UC Davis Metabolic Test

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  • #55077

    I went to see Judd at UC Davis this morning for the metabolic efficiency and lactate test. This is the “slow build” test. Not seeking VO2max. Just the first ventilatory threshold and endurance-pace training zones. And substrate utilization.

    After a 20 minute self-selected warmup, the test was started at ~13:20 min/mile pace (walking). Every 4 minutes, a lactate test and increase speed 0.5mph. I walked the first two intervals and then started running. Stopped after 4 minutes at 7:30 pace. Which is about as fast as I ever run doing intervals.

    Computed first ventilatory threshold (first lactate lift above 1mmol) at 142bpm and 9:19 pace. That is consistent with what I feel running. That’s the level at which I feel I’m starting to work just a little instead of simply cruising.

    At baseline lactate, plus 1mmol, I was at 148 HR and 8:42 pace. Last time I did an AeT test per this site, I held ~148HR for an hour, but was at around 9:10-15 pace. So perhaps I’ve gotten more fit. In Judd’s methodology, this is top of Zn2, same as Scott, et. al. Again, consistent with my experience.

    In practice, I do most long miles at around 132-135 HR. I will pick it up to 142-145 in the second half of a long run. If it’s hot out, it will drift up there on its own after a couple hours.

    Judd put my Z1 range at under 141. He calls it “slow endurance.” With pace slower than 9:22. Which I do. Again, this is consistent with my experience.

    Z2, or “long endurance” for me would be 141-148. In an ultra, I’ll never be in that range other than on a short-ish hiking climb. Pace in the 9:22 – 8:42 range. A place I don’t really go.

    Z3 would be above 151 HR and faster than 8:30. Interval stuff for me.

    On energy utilization, my fat/carb crossover point is at 148 HR; 8:42 pace. Faster than I thought. I’ll never run that hard in an ultra; that’s marathon pace. At 100 mile race-goal type paces (early flat miles slower than 11’s; averaging slower than 12-13’s with walk breaks, etc.) I am burning 65-70% fat. Only 185 – 200 carb calories an hour. This is good news for fueling strategy.

    My max fat rate of only 0.83g/min is a little low. He said it’s good for a trained runner, but could be a lot higher with specific fat adaptation strategies. But I don’t think I need to go there. That max fat burn rate comes at 9:14 pace, and I won’t be going anywhere near that fast.

    I did this mainly out of curiosity. I am happy that the results match what I’m feeling, and what they folks on this site have been saying.

  • Inactive
    Anonymous on #55179

    Judd is very good at his job!

    Treadmill running paces do not correlate well to running outside.


    AshRick on #55205

    Right…the treadmill paces were all a bit faster than what I do outside; the PE matched HR zones. I mentally adjusted!

    fharteaga on #55889

    Hi! I want to share my experience with Judd and the results (link). He is fantastic! He spent a lot of time explaining to me many stuff pre and post-test, highly recommended!

    fharteaga on #55890


    -32 years old male, 72.6kg, 183cm, outdoor enthusiast with an active lifestyle, currently living in the east bay. I never had a training plan (just “run” before significant events), but TFNA convinced me that I should. I started the 24-week training plan twice (June 2020 and Jan 2021) but dropped it in the 11th and 5th weeks. I attribute those decisions to covid and moving overseas, but probably just excuses. By then, I set the top of my zone 2 at 148bpm.

    I want to give another chance to the 24-week program. The plan averages around 7hrs of aerobic work per week, a total investment of 168 hrs! I thought it was worth paying 230usd for the gas exchange test to get a more precise estimate of the AeT and maximize the potential outcome of the training.

    fharteaga on #55892


    (Metabolic efficiency + lactate, 9am. Results in this link)

    As I want to train for mountaineering/ski touring, the test was walking.

    The last food intake was 12 hrs before the test. My warm-up was 20 min of walking on the treadmill at speed/inclination that allowed me to stay in the range of 120-135 bpm.

    fharteaga on #55894

    The test increased speed and then increased inclination (see table on this link for details). If there are only speed increases, there is a risk that the crossover happens right when you need to start running, and that may mess with the results (this is what I understood, or maybe misunderstood). Perhaps I should have done it at a constant speed, starting with no inclination

    fharteaga on #55895


    I was expecting to have a case of Aerobic Deficiency Syndrome, but I think it is not the case. I’m happy because my training is not going to be as slow as I was thinking.

    From the lactate results, my training zones are:

    Z1: ?? – 159 (initial rise)
    Z2: 159 – 175 (baseline + 1mMol: for me this is below
    Z3: 175 – 193
    Z4: 195 – 200
    Z5: 200 – 202

    From the gas exchange results, my estimated crossover point (RER=.85) is at 159bpm and FATmax at 178bpm (311 FatCal/hr).

    fharteaga on #55896

    MY PLAN:

    -Start training next week (24-week plan)
    -Try to do aerobic workouts fasted in the morning
    -Reduce carbs and increase fat on my diet. Judd recommended having a flexible diet: carbs around intense workouts/events and reducing carbs before aerobic workout days (this is very close to the recommendations on the “Train to burn fat” article).


