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Dynamic source switching

Bitti
7 days ago

Some people here have expressed their doubts on whether the heart rate Dynamic source switching is ever useful and have labelled it as a useless feature.

Reently I ran a DSW run with a 10 minute warm-up, some intervals and a cool-down. I used a HRM Pro+ which I wetted before the run. After the run I used FitFileViewer to check the fit file, since I had used the strap for pace and wanted to compare it with GPS pace, but no surprises there. However, I noticed a huge gap in breathing rate, and that made me check strap HR vs the HR used for the activity. And it seems my HR strap had been giving totally bogus numbers for the beginning of the warm-up - an easy steady-state run, but the watch had noticed that and used wrist HR for those portions, which clearly was the right thing to do. Screenshot below.

And I'm not saying that there wouldn't be examples where the watch incorrectly chooses wrist HR over strap HR. Just that Dynamic source switching also does what it's supposed to do.

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  • 0 5 days ago

    and that is a totally wrong behaviour from your watch

    there could be cases where having some kind of data is crucial (such as in races or climbing the Grossglockner once in a lifetime), but 99% percent of the time what you do is training - and bogus data from WHR could completely destroy your long term training data

    there were times when my VO2max was on Olympic level for a while, because the WHR recorded unrealistic low HR and it was very happy to skyrocket my VO2max based on that 

    a proper measurement system in this situation would raise a warning that you have a lost contact / connection with the chest strap, and could ask whether you really want to use the WHR instead

    this auto switch could be okayish on an Apple watch - different demographic, different goals, but on a system where data do matter, this is unacceptable

    garmin did lose the sense of the reality for a while now...

  • 0 5 days ago in reply to pxl
    pxl said:
    a proper measurement system in this situation would raise a warning that you have a lost contact / connection with the chest strap, and could ask whether you really want to use the WHR instead

    This is such a common misconception, but dynamic source switching is not about drop outs / lost connections at all. You can see right on the graph that external HR was available for the whole period where wrist HR was used instead. If the connection had really been lost, there would be no external HR data for that period.

    Dynamic source switching is about Garmin discarding what it sees as bad data from the external HR. That is, it's receiving data, but it thinks the data is faulty. It's worth noting that this will only happen with a compatible Garmin chest strap. (I assume that Garmin chest straps have some non-standard way to tell the watch about the quality of the data)

    Even if you disable dynamic source switching, or you use an older watch which doesn't support it, the watch will still automatically switch to wrist HR if you literally have lose the connection with the external HR. If you want to avoid that, the only solution is to turn off the wrist HR.

    Having said that, for me, dynamic source switching has only ever selected obviously bad wrist HR data over good chest strap data. Like I'm doing intervals, and when I switch from rest/recovery to active running, the wrist HR lags behind external HR for a few seconds, but during that period of time, source switching decides to select wrist HR. It's obviously wrong in hindsight, unless my chest strap has the ability to predict the future and incorrectly show me data that's a few seconds ahead.

    I think it's a shame that Garmin tied dynamic source switching to recording both external and wrist HR to the FIT file. (If you turn off source switching, then the device only records the HR values that were used during the activity, just as before dynamic source switching existed)

    Obviously it's not meant for the end user, but it is interesting to look at. It seems that the only way to get the extra recording without any actual source switching is to use a 3rd party chest strap (since Garmin says that source switching only works with Garmin chest straps)

  • 0 2 days ago in reply to FlowState
    FlowState said:
    Dynamic source switching is about Garmin discarding what it sees as bad data from the external HR.

    sure, we are talking about the same thing.

    bad quality data is usually generated due to the contact got lost between the body and strap and the user must know that there is something to fix (realign the strap, make it tighter, etc.)

    again, I don't want to look like a broken record, but this is a system that is dedicated to record data and then to analyse that historically

    as bogus data can make the system unreliable, it must be flagged as is, so that later it can be discarded / corrected / etc. as with garmin you cannot choose the source of data later, the only option is to discard bogus data

    whether the data source is reliable or not, should be the concern of the user - it cannot be presumed automatically that the user trusts the WHR or not (when I grab my chest strap, then I definitely don't)

    with this dynamic source switching, garmin went down the slippery slope of the appleish wordview:

    "everything is fine, you don't need to care / know how to use a chest strap correctly, we are taking care of your ignorance - just buy a chest strap, buy a watch, and the world will become a flowery field with cute little birds singing the Ode to Joy and we'll fill your daily steps circle with some beautiful numbers - no worries!"