Lactate Threshold decreased after running faster??

HR can vary on daily basis, depending on internal (systemic stress, lack of sleep, less glycogen) or external (temperature, wind, hour of the day), and I don't think any algorithm could factor all of them. HR at threshold cloud not decrease suddenly, but pace could. For this reason I started to accept new LTHR measurements in which HR is roughly the same but pace differs (increasing or decreasing). In my specific case, estimated LTHR by F7 is 176 and real one is very close. Pace however is underestimated by 15"/km (meaning that I could handle a faster pace in reality)

Not enough information to be definite.

But certainly improving your aerobic base with a lot of zone 2 running would allow you to run faster at a lower HR, even if your LTHR dropped.

This is actually a good thing, as aerobic fitness is more durable than trying to run faster through training with a lot of threshold based running.

In my experience, the auto-detection doesn't work as well as a LT test.

If I run sprints (30s/30s), VO2 Max (4mn/3mn) or Anaerobic (1mn/3mn) intervals for example, I always get a lower threshold. Both HR and pace can change but HR is never more than one or 2 BPMs down.

With a built-in test, or when running a "true" threshold workout and getting an auto-detection, the LTHR is constant, and the pace gets updated if relevant.

So IMO it depends on the type of run that got you the auto-update, and, of course, the conditions in which you got the previous one :-)

tboooe said:

I would have expected that since I ran faster at a lower HR my LTHR and LT Pace wold increase.

According to the (insufficient) doc of Firstbeat (see graph)

https://www.firstbeatanalytics.com/en/features/lactate-threshold/

LTHR is calculated based on the deflection point of HRV. So it's not the HR and speed data that needs to be analyzed, but the HRV data. I don't know any method to check this out.