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HRM-Run and HRM-Tri HR data dropouts with Forerunner 645

I have a Forerunner 645 (non-music) and recently got a HRM-Run strap to use with it.

The setup works fine for normal running, but when doing intervals I've noticed the HR data drops out frequently during the walking rests between the intervals.

I'm guessing that this is due to the different arm position during the walks, i.e. the arms are hanging straight and the watch is therefore lower down by the side, with the signal between the watch and the strap being intermittently blocked by the torso as the arm swings, resulting in the dropouts. I've swapped the battery for a new one with no improvement.

I got in touch with Garmin customer services about this and they said the unit was faulty, so I sent it back to Amazon, got a refund and bought the HRM-Tri instead (same price - I realise the data caching of the Tri will not work with the 645). I've just been out to test it and exactly the same problem occurs!

Is it unrealistic to expect an uninterrupted signal between the strap and the watch if it has to intermittently pass through the body, or could there be a fault with the 645?

  • Odd, I've been using the HRM-Run with my 645noM for 3 months and have never experienced a dropout. Just the once I thought I had, but it turned out Garmin Connect graphs scaled the Y axis starting not at zero but at 140 bpm for that activity.
    Bear in mind I've not run intervals. Does this only happen when you do?

  • Yeah normal running on the flat is fine, it only disconnects when I stop running and walk for whatever reason (rests during intervals or trail running going up a steep hill). If I keep my arms up while walking, i.e. elbows bent at 90° as if still running, the disconnects don't occur because the HRM module and watch remain in line of sight and are not blocked by the torso. It's only when I straighten my arms to a normal walking swing that the disconnects occur occasionally.

    I've tested this by deliberately holding my watch arm behind my back and this always forces a disconnect after a few seconds.

    I'm wondering if the connection from the HRM-Dual would be any better. Does anyone know if it connects to the watch by BLE or ANT+, and would this make any difference?

  • I'm fairly new to my HRM-Dual, but it appears that it is connected via ANT+ to my FR645. I do not see a method for connecting via Bluetooth.

  • Do you get data dropouts when walking with your arms swinging by your sides? And can you force it to disconnect by holding your watch hand behind your back?

  • I've experienced no dropouts in the month-and-a-half I've had mine. That said, I've also not used it while walking everything has been at a run. I can try this on my next run.

  • On my run this morning, I kept my hands (watch) down by my sides during the warm-up phase (a brisk walk, arms did move but not up like when running) and then again during my cool-down phase. I do not see any drop-outs in my heart rate graph during any point during the warm-up, run or cool-down.

  • Hi. I had same problem this morning with my 935 and HRM Tri. Dropped every 30sec or so while riding. I was wondering maybe its because i started using bluetooth headphones and phone was in my back pocket. Also had it during my last race in April on the run. 

  • OK, thanks for the feedback. I've sent the Tri back and ordered a Dual.

  • So I've had the Dual a few days now and done several runs with it, including intervals and trail runs with walking involved. I've seen no data dropouts at all, like I did with the Run and Tri. It seems these two have a flaky signal compared to the Dual.