Lactate measurements for AeT confirmation?

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  • #26250
    Øistein Thomassen


    First time poster here. Firstly, many thanks for providing this fantastic website which is packed with valuable information!

    Just a question regarding lactate measurements and AeT that I hope you may be able to address. How closely is lactate correlated to AeT and RER? Will lactate start to increase as soon as fat burning levels out and the body starts working harder to obtain ATP from glucose (50/50 metabolism)? Or could lactate stay low even at even higher RER (RER approaching 1.0)? I’ve done a bit of lactate testing during running recently with the following readings:

    0.8 mmol/L at 140 bpm
    0.9 mmol/L at 150 bpm
    1.0 mmol/L at 160 bpm
    1.5 mmol/L at 166 bpm
    1.7 mmol/L at 170 bpm
    2.6 mmol/L at 173 bpm
    4.0 mmol/L at 180 bpm

    From the lactate readings, would it make sense to conclude that fat burning reaches a plateau at 160 bpm (lactate 1.0 mmol/L) as the lactate curve is completely flat up until that point after which it increases quite quickly? In case, I’d reckon that my optimal aerobic zone would be 150-160 bpm? The confusion is that this is much higher than the calculated MAF heart rate which is 136 (I’m 44). Mafftone seems very strict on not deviating from the calculated HR unless you’ve done a VO2max test showing the actual RER. Let me add that my AnT is around 185 bpm (Joe Friel method) and I am able to nose breath up to that point.

    Thanks for any input 🙂

    Best from Norway,
    Oistein Thomassen

  • Participant
    Dada on #26271


    Looking at my lactate threshold test, I would suggest that your AeT is 165. My lab defined the AeT as followed:

    First lactate point where the concentration increases by at least 0.4 mmol/L. Then interpolation. So from 160 to 166 we have an increase of more than 0.4. Interpolation yields then 164.8 bpm so 165 bpm.

    Best regards

    Øistein Thomassen on #26306

    Thanks for your reply dada. Do you know how reliable this is compared with doing a VO2max test (which from my understanding is the only test which really give you the correct values? Could it be a theoretical possibility that my fat burning levels out at 150 even though lactate doesn’t start to rise before 160+ hence overestimating the HRfor fatmax?

    Scott Johnston on #26366

    A maxVO2 test is in general not a good method for determining AeT and this is explained in this article

    A gas exchange test is still the best method for finding AeT (where the stages are at least 3 minutes long).

    For years I have used blood lactate tests though and have gone by the commonly held definition of finding the HR where the lactate concentration has risen by 1mMol/L above its lowest level or when it reaches 2mMol/L.

    The MAF formula is not going to work for everyone. It may have high statistical significance in a large population but it may not tell anyone individual what the proper AeT is. It clearly is wrong for you. With lactates as low as yours are I can say with a high degree os certainty that you are a slow twitch muscle fiber dominate athlete and probably with many years of aerobic base training behind you.

    If you determined your AnT/LT to be 183 and your lactate is at 1.7 at 170 that too indicates a high AeT relative to AnT which suggest a high level of aerobic fitness. I would be inclined to use 170 as the upper limit of Z2 but you may find that this is too intense for a lot of your aerobic base training and you need to limit the amount of time spent form 165-170 and do more Z1 training coupled with more Z4. Z1 will be about 140-155.


    Dada on #26368

    Oistein Thomassen:

    Did you do the test fastened? The problem with fastened lactate tests is that your lactate is way below well-nutrioned tests. In my fastened test, I have reached +1.0 mmol/L (from lowest value) above my AnT whereas the +0.4 mmol/L increase yielded 153 bpm which corresponds well with hr drift test and mouth breathing.

    Can you give us more information about your endurance history?


    Øistein Thomassen on #26465

    Thanks for the clarifications Scott! I’ll do the 5% test as well to get an indication of the cardiac drift at different heart rates. Probably starting around 160 bpm (outdoor test).

    Your comment “high level of aerobic fitness” is obviously very flattering but from my point of view quite far from the truth. Anyways, I’ve decided now that I’ll be consistent in the coming weeks and months and do lots of zone 1-2 running.

    I’ve been training quite regularly over the last 8 years, however the volume would probably be considered (very) low by your standards. Over the first years I mainly did mountain biking, switching to running some 4 years ago. My heart rate has always been quite high though – during Ultrabirken 2015 in Norway (9+ hours, 133 km mountain bike race which you might have heard of) my average HR was 164 (and often in the 170 range). That’s probably also indicating that my AeT is around 170 for running i.e. the same as you conclude based on the lactate readings. 170 indeed feels slighly more intense than 160-165 however, the only risk of injury or overtraining is if the volume is very high, isn’t it? And if I feel quite ok the next day and the resting HR is not increasing, there is no worries when it comes to just keep on running in the 165-170 range?

    Dada, the lactate readings are actually merged from several runs with different intensities, however the curve seem to be quite consistent when I add new data. Usually I’ve eaten a couple of hours before the run.

    Thanks again.

    Øistein Thomassen on #26538

    Just wanted to add that I ran for an hour yesterday in flat terrain. I tried to keep the heart rate around 160. The Pa:Hr (TP) turned out to be 3,82%. That should suggest that I haven’t crossed the AeT? However is it worth trying to push it up to 5% going for a slightly higher heart rate? FYI the lactate reading was 1.0 mmol/L 2-3 minutes after the end of the run.

    Scott Johnston on #26555

    The difference between 3.82% and 5% is too small to worry about. I’d use 160 as the top of Z2. This will vary from day to day by several beats anyway depending on your recovery state.


    Øistein Thomassen on #26559

    Just want to add that I performed the same test today but at approximately 170 bpm. Pa:hr = 5.26%. Quite surprised that the drift wasn’t that much more than at 160 bpm although I can certainly say that it felt a bit harder. However would that really be regarded as zone 3 considering the result from the today’s test result?

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