For years, Arturo and I have joked that the heart rate monitors built into Garmin watches are random number generators. We would kill ourselves and the HR would read some obnoxiously low reading, like 120bpm. We would start a descent, and the HR would give us an absurdly high number like 144bpm. This occurred across multiple generations of watches and sensors. People with white skin do not seem to have a problem.
I tried switching to the Schosche Rhythm 24 as an external HRM. While that HRM was much more accurate, it was subject to multiple dropouts from the Edge 840. If you read various forums, that dropout is usually blamed on Garmin's firmware. On the other hand, the Edge never experienced any dropouts from my Fenix watches.
I then theorized that the reason the cheap $30 HRM would outperform my $700 watch was positioning. The wrist is a poor position for an optical HRM. Not only does it not get signal from blood vessels easily, but (especially on thin-wristed people) it's subject to vibration and noise. The upper arm position that the Schosche Rhythm 24 demands probably contributes to its improved accuracy. My solution was to look for an elastic strap that would let me wear the Fenix like a Schosche during workouts.
The Abanen Quick Fit 22mm Elastic Band was on sale during a Prime day for around $17. That's half the price of the HRM. The quick fit works as advertised, and the band itself dries quickly even when submerged in water. I adjusted the strap so that it could be used both on the wrist (albeit suboptimally) and on the upper arm. The difference was immediate and visible. Any moderate effort would push the HR reading on the Edge to 120. A tough climb at 200W would slowly drive my HR up to 150, and a sustained push beyond that will get it to 170. Garmin's connect app stopped complaining that I had a high aerobic shortage.
It took me years to figure out the problem, but now that I have, this setup cannot be beat for touring. I have a HRM for rides, plus a hiking GPS and step counter off the bike. And of course, it also means that things like HRV are probably suspect if you're wearing your watch on the wrist as you sleep!!
Needless to say, the Abanen comes highly recommended!
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