The chest strap is still the gold standard for accuracy, but it slips, it chafes, and plenty of runners end up tossing it in the back of a drawer. For several years now, Polar has offered an armband alternative, the OH1+, which reads your heart rate optically on the biceps or forearm instead of the chest. At RunMorph, this sensor keeps coming up whenever we recommend something to runners who can't stand a chest strap. The real question: what is it worth after long-term testing?
© Polar, official photo used for editorial purposes
Polar OH1+: the armband that wants you to forget the chest strap
Polar was one of the first brands to mass-produce a consumer heart rate chest strap back in the 1980s, and the Finnish company is still closely tied to the Polar H10, the absolute benchmark for accuracy. But the chest strap has a built-in flaw: it chafes, it slips under several layers of clothing in winter, and some runners simply can't tolerate it. The OH1+ tackles that problem with a different approach from the more recent Polar Verity Sense: a 5 g optical pod clipped onto an elastic armband, worn on the biceps or forearm rather than the wrist or chest.
On paper, it's a risky bet: the optical sensors built into watches have a bad reputation when the pace changes suddenly. But moving the sensor to the arm, away from a wrist that never stops moving, changes everything. That's exactly why this format has lasted so long at Polar, and why Wahoo (TICKR Fit) and Coros (HR Monitor, already reviewed by RunMorph) offer their own versions.
A 6-LED optical sensor on the arm: what does it really change?
The technology itself is nothing revolutionary: six LEDs track changes in blood volume under the skin, just like any watch's optical sensor. What changes is the location. On the biceps or forearm, the muscle mass is more stable than at the wrist, which cuts down on the motion artifacts behind phantom spikes during intervals. The clip that comes with the sensor also lets you attach it to your swim goggle strap for a reading at the temple. That area stays out of the water most of the time, so you lose the signal less often, an advantage neither a classic chest strap nor a wrist sensor offers.
Simultaneous Bluetooth Smart and ANT+ connectivity lets you broadcast your heart rate to several receivers at once (a watch and the Zwift app, for example), although Bluetooth remains limited to a single active connection, unlike the Polar H10, which accepts two.
RunMorph tip: for running, wear the OH1+ on your forearm, on the inner side. It's the position that gives you the best day-to-day balance of accuracy and comfort, even under long sleeves in winter. For swimming, use the goggle clip rather than the armband: the signal is noticeably more stable there.
The field test: from easy runs to the pool, a sensor that delivers
Several independent French-language reviews ran the OH1+ through months of full training, alongside a reference chest strap. The consensus is clear on easy aerobic running: an average gap of less than 1 bpm compared with a Garmin HRM-Run strap, with the curves almost perfectly overlapping outside the first two minutes of effort. On a hilly course with swings between 135 and 175 bpm, the gap rises slightly but stays under 2 bpm, with only very brief, occasional dropouts.
The consensus breaks down on very short, intense efforts. On intervals above 160 bpm, one independent test reports up to three out of five peaks missed, and on very short 30/30 sessions, several testers note a clear lag both on the way up and during recovery. A different test, run alongside a Garmin HRM-Tri strap and the optical sensor of a Garmin Fenix 6, reaches a similar conclusion: accuracy matches a chest strap on most easy, tempo and threshold sessions, with no notable lag reported for running or cycling.
In the pool, the reviews also agree: the signal stays stable with rare dropouts, whether you use the goggle clip or the biceps armband, and for the first time many swimmers can see their heart rate in real time during pool sessions. Battery life is where the measurements diverge a little: one source reports 11 h 16 min measured against a claimed 12 h, another tops out at around 10 hours. Either way, the gap with the manufacturer's claim is real but manageable with a weekly charge if you train 10 to 15 hours a week.
One thing every independent review we read for this test has in common: the lack of a reliable battery indicator during use and an awkward power button (sometimes you need a fingernail) keep coming back as the product's real ergonomic weak point, more than the accuracy itself.
Polar OH1+ vs Coros HR Monitor: head to head
| Criterion | Polar OH1+ | Coros HR Monitor |
|---|
| Format | Biceps/forearm armband | Biceps armband |
| Weight | 17 g | Comparable, soft armband |
| Battery life | 10 to 12 h | Up to 38 h |
| Internal memory | 200 h | No |
| Connectivity | Bluetooth + ANT+ | Bluetooth only |
| Swim clip | Included | No |
| Ecosystem | Polar Flow, universal | Coros app, ideal with Coros watches |
| Official price | €79.90 | €89 |
The Coros HR Monitor wins by a wide margin on raw battery life, a strong argument for ultra trail runners. But the OH1+ keeps the edge on multisport versatility thanks to its swim clip and 200-hour internal memory, two features its direct competitors lack.
What we liked
- Barely noticeable comfort: 17 g in total, and you quickly forget the chest strap
- Reliable accuracy on 80% of sessions (easy, tempo, threshold)
- Real versatility: running, cycling and swimming with the same sensor
- Universal Bluetooth + ANT+ compatibility with every watch brand
What we liked less
- Measured battery life between 10 and 12 h, far from the 30 to 38 h of direct competitors
- Accuracy drops off on very short, intense intervals
- Only one simultaneous Bluetooth connection, versus two on the Polar H10
- No reliable battery indicator during use
Our field take: who is the Polar OH1+ for?
The OH1+ makes sense for runners who have already tried a chest strap and given up on it because of discomfort, and for triathletes who want a single sensor for all three disciplines. For the easy, tempo and threshold sessions that make up most of a training plan, its accuracy is more than enough. Only when you hit very short, intense intervals does the chest strap regain the upper hand.
Whether you're following a marathon, half marathon or 10K plan on RunMorph, the OH1+ handles your long runs, easy runs and threshold sessions without a hitch. For the short, high-intensity interval blocks in your buildup, keep a chest strap on hand if you want maximum accuracy on every peak.
RunMorph Coach's verdict
The Polar OH1+ delivers on its promise: near-total comfort and accuracy that rivals a chest strap on the vast majority of training sessions. Its multisport versatility, backed by the swim clip and 200-hour internal memory, makes it a smart pick for triathletes and anyone allergic to chest straps. But the 10 to 12 hours of battery life, decent at best next to the 30 and 38 hours of direct competitors Wahoo and Coros, plus Bluetooth limited to a single device, keep the score from climbing higher. 7.8/10: a very good sensor if you value comfort and versatility over extreme battery life.