Surprisingly low aerobic threshold (drift test)

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  • #36696
    agk38
    Participant

    Hi all, I recently tried 4 iterations of the heart rate drift test described here. From my understanding, when the decoupling/drift is less than 5%, you should take the average first half heart rate and set that as your AeT (top of zone 2). I am a 25 year old male, so as a very general starting point, I would assume my AeT should be somewhere around 137 bpm (70% of the old “220 minus age” rule of thumb). However, my tests are showing closer to 108 which seems like a huge discrepancy.

    Below I’ll describe the tests in detail (spreadsheet with full data is also attached). I would be grateful if anyone could point out something I’ve missed, or perhaps my AeT really is that low?? This is my first serious attempt at training for mountain endurance events, but I have been an athlete in other regards all my life. Currently, I’m 6’2″, 195 lbs, and 6.4% body fat (measured by InBody scan at the gym), so I’d like to think I’m in good shape, but this AeT result seems rather poor

    All tests conducted on a stair stepper with a Polar H10 chest strap to measure heart rate. I did stairs continuously at the same pace/difficulty level for 70 minutes (10 minute warm-up and then two 30 minute halves). Results are below, formatted “stair stepper level: first half HR / second half HR = decoupling percent”. If it’s relevant, I did these tests in Denver (5,410 ft. elevation)

    7: 138.7 / 151.0 = 8.9%
    6: 120.8 / 129.4 = 7.1%
    5: 117.2 / 124.5 = 6.2%
    4: 108.6 / 114.9 = 5.9%

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    Reed on #36705

    In my first experience following a structured endurance-focused training plan, my anaerobic threshold (AnT) heart rate increased by 20bpm over a 3-month period. My aerobic threshold (Aet) heart rate at the end of that training block was equal to my AnT heart rate at the beginning. My years of intermittent running & powerlifting did not translate into a high AeT.

    It sounds like you’ve been methodical about dialing in your AeT. You could consider getting a second opinion via a lactate test (I believe many people on this forum have gone to the lab at CU Boulder). Or base your training on these results, and spend a few months training below 110bpm, and re-test.

    The age-based heart rate ratios apply to populations but with huge individual variance – best to ignore those.

    Keymaster
    Scott Semple on #36723

    I would assume my AeT should be somewhere around 137 bpm (70% of the old “220 minus age” rule of thumb). However, my tests are showing closer to 108 which seems like a huge discrepancy.

    A discrepancy with what? Generic formulas describe populations, not individuals. Throw them out the window.

    A lower than average heart rate for anything doesn’t mean anything other than it’s lower than the average (not in terms of quality or ability, just in terms of the number of beats per minute.) The reasons could be ADS or it could be quite normal. Perhaps your heart is larger relative to your size, so it doesn’t have to pump as frequently. Who knows? You need to compare it to something meaningful to mean something.

    Currently, I’m 6’2?, 195 lbs, and 6.4% body fat (measured by InBody scan at the gym), so I’d like to think I’m in good shape…

    This only tells you that you’re lean. To know if you’re in good shape, you need a comparison to a performance benchmark.

    …but this AeT result seems rather poor

    Heart rates are like fingerprints. In isolation, the number doesn’t mean anything. As above, you need to compare it to something to guess at the meaning.

    first half HR / second half HR

    Is that a typo maybe? For a drift test, you need to reverse that. You need to divide the second half by the first.

    In addition to what Reed said, you could do an anaerobic threshold test. That’ll give the AeT number some meaning because you’ll have something to compare it to.

    And again! Higher is not better with heart rates. So if your AnT HR is “low”, don’t worry about it. The relationship between the two and how they change is what’s important. (To start with anyway. Then speed is what’s really important.)

