# Calculating LTHR

I did Joe Friel’s 30 minute flat out test to find my LTHR (last 20’ average) a couple of years ago, and have used the number ever since — 181bpm.

But recently I was flicking through last season’s races and noticed my HR quite high during several TTs.

I did three 25s (one slightly shortened):
55’ — 180bpm avg — last 20’ 185bpm
56’ — 185bpm avg — last 20’ 189bpm
46’ — 185bpm avg — last 20’ 187bpm

I also looked at the 10s:
185bpm
187
188
190 (3 times)
191
194

Last weekend I did a 20 min max effort on the road bike and averaged 183bpm at 110% of my FTP (set by the ramp test two days ago).

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That is interesting. Zone 2 as 80-90% of LTHR seems strangely high though. For me that would be around 72-81% max HR. I think Coggan has it as 67-85% of LTHR, which works out as 60-75% max HR

80-90% LTHR is pretty much my Friel zone2 HR:

And yes, the Friel zone2 HR is wider than Coggan zone2 HR.

I’ve never used HRmax to calculate zones.

Also, the TrainingPeaks support article on thresholds states:

• Heart Rate Threshold - All Sports: We suggest a threshold increase if your peak 60 minute, or 95% of your Peak 20 Minute, Heart Rate is greater than your currently set threshold.
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I use Intervals.icu for my LTHR. It calculated mine at 183bpm after I averaged that for an hour long TT back in September. Interestingly (for me at least) they calculate my max HR to be 199bpm, I think based on Friel zones. I lowered it after my birthday a month back to 198bpm

Where does intervals.icu calculate your LTHR?

After you do a effort (IMC the hour long TT) if you’ve improved LTHR it will tell you. You can then manually update your LTHR in the settings. There may be another way @davidtinker may be able to help you out there.

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Thanks. I’ve only recently started using Intervals.icu but when I went back there was that note on the file.

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