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Garmin HRM PRO Power Readings

micro
over 1 year ago

Hey, I have been using this strap with my Epix for quite some time in an On and Off fashion. What I have noticed though is that the power readings for the strap are constantly higher than the ones from the watch. I had 3 epixes during the last year and they all read more or less the same. That is why I am thinking the HRM is the culprit. What is your experience with this combo? 

  • 0 over 1 year ago

    Welcome to an issue that cycling power meter users have been aware of for some time - measuring power in different locations will produce different results. 

    I agree with of sticking with just one location, so that you have you have data that is at least internally consistent.

    It's good to note your different devices measuring about the same in the same location.

  • 0 over 1 year ago in reply to Etupes25

    Yesterday I learned on another thread from  that the watches use the pace provided by the HRM Pro as help if GPS signal is weak (even if HRM Pro pace is set to "indoors only"). That might also affect the pace and power differences for wrist vs strap. (The only way to find out would be to run with HRM Pro pace set to "never", then only GPS pace should be used for both HRM and wrist pace.)

  • 0 over 1 year ago in reply to Bitti
    Bitti said:
    Because remember that HRM Run, HRM Tri, and the Running Dynamics Pod don't provide any step-based pace, and they can be used to provide running power.

    Yes they can, because they also provide running dynamics which mean they have all the sensors for a power model.

    The same applies to a Stryd Pod. It uses 3D accelerometers and a gyroscope to estimate power, pace and distance and similar running dynamics metrics.

    When you use the watch wrist power and pace and compare to the HRM power and pace, you can see how the pace estimation difference explains the power difference. The same limitations in terms of accuracy apply to the pace and power models.

    Even with similar sensors, it is harder to estimate power or pace from the arm than from the body, and harder from the body than from the foot. This is the point you make earlier.

    i don’t know what level of data is streamed from the HRM Pro to the watch. Is it sensor level data (I mean at the accelerometer and gyroscope level) and the watch is calculating pace, power, stride, ground contact, etc or is it at the user/fit level and the strap is sending pace, power and each running metric (then it would behave like a Stryd Pod)?

    An argument in favor of sending basic sensor data is that the watch could use the machine learning chip on board to support more individualized models. 
    Maybe some CIQ developer has more insight.

    At any rate, I doubt that the pace data is an input to the power model, but is highly correlated for physical and sensor sharing reasons

  • 0 over 1 year ago in reply to Bitti
    Bitti said:
    Even Garmin's own running power page (https://www.garmin.com/en-US/garmin-technology/running-science/running-dynamics/running-power/) says "Speed from the watch"

    This article indicates that the power model uses “the speed on the watch” combined with the running dynamics from the strap.

    This is not consistent with my testing since I was using either the pace from the watch or the pace from the strap and the results were very different, running on a treadmill at constant pace, without GPS, and explained by the pace difference. This pointed to the fact that running dynamics, unlike pace, are very similar between the watch and the strap in these conditions (although there could be a notable difference on more varied paces and elevations).

    So the question remains: does the power model use the same pace data as the source selected for pace, or does it use the pace data produced by the source selected for power?

    i will test this out by using the Stryd pod for pace and see if the power variations are still the same.