    Participant
    agk38 on #36743

    Thanks for the quick replies Reed and Scott! On the age-based population formula, I know individuals will have very different results. Nearly 30 bpm difference seemed like more variance than I would expect in the population, so I wanted to make sure I was conducting and interpreting my AeT tests correctly

    To clarify the “first half HR / second half HR” typo, I used the “/” character as a delimiter, not literal division. Bad ambiguity on my part, but the decoupling percentages are still written accurately following the second half divided by first half formula

    I might consider the lactate test as confirmation depending on the price, but it sounds like I can get some good improvements going off the drift test alone as well

    Correct me if I’m wrong, but I thought one of the main goals of an endurance-focused plan is to increase your AeT? That way, the difference between your resting HR and AeT increases which gives you a bigger cushion to do harder activities while remaining in your aerobic zone. For instance, hike/run faster on an approach while staying in the aerobic zone (which is more efficient since you primarily burn fats for energy vs. carbs)

    The AnT test sounds interesting – I have the Mountain Guide Manual book and hadn’t heard it mentioned in there. From the link, it sounds like the difference between AnT and max HR is just the amount of time you can sustain it for? Max HR is a few seconds, but for AnT you should be sustaining the “maximal effort” for 30-60 minutes

    Participant
    Shashi on #36753

    agk38,

    Just curious, why did you decide to do only 10 min. warm-up? Is it because your heart rate reached the desired level and was stable at around 10 mins?

    I see that all your tests are done on Stair Stepper at different difficulty levels. Have you tried doing the heart rate drift test on a treadmill? I am not sure if it matters, but just a thought.

    Keymaster
    Scott Semple on #36775

    Correct me if I’m wrong, but I thought one of the main goals of an endurance-focused plan is to increase your AeT? That way, the difference between your resting HR and AeT increases which gives you a bigger cushion to do harder activities while remaining in your aerobic zone. For instance, hike/run faster on an approach while staying in the aerobic zone (which is more efficient since you primarily burn fats for energy vs. carbs)

    Yes. The first, least-informative adaptation is heart rate. Threshold heart rates (for both AeT and AnT) will rise and converge.

    But what really matters is speed. While the HR changes may happen in a matter of months, threshold speeds can improve for years (while heart rates don’t change).

    …it sounds like the difference between AnT and max HR is just the amount of time you can sustain it for? Max HR is a few seconds, but for AnT you should be sustaining the “maximal effort” for 30-60 minutes

    Not exactly. “Maximum” is always duration-dependent. For example, the maximum speed that you can maintain for five seconds is a lot faster than the maximum speed that you can maintain for 60 minutes.

    With threshold tests, you’re not trying to maintain a heart rate. You’re maintaining the highest sustainable speed–or, less perfect, an effort level if speed can’t be measured–that you can for a given duration. Then after the test, you can find out what your average heart rate was. During the test, there’s no need to even look at your watch to find out.

    Does that make sense?

    Whenever a prescription is “as hard as you can for X minutes”, it does not mean that you should go out at a full sprint and hang on for dear life until the bitter end. In that mistaken case, your average speed will be far lower than what it could have been with a more measured approach. (The For Dear Life method is also affectionately known as the strong-like-bull-smart-like-tractor approach.)

    In contrast, maximum heart rate is the fastest rate that your heart can beat regardless of the intensity level. I assume that it is limited by things like genetics, its size, etc. Most importantly, maximum heart rate is not a workout intensity while AeT HR and AnT HR are.

    For example, if your AeT HR right now is indicative of lower than average heart rates. in general, then perhaps your maximum is under 160. On the other end of the spectrum are max HRs of over 200. Neither is a measure of fitness, it’s just a way to quantify how fast the pump can pump.

    Participant
    agk38 on #36787

    Shashi

    Just curious, why did you decide to do only 10 min. warm-up? Is it because your heart rate reached the desired level and was stable at around 10 mins?

    That’s just what the Training for the New Alpinism book recommends. After 10 minutes, my HR had stopped changing from the initial warmup and was steady for the intensity, which is where you want it to be

    I see that all your tests are done on Stair Stepper at different difficulty levels. Have you tried doing the heart rate drift test on a treadmill? I am not sure if it matters, but just a thought.

    I thought stair stepper would be a bit more applicable to step hiking, but like Scott says you’re just trying to maintain a constant speed in a threshold test, so I think any machine that can set a fixed speed should work

    Scott

    With threshold tests, you’re not trying to maintain a heart rate. You’re maintaining the highest sustainable speed… Does that make sense?

