Massive Heart rate inaccuracy when connecting to Concept2 PM5

I have a concept2 rower with PM5. The Garmin devices I use are the Fenix 6X Pro and HRM-dual chest strap.
When I pair the HRM to the PM5, and initiate a workout both on the PM5 and my Garmin watch (row activity), the heart rate displayed on my watch and the PM5 are completely inaccurate. It always shows my heart rate steadily increasing until it reaches 199bpm over a 10min time period, then over the next 10min it steadily decreases until it finally reads accurately. I definitely cannot sustain 199bpm for 20min!! (I wish?)
What is going on here? I have tried pairing the PM5 to the HRM-dual using both options that appear on the PM5 (it shows up as HRM-dual, and also as ANT). Both initially display the proper heart rate when I am pairing, but as soon as I start the workout on the PM5 and the Fenix 6X, the inaccuracies begin.
Can anyone please help me sort this out?
Thank you!
  • I am not familiar with Concept 2 at all, but have you considered not pairing your HRM to the PM5, and pairing with the Garmin only, then I think you will be able to re-broadcast your heart rate to the PM5?

    Intuitively though, I can't see how a connection to the PM5 can break the heart rate somehow...

    One thing to point out - did you make sure you wet the back of your HRM strap first? Not doing that can cause odd behaviour, and as you say it improves after 10 minutes, maybe sweat is providing the moisture you need for a reliable connection and this is why it settles after this time...?

  • There may be problems with heart rate strap. My HRM did kinda the same thing in the past. It gave accurate HR when I first wear it but it started to give higher values reavhing 205 and later down to the right HR value. I just bought a different HR strap from Decathlon and just uesd it's strap with Garmin's HR module. It's working fine.

  • Hi, thank you both for the response. The HRM strap works just perfectly without pairing my fenix to the PM5, so I don't think the strap itself is the problem nor wetting it (though I do anyway).  It's as if there is interference with the ANT+ connections between the fenix, strap, and PM5, but I thought that was one of the main points in using ANT+ vs bluetooth connection.  

  • but I thought that was one of the main points in using ANT+ vs bluetooth connection.  

    Bluetooth is a 1:1 connection, ANT is 1:many so I'm struggling to see how pairing to the PM5 can change what your HRM is broadcasting, your PM5 is just a passive listener. 

    What is going on here?

    Absolutely no idea!

  • I have used a Concept2 rowing machine with PM5 several times per week for years with a dually connect HR-strap. Garmin standard HR-strap, HRM-Run and Polar H10, both using BT and ANT+. The only problem I have is that the PM5 looses connection to the strap quite often, but I do not experience any strange behavior of HR measurements. I also do dual connection to the SkiErg, but that is the same PM5 module.

    I did experience odd HR measurements years ago, using Suunto and Polar straps, but that was usually an indication of end of life for the strap.

    I do know, that some ppl have experienced problems using some materials in their clothes, relating to static electricity.