Heart rate zones

My experience is with the F5+ but I assume it’s working the same way with the 935:

I have not done the guided LT test, but usually it registers an update LT when I do a run of mixed intensity - varying between zone 4 and 5. I haven’t found that you need to do this in any structured way as long as you are crossing the LT multiple times during the run.

Note it uses your HRV for this detection so you would need to use a chest strap (not WHR or other optical hr sensor)

Runs of progressively increasing intensity will generally lead to the 935 generating an LHT pace and HR. Is it correct? Unsure. Personally, I prefer to base LT heartrate/pace of a simple, if not tiring, interval workout:

Warm up 15 minutes including some strideouts for 3 or 4 minutes.
Run at the hardest pace that you can maintain for 30 min.
Start timer for 10 minutes.
Start timer for 20 minutes
Cool down for about 15 minutes.

Lactate threshold HR and pace is the average of the last 20 minutes of the 30 minute effort. The aim of the 30 minute effort is to hold a pace for the duration, not go out too hard and fade.

LHT, like most of these metrics, is not something you chase as an acute response to training. It's a chronic response that needs to be assessed at the end of a training program aimed at improving it over a period of weeks.

Is it correct? I guess there could be individual differences, but yes I find the detected value quite consistent with my perceived effort/exhaustion, at least within 2-3bpm.

At least I assume it will be far more accurate than what most people/beginners are able to carry out correctly and then determine/calculate a correct value based on the manual method you are suggesting.

scotthunter2: Garmin's guided test is based on your maximum HR in your physical profile, which makes it a bit of a Catch 22. Have it set too high, and you won't be able to reach the required zones for the test to acquire a LT, too conservative, and you'll end up with a value that is way too low.philipshambrook's approach is standard procedure (CP30) to come up with a 30'-effort needed for an LT reading. It's actually your maximum effort that you can hold for 60' but coaches, and physiologists figured no one in their right mind is motivated enough in an environment for testing purposes to do a maximum effort activity for 60', leading to wrong numbers, so the community settled on an all-out-30'. It's a VERY taxing workout (done on a hard day instead of the workout) and shouldn't be repeated more often than every 4-6 weeks to not interfere with your regular training schedule.

I don’t think you will get a wrong value for LT if your maxHR is set wrong, but it might be more difficult to get a detection because the watch is «looking» in the wrong area. After all, I believe LT detection is (mainly) based on changes in HRV which is a direct measurement and not an indirect estimate calculated from other values.

I don’t think you will get a wrong value for LT if your maxHR is set wrong, but it might be more difficult to get a detection because the watch is «looking» in the wrong area. After all, I believe LT detection is (mainly) based on changes in HRV which is a direct measurement and not an indirect estimate calculated from other values.

Yes, LTHR is based on speed, HR, and HRV but you can easily fail the test by setting the wrong mHR in your Garmin device. I did it in both directions. A non-invasive LT test is based on the HR deflection point, i.e. the point from where HR and speed are no longer in a linear relationship, a.k.a anaerobical work. Set your HR too low, and you won't reach an anaerobic state before the test ends, set it too high, and you won't be able to hold the effort asked by the device's test procedure leading to a test cut short. I tried both ways by decreasing, and increasing mHR in my 935 significantly. The latter didn't produce a LTHR because I topped out well below 90% mHR, and the former couldn't come up with a number one time, and put out a way too low value another time.
Granted, this was with highly unrealistic mHR values, so yes, I guess you're right that you will get a proper value if your mHR is at least in its ballpark, but detection will be much harder. However, seeing how much stress repeated LT runs mean, I'd rather get it right right away, because it really puts a damper on your mood when after 20' of hard running the watch tells you it failed to find an LTHR. That's why I stick to the CP30 method, and don't rely on Garmin's algorithm.

phl0w If someone isn't sure what their Max HR this is, wouldn't setting your Max HR using the 220 minus age be the best case scenario to use for the lactate threshold test? I understand this method is outdated, but it seems to me it would be a happy medium for someone who doesn't know their Max HR without guessing to high or to low.
????

phl0w: Sure, if you deliberately try to throw the LT detection off by setting a very wrong max hr, I’m sure you could manage to fail the LT test or even get a false value.
I agree with TMK17, if you enter a max hr that’s at least in the right ballpark the watch will probably be able to detect your LT, and once that is in place and you base your zones on LT it doesn’t really matter how accurate your Max hr is. If you let the watch handle LT your zones will be based on a real value for your body, and maybe more important: it will monitor it and keep your zones up to date as your fitness level changes.

TMK17 SAHO : That's why I said

I guess you're right that you will get a proper value if your mHR is at least in its ballpark, but detection will be much harder.

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Still, there's an underlying principle why CP30 is the standard procedure for non-invasie LTHR tests: LTHR is a training principle (like VO2Max, VDot) that doesn't rely on one's maximum HR, for good reason, mHR was found to be completely irrelevant for training. That's why I (and exercise physiologists using LT for coaching) have a problem with Garmin's procedure. Not only is it using your mHR as baseline for the incrementally increasing pace/effort asked during the procedure, but in doing so puts your focus back on your (maximum) heart rate. Joe Friel wrote (paraphrasing): If you have the mental and physical capacity left to even think about your heart rate, let alone check your device, you're not going hard enough.
Yes, mHR set in the right ballpark gets you a result, yes it might take a couple tries to actually acquire one, but the whole reasoning behind using LTHR,VO2Max,VDOt and what not is to leave mHR behind and train by pace, and perceived effort. For instance Jack Daniels only put percentages of mHR in later editions of his "Running Formula" because it was asked so many times. But by choosing a pretty broad interval (60-78% for easy runs) he's still saying: your HR doesn't matter, you should run at the pace taken from the VDot tables, and adjust by going 20sec faster or slower depending on your daily condition. Quite incidentally his 78% happens to be about 85% of one's LTHR, which is the upper limit for easy runs, and funnily enough about the same HR the "MAF" method wants you to run at. From a physiological pov it totally makes sense, because those upper limits happen to be right about where your system enters aerobic work (aerobic threshold, your system switches from burning fat to burning carbs), a state you can exercise in for hours. What I wanna say with this wall of text is, that all the different approaches to training work with the same underlying principle: physiology. They use states of rest, aerobic, and anaerobic work (and coin different terms to fit their "method") to base their asked effort on depending on the desired training effect short, and long term. None of this, however, is based on your maximum heart rate.

tl,dr: Forget about maximum heart rate!