Do you think Garmin’s Lactate Threshold Measurement is Accurate?

No.

Any metric that depends on HR is going to be inaccurate if you solely use wrist based HR.

Any metric that depends on HR is going to be inaccurate if you solely use wrist based HR.

Any metric that depends on HR is going to be inaccurate if you solely use wrist based HR.

Yes, it is fine, but it requires accurate data.

(1) You must have a fairly accurate (within a couple of beats) Maximum Heart Rate entered into the watch. That has to be a value you ascertained through measurement, rather than being calculated from a cookbook formula.

(2) Your acquired heart rate data, in all workouts, needs to be accurate. That will typically require a strap, since wrist heart rate measurements under vigorous activity is not accurate enough.

Once you get a correct Maximum Heart Rate (HRmax) entered in the watch, and you take accurate heart-rate data with the use of a strap, you can then compare how the Garmin estimate compares with your running steady pace at 87%-90% HRmax. You can run threshold workouts, keeping the max heart rate below 89% HRmax, and be fine.

No, it's not accurate. I use a strap (for workouts anyway), and I've never seen a value that was as high as my marathon heart rate.

That said, even a step test in a lab is not very accurate. They aren't actually confirming the pace where you hit maximum lactate steady state. They just plot a curve (with only a handful of points), and project where they think it is. That method works for comparing curves over time, and it will give you a ballpark threshold value, but any serious athlete can probably guess their lactate threshold with similar accuracy.

This needs clarification, as to whether you are referring to your average heart rate in the marathon, or your maximum. Due to cardiac drift, training status, effort over the distance, marathoner vs 800m type athlete, etc., I can’t recall any source citing max heart rate in a marathon as being lactate threshold heart rate.

LT2 pace is typically cited as the pace one can sustain for about an hour. Therefore your original comment is not making much sense.

My Garmin currently indicates my LT2 heart rate is 88% HRmax.

Of course not. It's tech entertainment.
People like to be suckered into the feeling that their stupid little run meant anything.

In my experience using a chest strap, the Garmin watch is almost spot on for LT1 and a few BPM low for LT2. This is comparing to taking LT readings with a meter. That being said I haven't done a max HR test and just put in a max HR I saw a few years back so potentially so room to improve.

You are right but I will be devils advocate here. ANYTHING you do short of blood draws is guess work. Pace, Effort (RPE), HR. So, in my mind, most of 98% anyway don't poke our fingers, so one more data point is fine with me. As always, RPE has been found to be fairly accurate, and when you back it up with pace (depends on weather etc...) and HR (depends on accuracy, weather etc...), its like triangulating the right workout for threshold. I use all 3 sort of. If the HR is close and the effort (RPE) feels right and the pace is semi right from the tables, you are pretty dam close.

My average marathon heart rate. As in: I can run for multiple hours at a heart rate higher than Garmin thinks my lactate threshold is. In fact, Garmin will sometimes give me a new lactate threshold after a marathon or a half marathon, and it will be lower than my HR for the entire race, bar the first few minutes.

I wish the benevolent dictators quickly locked down all posts following this lol

I don't like either of those papers. DMax and DMaxMod are only math constructions and often do not represent MLSS. So, correlating anything with DMax/DMaxMod is weak.

Actually blood draw has some shortcomings and measurement errors too. And this is of course aside from wide individual differences

HRmax also best described as HRpeak since it’s activity, protocol, day to day, training status, duration and environmental dependent.

Interesting these companies have trouble admitting they are estimating rather than measuring. For most athletes and workouts RPE is preferable

This is probably the best approach outside of a lab scenario. One thing I think most people misunderstand about the different training paces is that things like threshold, V02 max, aerobic/zone 2, etc. operate on a continuum. They are not on/off switches. I.e. a threshold workout will also help build your V02 and your aerobic capacity, just not as efficiently as a dedicated VO2 or aerobic workout on their own. And, if you're V02 pace for 1200m repeats is 3:45, but you can only muster 3:52s that day (for whatever reason), then it's not like you suddenly got no V02 benefit out of the workout. Similarly, if you're in the ballpark for threshold based on RPE, and your HR is 86% instead of 89%, you're still getting most of the benefit. I primarily encourage my runners to use things like pace predictions and HR to "calibrate" their RPE, and as a sanity check against RPE during or after a workout for this reason.

All I ever hear from people is "easy is a feeling not a pace" but then the same people say "what is your threshold pace?"

No type of running should be based on a pace. It should be an effort.

If I ran based on feel I’d never do it