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HR zones in activity display (both GC app and web) do not match zones on device

Hi,

I'm experiencing the following very strange behaviour.

I have a Forerunner 735 and since Dec 27th all activities (3 runs and 2 rides) are shown with time spent in HR zones where the zones are wrongly defined.
This is consistent between GC app and web.
The device has HR zones defined as % of lactate threshold which is 162, so zone 5 on the Forerunner starts at 163 and this can be seen directly on the device and also from GC app and web checking the device settings. 
But in the activity display the HR are different: zone 5 starts at 172 and all others are shifted upward accordingly.
This is true only for my last 5 activities (non counting swims as I'm not using a HR band), before that everything was fine.

I didn't touch anything, what went wrong?!
Thanks for your help
Davide

  • As stated at https://www.garmin.com.my/minisite/runningscience/ "Select Garmin devices can detect your lactate threshold either through a guided workout or automatically during a normal run". If your watch indeed supports the LT detection, it is likely that your LT was automatically detected and hence different than the HR zone setting currently shows.

  • Thank you for your reply. I thought about that. I did a guided workout once (2 years ago?) and that's where the 162 comes from. yes LT automatic detection has always been on, although I have no idea how that works, and it never changed the threshold value shown on device.
    Supposing that's nevertheless the case, why is this not actually redefining the zones but is only used in the activity display and never shown anywhere? in other words the discrepancy between the two screenshots I posted above still cannot be explained.
    what do you think?

  • Well, you tell the value never changed from 162, but on the screenshot you posted, there is 163, so it looks like it is not always the same.

  • my mistake sorry. the value has always been 163 not 162.

  • what can have happened is that my measured maximum HR increased, but still that doesn't explain why the two screenshots are inconsistent. it looks like a bug to me.

  • OK, in that case I do not know, why it changes in the activity and not also in the settings. But if you want keeping it fixed, click the pencil icon, above the settings, select a different method than the LT, and set the HR zones manually in the way you wish. You can also do it separately for the running and bike, if you wish.

  • It worked, thanks! Still don't know what happened but I did as you suggested, chose the HR reserve method and then I put in by hand the same numbers it previously found automatically as LT fraction. Then went for a ride today and the zones now match :)