guided test treshold not detected

DaKo said:

1. Is my expectation of an even higher LTHR plausible? Because I read that the LTHR should be somewhere the pace/heartrate that one could run for about an hour. Which I did in the half marathon.

Typically, the pace you achieve in your 10k PR, if steady, is your LT pace. 

DaKo said:

Running it says maxHR at 209bpm, while I always put in 194

A change in the HR Max can lead to an inaccurate reevaluation of the LTHR during the test. Make sure HR Max is correct, and disable HR Max autodetection. If your doctor lets you, do a field HR Max test.

DaKo said:

So does accepting a new LTHR after a test, also change the maxHR?

No, unless a new HR Max was detected during the test. Disable HR Max auto-detectioin.

DaKo said:

ANd if so, what happens if I accept the LTHR of 177bpm, and manually change the maxHR back to 194?

I recommend you then do a new LTHR test. In my experience, if you decrease your HR Max, your next LTHR test will find a lower LTHR, and vice-versa.

I see some contradictions. I decreased the set HRmax from 209bpm to 194bpm, which should be pretty realistic.

My LTHR is increased to 177bpm, but you say after a new test it probably drops.

Based on my 15km distance in 4:45 steady pace, and my 10km pace of between 4:20-4:30, My LTHR pace should definitely be much faster than 4:58 it detected yesterday.

By the way. I switched of autodetect a few months ago, so that is why I was surprised to find 209bpm as HRmax in Connect. And I set the zones as a %LTHR. Why should the HRmax be of any importance then?

The above doesn't make sense, right?

DaKo said:

but you say after a new test it probably drops

Keep in mind that there is always a rate of error with the Garmin metrics. It means that between 2 measurements, everything else being equal (fatigue, fitness, weather, HR Max, etc. etc.) you will not necessarily find the same LTHR. Garmin doesn't say what is the error rate of lactate threshold HR. For VO2 Max, the average error is around 5% and increases if the error to the true HR Max increases. So, assuming the dependency on HR Max accuracy translates to the LTHR detection. you can expect a similar behavior. 

We also know that when a LTHR cannot be detected, Garmin recommends to lower the HR Max to help with the detection.

"An accurate maximum heart rate setting is also required to obtain an accurate lactate threshold estimate. If the maximum heart rate setting is too high, the test will be too difficult to complete. If it is too low, the test will not record the lactate threshold"

https://support.garmin.com/en-US/?faq=8buMedvX4x6ML5yb9rL5bA

Therefore, it is safe to assume that changing your HR Max will have an influence on the LTHR detection and its accuracy. It is also safe to assume that a change of a couple of bpm in LTHR is within the range of fluctuation due to the algorithm error rate. 

So to be clear, the LTHR can vary between 2 tests even if everything else is exactly the same, which is never the case. It might go up or down by a couple of bpm.

Here is my recent personal experience (which is a case of 1): over the last couple of months, I took down progressively my (olidsh) HR Max value based on my anaerobic workouts and 5k races. I am talking about 1 or 2 bpm everytime. Everytime I did so, my LTHR stayed the same or decreased by 1 bpm after a test, but my LT pace/power didn't change. My biking VO2 Max decreased as well, maybe a point for every couple of bpm, while, surprisingly, my running VO2 Max didn't change.

This might be different in your case, the conditions of your testing, etc.

DaKo said:

My LTHR pace should definitely be much faster than 4:58 it detected yesterday.

Talking about LT pace now, yes it is commonly accepted that your pace for a 10k or even a 15k should be very close to your LT Pace. I doubt that the watch is taking the pace corresponding to the LTHR value at the moment of detection, but it is possible. I think that the watch is using a relationship model between filtered HR values and pace values from your recent training history and the test itself to pick the pace value at LTHR.

This model that tracks the typical output (pace) for a physiological cost (probably a proxy for ventilation based on HR and HRV) over a period ot time is used in various places (VO2 Max, Performance Contion, Stamina, Anaerobic EPOC/TE, pace targets for workout suggestions, etc.). 

For this model to be accurate, you need to feed the watch with good data (hence chest strap, GPS/pod pace, flatish terrain, ...). Once the quality of the data capture is ensured, you need to perform maximal efforts for different interval duration. A simple way to do that is to follow the daily suggestions and from time to time, instead of just following the pace target, run as fast as you for these intervals, but in a steady way. BTW, this is how I monitor my HR Max when I do a maximal effort anaerobic workout.

While the beauty of Garmin algorithms and metrics is that they work well even with sub-maximal effort, if you want the best accuracy, you want to give actual performance data insteady of letting the watch predict it (for example, pace at LTHR or pace at HR Max).

DaKo said:

I suspect daily suggestions use the training zones based on %lthr

I talked to Garmin support and they confirmed that the targets are based on % of VO2 Max, not LTHR. With this in mind, there are 2 open questions. How is the % of VO2 max (ie target ventilation, ie target HR) selected, and how is the target pace selected... The duration of the intervals/workout is yet another dimention and is taken into account since the watch can predict the training effect of the workout.

So, there is a risk that your pace target could be biased for a couple of reasons: a biased VO2 max and/or a biased ventilation/pace model. 

You cleared up risks of a biased VO2 Max by confirming your HR Max and ensuring good data capture. A biased ventilation/pace model could stem from running too many slow/fast workouts, or running on hilly terrains.

From all of the above, it looks like the suspect could be your pace at LTHR. You could test this by running max steady pace for 20mn and take 95% of that speed.