HR jumps at the begin of activity Beta 24.10

Dima said:

I have a similar issue on 24.12. My 955 is using OHR while connected to a chest HRM.

Is dynamic source switching enabled? (It's on by default)

If so, your watch may be inappropriately switching to OHR at the beginning of work intervals (or an activity). I've seen this myself during intervals. I'll be wearing a chest strap, and my HR will be slow to change at the beginning of an interval (after I was resting from the previous work interval). But when I look at the data from both external HR and wrist HR after the fact (see below), I can see that wrist HR lagged behind external HR by a few seconds, but the watch decided to use wrist HR anyway.

If this is a problem for you, I would recommend turning off dynamic source switching:

https://support.garmin.com/en-CA/?faq=Nf8r6ApX4d9lX0G0flEsVA 

---

More details:

You can double-check whether this actually happening:

- Open an activity with the issue in the Connect website: connect.garmin.com

- Click gear icon (upper right corner) > Export File. This will download the original fit file in a ZIP

- Open fitfileviewer.com and select the ZIP you just downloaded

- Click on Charts

- Here you will be able to select up to 2 metrics to display on the graph. If source switching was enabled, you will see the following 3 metrics:

-- heart rate (the HR actually used by the watch during the activity, which is displayed in Connect). This could be either OHR or external HR, at any given point in time

-- external hr (self explanatory)

-- wrist hr (self explanatory)

By graphing different combos of metrics, you will be able to see if and when the device switched from external hr to wrist hr and vice versa.

e.g.

- If you graph "heart rate" and "external hr", you will see when the activity hr deviated from external hr. Then you can switch to "heart rate" and "wrist hr" to verify that the activity hr indeed switched to wrist hr at the same points (but ofc it would, because there's nothing else for it to switch to)

NOTE: dynamic source switching is not the same as the watch using OHR when there's signal drop outs from the external HR. This always happens, no matter what.

With dynamic source switching:

- only certain Garmin chest straps are supported

- if the watch decides that the data from the Garmin chest strap is bad, it dynamically switches to the OHR. But during this time, the watch is still receiving data from the chest strap.