    Yes I’m following you there. I don’t pay attention to my watch during the AeT tests, just crunch the numbers afterwards. For AnT, the perfect speed would be where you never need to slow down but are still exhausted after the 30 minutes?

    When you say “threshold speeds”, you mean the pace (i.e. mph, steps/min, etc.) that you can produce at your threshold HR? Can those speeds really improve without the threshold HR also increasing? It seems like for your body to output more power (higher pace/speed), you need more oxygen supplied to your muscles = higher required HR. Unless your muscles become more efficient at using the fixed amount of oxygen they receive… perhaps that’s the key point I’m missing

    Keymaster
    Scott Semple on #36807

    For AnT, the perfect speed would be where you never need to slow down but are still exhausted after the 30 minutes?

    Yes, exactly. In reality, you’ll have to ramp up to it to get the best result.

    When you say “threshold speeds”, you mean the pace (i.e. mph, steps/min, etc.) that you can produce at your threshold HR?

    Yes.

    Can those speeds really improve without the threshold HR also increasing?

    Ohhhh, yes. With a lot of the right training, the speeds can increase a lot.

    It seems like for your body to output more power (higher pace/speed), you need more oxygen supplied to your muscles = higher required HR. Unless your muscles become more efficient at using the fixed amount of oxygen they receive… perhaps that’s the key point I’m missing.

    Yes, you answered your own question. This is why training below Zone 2 is so important. You need to increase the mitochondrial mass in your muscles. The more mitochondria, the more fat, oxygen, and lactate you can process.

    Participant
    agk38 on #36811

    Really excellent blog post in your link Scott. Neat to see the long-term changes in your threshold HRs and paces. I jumped over to another article of yours “Aerobic Capacity: When can I stop?” and was wondering about the 10% rule between AeT and AnT since it’s also mentioned on The Uphill Athlete page for the AnT test. Taking my AeT as 108 from tests so far, I would have the following zones

    1: ?* – 97**
    2: 97 – 108
    3: 108 – AnT
    4: AnT – not really relevant***
    5: not really relevant

    * How should I determine the lower end of zone 1 – another 10% off the AeT?
    ** I get 97 as the top of zone 1 from The Uphill Athlete page for AeT drift test which says subtract 10% from the AeT
    *** Since we’re talking endurance training, I don’t think I need to be concerned about these

    I haven’t done the AnT test yet, but I can pretty much guarantee it will be higher than 120 (which is the 10% cutoff). Given that, The Uphill Athlete recommendation is to “do all of my aerobic base training in zone 2”. Then, as the AnT/AeT gap becomes less than 10%, I should reduce the amount of zone 2 and move towards primarily zone 1 for my base training. In your blog post, you recommend “add[ing] a small amount of high-intensity training” once the thresholds are within 10% – so would that be small amounts of zone 3 with zone 1 still being the primary percentage of your training time?

    Like you say in the post, it definitely requires a lot of mentally discipline to not train above the AeT in order to build a base!

    Keymaster
    Scott Semple on #36829

    Taking my AeT as 108 from tests so far…

    I usually err on the conservative side and round down to the nearest five. It’s also easier math to calculate other zones and remember them if they have a base of 5.

    It also false precision to define a threshold, which is very dynamic, as “161” or “123”. SO I would use 105 as AeT. There’s no downside.

    * How should I determine the lower end of zone 1 – another 10% off the AeT?

    It’s pretty fudgy, but I usually use 50% of AeT. It’s not really that important though. Anyone who’s training seriously is already motivated to maximize performance, so as soon as the running shoes are on, they’re going to take it right to the line. The upper limit is more important in order to hold us back.

    ** I get 97 as the top of zone 1 from The Uphill Athlete page for AeT drift test which says subtract 10% from the AeT

    Yeah, 10% is the rule of thumb that we use, but in your case I would use 90. ~10 beats is not much of a window. Also, if your new to aerobic training, defining is Z1 is less of an issue. Eventually, with enough multi-year volume, Z2 will become quite fatiguing. That’s when defining Z1 becomes more important.

