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hart rate zones suddenly changed drastically...why?

Today went for a run in Garmin hart rate Zone 3.

After a few hundred meters I was already way to high in Zone 4.

Apparently the watch changed the zones but also really drastically (Zone 3 and 4) without warning or indication.

Zone Before Now
5 >162 > 158
4 154-161 140-157
3 144-153 123-139
2 130-143 105-122
1 105-129 88-104

Only indication I have is that the watch said it updated Bluetooth drivers on the watch.

Anyone have an idea why the watch did this (FR 945)??

  • The watch defines zones as either % of max hr or % of LTHR. If either of these changed, then it would also impact HR zones. Another explanation would be change to HR zones in Garmin Connect.

  • Do you have it set to detect max HR?

  • Just checked some more....

    Apparently it was first set to assess hart rate zones on lactate threshold.

    But somehow switched to max HR which gives totally different zones.

    So now it should be back to the zones that i expected

  • Had exactly the same with my 935. Seems my zones have all changed and my watch has decided to try to kill me! I have just added my old values back in it….. did notice my max heat rate was way too high as well. I always use %of lactate threshold it’s definitely changed.