I've long suspected that my Fitbit's heart rate was... well, "inaccurate" isn't the right word. I've confirmed with other devices (manual timing, blood pressure cuff with hear rate, etc) that my watch IS accurate, but not always.
Specifically I notice quite a discrepancy when my heart rate increases at the beginning of an exercise. I've posted a screenshot of a great example. This represents me starting an exercise manually on the watch immediately before a go up a very steep hill, then back down and up it again. Focus on the first part of the chart. My HR goes up immediately, but then plummets and stays low for a bit before skyrocketing up to peak.
That simply did NOT happen. At one point I was out of breath and I tried manually clocking my HR and it was fast enough I couldn't keep count. I estimate it was 160, yet my watch showed 85. This repeated the second time I started up the hill. This is a LONG hill that has a sustained grade. It is a tough hike.
I added a green line to the screenshot for how I would say my HR went during that session. Again, both times I started up the hill when my HR spiked in a short amount of time, the watch recorded it as going up briefly, then down (which simply did not happen) before correcting eventually.
Is this a known limitation of ALL Fitbits, or are newer models better at this?
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