    -Move the crossover to the right (now on 159)
    -Increase fat utilization at low intensity (now is not higher than 63%)
    -Increase output at the same heart rate level.

    fharteaga on #55897


    In case someone wants to engage 🙂

    1) My crossover happened at 159bpm while walking at 3.2mph, and 10%, similar to the last plot of the “Getting Tested Part 2” article, which represents a man with “poor fat adaptation and poor aerobic capacity.” I presume that this guy reached the crossover with a low heart rate, based on the conclusion that he had a poor aerobic capacity. I have the same output and the same ratio of energy utilization but at 159bpm. Does that mean that I don’t have ADS, but I’m in bad shape?. In that case, should training have a different physiological effect on me than on that man?

    2) When training generates increases in output at the same heart rate, does that correlate with more energy production or better energy utilization? In other words, do calories per hour increase 1:1 with increases in output at the same bpm?

    3) At my crossover (159bpm), I’m burning 280 CarbCal/hr. If the body can absorb a max of 60gr/hr (2.4 gels: 240 calories), it means I cannot replace all the carbs with gel intake. But at 149bpm, I’m burning around 220 CarbCal/hr. Would you say that the following statement is somewhat true? In an event at 149bpm or lower intensities, I could replace most of the burned carbs with the proper sugar intake and finish the event with a similar level of glycogen stores that I had at the beginning.

    4) Should I do most of my aerobic work in zone 1 (the top coincides with crossover) or zone 2 (the top coincides with FATmax)? I feel that the top of zone 1 is already high.

    5) Where would you set the top of the recovery zone (or bottom of Zone 1)? 55% of 202= 111?

    6) Any suggestion! (example: should I modify in any way the 24-week plans given the test results?)

    fharteaga on #55898

    [Disclaimer] As a non-native English speaker, I may have misunderstood some of what Judd said or what I read from TNFA. All errors are my own! And sorry about breaking the post in many, I couldn’t upload it in one.

    Reed on #55928

    Does that mean that I don’t have ADS, but I’m in bad shape?. In that case, should training have a different physiological effect on me than on that man?

    It’s more likely that focusing your training as you’ve laid out, with plenty of below-AeT work and some encouragement to prioritize fat-burning, will work great!

    One difference that I see between your charts and the ones in that “Getting Tested Part 2” article is the relatively flat fat utilization percentage for that other athlete up to a 20% grade. In his case, he was still getting ~40% of fuel from fat at a 20% grade. Your fat utilization drops off more rapidly. That makes me think of two somewhat contradictory things: you might have more low-hanging fruit and might see some rapid improvements. (This might mean looking to other areas like strength & mobility.) And you might also have reached less of your potential than that “professional mountaineer,” and therefore see continued progress for many years to come.

    On your question #2 – efficiency is a big variable. Faster speed at the same heart rate could be from better / faster energy production, and it could also be a result of improved movement economy. I’m curious how this might be quantified…

    Pay attention to what you feel. If working at the top of Zone 1 is difficult to recover from day-to-day / week-to-week, drop your target heart rate by 5bpm or 10bpm and see how that goes. For the bottom of Zone 1, I chose to set that at ~100bpm – I like getting “credit” for super easy Z1 work in my tracking. 🙂

    fharteaga on #55985

    Thanks, Reed! I will pay attention to how I feel, and I will adapt based on that.

    daniellewatsonwatson873 on #56218

    Hello, I would like to thank you for sharing this useful material. I appreciate reading it

    AshRick on #56222

    Felipe — I just got around to seeing your posts. Comparing to my test…

    First, all of my HR zones are much lower than yours. Product of age and genetics, mainly.

    My crossover fat/carb point is at 149 HR, which is also the top end of my Zn2. At the low end of that range (<141bpm), I am burning 185cal carb/hour, or less. Which is great, because I’ll do any long trek or ultra run well under 141 HR. That is easy to fuel. Judd told me I can improve on that with some fat adaptation in the final weeks before a big event. Then carb load day before and day of.

    At the top of Zn2 (approx. marathon pace), I’m burning as much as 310cal/hour. That’s tougher to stay on top of, but I’d only need to do it for <4 hours. Regular body stores plus ~200cal/hour would do it.

    As speed improves at a given HR, that speed can be a product of economy, but in a well-trained athlete it will mostly be because you’re burning energy faster. All else equal, the athlete that burns energy the fastest will run the fastest. HR can stay low with improving pace because the muscle cells and mitochondria pull more O2 out of each passing milliliter of blood. Same number of heartbeats and breaths — more power output.

    Side note on economy — I’ve been practicing a shuffle running style in anticipation of needing it late in a 100 miler (shuffling meaning…no flight phase to the running gait; think “race walking,” but without the locked knee). At first, holding pace and switching to the shuffle caused my HR to bump up a few beats, and PE to increase. That hints at losing some economy. After a few weeks of regular miles doing it, HR and PE are now the same whether I do standard running or the shuffle, at modest paces.

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