After telling a friend that I got a Garmin Fenix 6X, he said that they were no good for heart rate because the optical heart rate sensor could not capture peaks. This lead me to do some research, so I searched around and found a video – which seemed to support what he was saying:
https://www.youtube.com/watch?v=WvDfl_2zxmA&t=239s
The video showed that, compared to a chest-strap, the Garmin watch tended to not give readings about 165. Now I was a little concerned, so I set out to do a test. First I prepared my new as of September 2020 6X Sapphire that I got fresh from Garmin. Yes, this one has a black screen. I used a silicon band, and made it snug, but not overly tight. The GPS was set to GPS+GLONASS. Then I got my iphone 11 Pro Max, and paired a Polar H7 Bluetooth HR chest strap to it. I set this up with the Wahoo app, since Strava no longer supports direct connections to HR sensors. I headed to a high-school track so that I could also test the GPSs.
First, I walked 3/4 of the track to let the GPSs warm up for four minutes. When I got to the start line, I walked along it a few times, for the goal of being able to later make a segment from this start line. Then I circled around, and ran through the start line. When I got to the same finish line, I went back to walking. I then alternated running and walking for a few laps. In my mind, based on my experience, I got my heart rate past 170bpm.
As for the GPS, the Garmin watch was much better. I also saw this a few days ago when I rode a hilly and densely wooded MTB course with each.
The heart rate data was surprising. Mostly they tracked about the same, though the Garmin seemed delayed a bit. I am not sure what this means, since I started both tracks within 1/2 a second of each other. There is one area where the chest strap showed 213 bpm, while the optical watch never went over 180. Which to believe? Well, I am age 51, and have been using HR chest straps for many hours, including for stationary bike FTP tests. I don’t think I have ever seen a reading over 188 or so, so I tend to believe the 180 more than the 213. In any case, the Garmin watch with 11.75 firmware is capable of showing HRs over 165bpm. Also, I have been swimming with this a lot lately, and the HR appears to work well under water while the watch counts the laps.
In conclusion, I am loving this GPS accuracy, and the entire 6X experience. The battery life is great – between 5 and 16 days for me, depending on if everything like HR and pulse-ox is on or off. Compare that to my Apple Watch Series 5, which needed to be charged daily – and for which I could not wear at night since it was charging. I wanted to sleep-track, and with the Garmin, that is finally practical. The optical HR shows data that I suspect is of reasonable quality, and I am surprised that my long-time owned chest strap is showing questionable data.