If you follow my training journey, you know I’m meticulous about tracking data. Whether I'm out for an early morning run or spinning on the trainer, having an accurate heart rate reading is non-negotiable. I recently dropped by the Decathlon Sri Damansara branch and picked up the Decathlon HRM Armband (Brassard)for RM149.
One minor caveat: The 26mm strap isn't sold as a standalone spare part by Decathlon Malaysia just yet. If you wear it out over months of sweaty mileage, you will have to scour third-party online platforms to find a generic replacement.
- Powering On: A single quick press turns it on, flashing a blue light as it begins searching for a signal. It features dual-protocol ANT+ and Bluetooth Smart connectivity, making it universally friendly.
- Pairing: It paired instantly as an external sensor with my Garmin Forerunner 965 and my Edge 1040 Solar. If you run older ecosystems from Coros or Suunto that rely heavily on ANT+, it should connect without a hitch, though it’s always wise to double-check your device's specific specs. Once paired, the blue indicator light switches off so it isn't distracting you during night runs.
- Powering Off: Hold the button down for 3 seconds. It will blink to indicate battery status before shutting down—a green flash means you are sitting safely above 20% battery life.
Real Life Test
Wrist HR vs Optical Armband HR: Does Sensor Position Really Matter?
Heart-rate data has become almost invisible in endurance training. Start the watch, start running, and a few seconds later there’s a number telling you how hard you’re working.
But how much should we actually trust it?
I recently compared wrist-based optical heart rate against an optical HR armband during training. Both use essentially the same underlying technology, photoplethysmography or PPG, which detects changes in blood volume beneath the skin. The big difference is where the measurement is taken.
And that seemingly small change in location can make a surprisingly noticeable difference.
Wrist HR vs Arm HR: Same Technology, Different Location
A modern sports watch shines light into the skin at the wrist and uses the reflected signal to estimate each heartbeat.
An optical armband works on the same principle, but places the sensor higher up the arm or forearm.
That potentially gives the armband an advantage.
The wrist is constantly moving during running. Watch movement against the skin and changes in contact between the optical sensor and wrist can interfere with PPG measurements.
Research has nevertheless shown that wrist optical HR can perform quite well during relatively steady walking and running. One study involving 50 participants found mean absolute percentage errors of roughly 3.3% to 6.2% across six optical HR devices compared with a Polar chest strap. [pmc.ncbi.nlm.nih.gov]
The problem becomes more apparent as exercise and movement become more demanding.
A 2025 study comparing a wrist-worn Fitbit Charge 5 against the Polar H10 found that measurement error could increase at higher exercise intensities, with the magnitude of error also differing across skin tones.
Rather than simply comparing the final average HR, I would pay particular attention to the HR trace over time.
Two sensors could both produce, say, an average of 148 bpm, while behaving very differently during the workout.
If the actual HR rises:
140 → 150 → 160 → 170 bpm
but one device responds:
140 → 143 → 152 → 164 bpm
the final averages might look reasonably close, yet one sensor isn't necessarily giving you the same information when you need it.
That's particularly important for intervals.
Why I Prefer the Armband for Training
Interestingly, newer research directly investigating anatomical placement supports the idea that where an optical sensor sits matters.
A study comparing the Polar Verity Sense on the forearm, a Garmin Forerunner at the wrist and multiple WHOOP 4.0 sensors at different arm positions against a Polar H10 found accuracy was excellent at rest but generally declined as movement intensity increased. [mdpi.com]
That's why an optical armband represents an interesting middle ground for endurance athletes.
| Wrist optical | Optical armband | |
|---|---|---|
| Convenience | ★★★★★ | ★★★★☆ |
| 24/7 monitoring | ★★★★★ | ★★☆☆☆ |
| Steady running | Good | Very good |
| Rapid HR changes | More challenging | Generally better positioned |
| Cycling | Can be affected by wrist position | More isolated from wrist movement |
| Comfort | Nothing extra to wear | More comfortable than a chest strap for some |
| Training HR | Good for many sessions | My preference if HR matters |
But What About a Chest Strap?
If outright HR accuracy is the objective, I'd still consider an ECG-based chest strap such as the Polar H10 the benchmark rather than either optical solution.
That's an important distinction.
This isn't really:
Armband = perfectly accurate
It's more:
Wrist → optical armband → ECG chest strap
as you move from maximum convenience towards a more dedicated HR measurement solution.
For long easy runs and everyday training, wrist HR may be completely adequate.
For a five-hour ride, I'd happily use an optical armband if comfort mattered.
The biggest lesson from my comparison isn't that wrist-based HR is bad.
It isn't.
Wrist HR has become good enough that for a huge percentage of my training, I could simply wear the watch and forget about it. Previous validation research has found surprisingly good performance from several wrist/arm optical devices during continuous walking and running. [pmc.ncbi.nlm.nih.gov]
But "good enough" and "the measurement I want to base my training on" aren't quite the same thing.
For me, an optical armband occupies a sweet spot.
Watch only: everyday training and convenience.
Optical armband: when I care about HR data but don't want a chest strap.
Chest strap: intervals, threshold testing and sessions where HR accuracy really matters.
And perhaps that's the better way to look at heart-rate sensors.
Don't ask which one is best?
Ask:
How accurate does this particular workout need to be?
That determines what I put on before pressing Start.
- Price: RM149.00
- Weight: 21g
- Connectivity: Bluetooth & ANT+
- Battery Life: ~30 hours (1-hour fast charge)
- Strap Width: 26mm Velcro
- Warranty: 2 Years
