS needs longer to catch.Â
But even chest strap lovers must admit that COROS’ optical HR graph is on point. It catches up quickly and has fewer errors than wrist-based trackers.
Personally, the accuracy gap is so minimal — and the comfort gap so wide — that I’d rather wear my OHR armband; even if it’s not perfect, it’s more than good enough for Garmin or other brands to calculate my general effort and training load. And it’s much easier to forget I’m wearing an armband than a chest strap.
You’re missing the point of these smartwatch accuracy tests
Yes, chest strap heart rate readings are more accurate than an arm- or wrist-based optical sensor. Fitness experts like DC Rainmaker use chest straps as review benchmarks for a reason. If you prioritize accuracy over comfort, buy a chest strap.
But here’s what matters: smartwatches are always going to use optical readings and they’re never going to be as good as chest straps.Â
Why should I exclusively use a chest strap for accuracy tests when that’s a quality standard that a watch can’t reasonably hit? Smartwatch HR accuracy has demonstrably improved across brands in recent years, but if chest straps are the benchmark, then every watch I review is “inaccurate” to some degree.Â
You shouldn’t read smartwatch reviews holding them to the standard of a chest-based ECG unless you’re looking for things to criticize. Instead, a more useful comparison is how its optical HR matches against a COROS HRM or Polar Vertix, both of which negate the usual issues with OHRs like light artifacts. Very few fitness watches come close to that standard, but a few brands are using algorithms to try and close the gap.
It’s not about perfection; it’s about finding watches that are good enough for you to compromise and leave your chest strap at home.
Comfortable and reliable
The COROS HRM targets athletes who want better than a smartwatch’s optical HRM can deliver but can’t force themselves to wear a chest strap. This seamless device simply works as soon as you put it on and goes on standby for up to 80 days once you take it off. It’s comfortable, secure, and reliably accurate.Â
