Vivosmart 4 - bad heart-rate measurement mid-workout

Using a Vivosmart 4.

I am continuously experiencing what is basically the same failure mode. I have attached the graph (from my Garmin Connect account).

As you can see from about the 8 minute mark, lasting for about 2-1/2 minutes, the pulse reading drops to nearly resting heart rate - which is ridiculous, because, at this point in the workout my pulse was climbing quite quickly, and could never have dropped below 110, and certainly not down to 60.

This happens fairly consistently - not necessarily at the some relative time in the workout. I have adjusted the tightness and ensured the inside of the watch is clean before use (wiped down with a clean, damp cloth).

The fact that this happens so consistently - every use - is an annoyance, to the point that I am considering returning the watch. The principle purpose for the purchase was the heart-rate functionality.

Please advise.
  • Here's another very similar graph from my most recent workout. You can see the similar behavior at around 5:30 lasting for about 2-1/2 minutes.

    This is the warm-up phase of the workout. The heart rate should be gradually raising. There is no pause which would cause my heart rate to suddenly drop. The drop from 128 to 68 is very quick (only 30 seconds). It eventually falls to resting - 58 ! - then jumps back to 145 in less than 1 minute. This behavior is basically the same failure mode as the previous
  • After some reading, it seems like this could be related to perfusion at the point where the body is redirecting blood to a different layer of the skin as a result of a body heat threshold being reached.

    If this is really the cause, it seems like this could be calibrated for each specific activity (possibly a profile generated) to calibrate the device to understand this phenomenon.