Just did a 20 min FTP test today and saw a wopping / surprising increase of my Threshold HR with +2. I had an avg heartrate 6bpm higher than my last FTP test I did a month ago. This brings me to question my HR zones and what algorithm to use for this? especially my Zone 2 ?
In garmin I’ve been using my max HR and resting HR (from my watch):
Just tried to change this to “based on threshold” and I get 153bpm for Zone 2 insted of 142bpm with my “old” model.
I know I know… typically LT1 is not Zone 2 limit but again… when I train endurance rides I would like them to count as “endurance rides” 
Any recommendations here on what to do?
Thanks
When it comes to Z2, lower is better 
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In general, don’t use 20-min FTP test to estimate Threshold HR. I’ve seen some coaches use it, but carefully.
What are you doing?
Intervals has Friel HR zones selected by default.
Friel threshold HR is estimated doing the following:
- solo 30 minute time trial
- do this as if it was a time trial, an all-out 30 minute effort that is evenly paced or as a negative split
- don’t start too hard, and yes, it takes practice to do this correctly (just like 20-min test)
- after 10 minutes, click the lap button
- use average HR of final 20 minutes as your estimate for Threshold HR
Here it is on TrainingPeaks website:
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Thanks for this. I think THR will be a bit lower then 
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