    *** Since we’re talking endurance training, I don’t think I need to be concerned about these

    I think it’s worth doing an AnT test though. Because your AeT BPM is lower than average (again, just as a number, not as a performance indicator), it would be good to know how much of a spread you have between AeT HR and AnT HR.

    …so would that be small amounts of zone 3 with zone 1 still being the primary percentage of your training time?

    It depends on the goal event, but yes, Z3 is the most common intensity at that point.

    It’s also worth noting that most people don’t have to worry about that for quite some time. For example, my HR thresholds have been very close for 15 years, largely because of lucky circumstance of a lot of long alpine climbing days from 1999 to 2005. But even after I started structured endurance training in 2014, it took me three years before AeT was too fatiguing for continuous training.

    Like you say in the post, it definitely requires a lot of mentally discipline to not train above the AeT in order to build a base!

    Yes, but then it can become like meditation. I think of it as “my grocery list pace”. When I’m in Z1 now (which is most of my training), the last thing I think about is intensity. I don’t listen to music or podcasts, so I just zone out, usually thinking about blog posts I want to write.

    Participant
    agk38 on #39818

    Hey Scott, checking back in after completing the max strength portion of my base period. I followed the recommended training modes for an 8-week mountaineering plan (found on pg. 247 of Training for the New Alpinism). After confirming my AnT as 160 bpm, I kept all of my aerobic training in zones 1 and 2 (85-105 bpm). You can see the recorded weekly volume in the attached screenshot. Note that the “zone 1” column is really zones 1 and 2 combined since my AnT-AeT gap is more than 10%. I did not actively try to do zone 3 workouts, those were just the minutes that accumulated as a result of me temporarily going too fast during a zone 1-2 workout.

    Now I am starting the muscular endurance period of my base training (planning for 12 weeks). The main recommendation from the book is to do water jug carries up a steep hill, so I tried my first one today. In order to keep my HR below my AeT, I had to go painstakingly slow. Completing 0.37 miles with 500 ft. of elevation gain took 32 minutes and required multiple complete pauses in order to keep my HR low enough. Based on the book’s recommendation to gradually increase weight over the course of 12 weeks, I started with only 10 L (22 lbs, ~10% bodyweight). I’ve hiked before with 20 L and I’m confident I could do 30+ L as well.

    The problem is, even with a ton of extra weight I feel that my breathing and AeT are still going to be the limiting factor for speed, which is the opposite of what the book recommends – “if you are able to hike fast enough to get short of breath, you need to add more weight or pick a steeper hill”. At some point, more weight seeems to turn this into a strength workout rather than an endurance one. I also think the hill is pretty steep grade, and it happens to be close to my house with a source of water at the base. Do you think I will see improvement in my AeT pace if I continue hiking at such a slow pace, or should I consider an alternative workout for my muscular endurance base?

    Thanks for the input!

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    Reed on #39827

    Nice job consistently adding more time in Z1 / Z2. You might consider deferring muscular endurance workouts until you’ve ramped up your aerobic volume further, and substantially narrowed the gap between aerobic & anaerobic thresholds. If you’re trying to close the gap between a 105bpm AeT and a 160bpm AnT, think about giving your body time to build new, denser capillary networks, strengthen tendons & bones, etc. – structural changes that will take months to start seeing and can continue for years.

    I’ve found that 30-45 minute easy aerobic runs four days per week (Tue/Wed/Fri/Sun), 90-120 minute long run (Sat), and some strength / core (Mon/Thur) to be a workable schedule for me. Low volume relative to most of the athletes here. But this has led to pretty good improvements over the past couple of years.

    Keymaster
    Scott Semple on #39854

    Reed’s suggestion is a good one. Especially with many trips and objectives being cancelled, inaccessible (because of park closures), or inadvisable (because of the reduced capacity of the health care system), this is a great time to focus on improving fundamentals. That will serve you much better in the long run.

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