failed guided Lactate Threshold Test

Make sure you do the test on a route that doesn't have uphills or downhills (a running track preferably) and start each test step at the lower end of the hr range, then accelerate steadily so that you are at the upper end of the range at the end of the step. Following those I've had no problem getting a successful result.

The manual gives some info on how it works and gives some tips: www8.garmin.com/.../GUID-3ED97FFE-025E-47EA-9C70-DD86156617BD.html

It's good to have a bunch of prior runs with the watch and you may need to manually lower the max HR.

Try to set your max HR a 5-8 beats lower as estimated/formula calculated. To get your score you need to do a steady pace minimum for 4 minutes on your VO2max HR (yes, it is hard).

global_local said:

To get your score you need to do a steady pace minimum for 4 minutes on your VO2max HR

This is not quite correct.

Yes, you need to keep your pace steady during *each* phase of the ramp. Your HR will increase during the first minute of each step, should stabilize as your ventilation meets the needs (or not), but might increase todards the end of the interval.

But you don't need to reach your VO2 Max HR to get a detection. Maybe global_local is referring to zone 5 (unfortunately often called the VO2 Max zone). In that case it is possible that your HR will get into zone 5 towards the end of the test, but not necessarily: the threshold might be detected earlier during the interval before the last one.

It is more important to keep a steady pace that keeps the HR in the target zone in general than changing your pace to try to accelerate the HR or keeping it into the zone. As, a bit unfortunately, you repeat the test. you'll learn what steady pace you should keep during each HR goal interval. For example, using a pace slighlty below your previous treshold pace as a target , then slightly above, the significanlty above for the last intervals should help (assuming it was not off to start with).

global_local said:

Try to set your max HR a 5-8 beats lower as estimated/formula calculated

This is right, a failed test might be because the HR Max is not correct, either too low or too high.

It could be so low that the HRV trends the watch is looking for do not happen. Remember that LTHR is around 90% of Max HR. So a 10% error too low would prevent the observation of the expected HRV trend changes.

If could be so high that you don't get your HR around 90% of Max HR during the test and the watch is still waiting for the HR to be close enough to 90% to validate the changes in HRV.

Yes, another explanation is that there is an issue with your chest strap. If you can complete a stress test with your chest strap, it would be a good sign there is no issue.

Finally, I recommend you run a new test whenever your change your HR Max, as both reflect dynamics in HRV as you ramp up your efforts.

What kind of strap were you using? My FR955 will let me run the guided lactate threshold test with my Coros arm strap (optical HR) but I haven’t been successful in actually getting an LTHR reading this way. It has only been successful when I use the HRM Pro+. 

Optical HR sensors don’t provide valid HRV data (required for the test), including external optical HR sensors: https://www.dcrainmaker.com/2023/07/coros-heart-rate-monitor-optical-band-in-depth-review.html (search for “HRV” or jump to the product comparison table)

I remember reading that the Scosche optical armband sends HRV data to the watch bc the standard demands it, but the data isn’t actually useful or valid. I assume the same would be the case for any other external optical HR that can talk to a Garmin.

So your watch may let you run the lactate threshold test because it can’t tell the difference between a strap that provides good HRV data, and an optical armband that provides invalid HRV data, but the lack of good HRV data causes the test to fail anyway.

It seems to me that the only relevant difference between the watch’s optical HR and an external optical HR is that the latter pretends to provide good HRV data and therefore tricks the watch into thinking an LT test is possible.

I figured it was something along those lines. It’s too bad because I much prefer the Coros arm strap to my HRM Pro+.

I did wonder if trying to move from bottom to top of range in each section was the ideal.   That may be too nuanced for me to accomplish.  I was briefly over in a early interval, and then flagged for not moving into range quickly enough in the 4th of 6.  

Thank you for the suggestions.  I am going to fiddle with MHR first..