Power @ AeT Improving, but AeT HR is not

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  • #67350

    For the past 3 months I have been doing cycles of base training with a huge emphasis on steady Zone 2, approximately 12-15h / week, with a rest week every 4th week at 50% training volume.

    Part of this training involves a 90-minute Zone 2 session right at AeT, ~4 times per week. This session is almost exactly the protocol used to test AeT as prescribed by the UA blog/book/team. So, I have been collecting HR data from all of these sessions, and plotting the HR drift every session.

    Steps to calculate:
    * out of a 90-minute workout, I treat it exactly as the AeT test, with a 15 minute warm-up at a pace which generates the anticipated AeT heart rate. Then 60 minutes holding that same pace. I continue on for a final 15 minutes, but I do not use these last 15 minutes in my data analysis.
    * compute the average HR for the first half and the second half of the 60-minute portion (minutes 15-45, and 45-75).
    * compute (HRsecond-HRfirst)/HRfirst * 100% = HR Drift
    * if HR Drift is between 2.5 and 5%, then HRfirst=AeT

    * My AeT is not really moving. I have managed to nail the 2.5-5% HR drift in the majority of my sessions (occasionally below, occasionally above). However the actual Aerobic Threshold Heart Rate is pretty much constant over the last 90 days (based on 28 test sessions of data over those 90 days). I was expecting to be able to hold a higher heart rate at a <5% drift over time.
    * I HAVE progressed – I am generating about 10% more watts at the same AeT heart rate, which is great. I’m not complaining.

    I just expected the AeT heartrate itself to shift up, rather than more power at the same HR. I thought the idea was to push your AeT closer to your AnT. My AnT is tested at 179bpm, possibly a bit higher, while my AeT is coming in at 140-144 depending on the day, with a Max HR (observed) of 201. So there should be plenty of room to push it higher.

    Is this an adaptation that comes later? Would I expect to see power gains first, before the AeT starts to increase?

    Regardless, I feel like this training is paying dividends already so I’m going to continue on and report back in another 3 months. Interested in others experiences.

    Attached is the data. I am plotting my power:HR ratio which took a couple cycles to stabilize and then began to increase. My HR drift on every given day is shown and usually within the 2.5-5% range, a few days I went out too fast and a few days I had to slow down which is why it shows negative drift. On the days when I got a valid 2.5-5% HR drift number, I calculated that AeT HR and plotted it, and am not really noticing a positive trend.

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    Shashi on #67354

    If you don’t mind, can you please make your AeT test public and share the training peaks link here? One from the start of the training and one recent?

    Here is a forum topic that discusses the timeline on improvement in AeT –

    Fixing Aerobic Deficiency general timeline? tips?

    smarshall54 on #67356

    Hi Shashi, I do not have a training peaks link, I am doing the data analysis myself. If your suspicion is that I am not doing the calculation correctly, I am pretty sure that I am. I am performing these tests on a rowing ergometer with a heart-rate chest strap, which records HR and power data every 1 second. I am very familiar with the technique and am able to keep a very consistent heartrate and power output over the full 90m period after warm-up.

    Attached are HR and Power plots for two 90m workouts 2 months apart. Both exhibit approximately 3.8% HR drift and coincidentally, almost the same average heart rate of 143 (for the middle 60 minute “test segment”) – but the average power is 10W higher in the later test.

    I can upload CSVs if you really want, but I have to do them 1 at a time and didn’t really expect anyone to dive into the data for me 🙂

    Thank you for the link, I have read that thread and it’s getting at a slightly different issue. I am already seeing gains, just not in the way I expected! I was hoping that my data could help out others and that maybe someone else had experience with periodic testing and whether they saw AeT-HR improve first or power@AeT without shifting the actual AeT like I am seeing.

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    bill on #67435

    I had a conversation about this with Mark Postle during one of our mountaineering training zoom calls. Of course the answer is, it depends, but… the discussion suggested that most of the aerobic improvement will show up in speed and power without moving AeT a lot unless you are really unfit when you start. If you are doing 12 to 15 hours of Z2 work, you aren’t in that category.

    Part of this seems to be related to AnT; it is just hard to get the difference between AeT and AnT to less than ten percent unless you are training at an elite level. And once it is less than ten percent, it is almost impossible to move. Part of it may also be related to age. My AeT is limited by age, as my maximum heart rate decreases, so has my AnT and AeT. If you are already pretty fit, raising your AeT is going to be hard, even if improving your power and AeT endurance is not.

    But, after all, if your speed and power continue to improve, whatever your AeT might be, does it really matter? Your endurance is improving, you are getting faster, you are getting stronger, which is really the point of all this.


    smarshall54 on #67453

    Hi Bill, thanks for the information. I am very happy with the progress I have observed so far, just trying to square my understanding with what the book suggests, which is moving the AeT.

    I’m 34 and definitely not elite fitness, or even that competitive, I just have time to train right now.

    My confusion is that my AnT is 179 and AeT is 144, a difference of 25%, even if I can’t get to 10% I figured it would be at least a little trainable.

    Anyway, I could be jumping the gun here. I understand the HR drift test and AnT test protocols are not an exact science, and that the “10% rule” is just a rule of thumb. And it has only been 3 months, and the AeT measurement is noisy due to recovery status.

    I’m going to carry on and see what things look like in another few months. I’ll post more data when I do. I appreciate the responses!

    bill on #67514

    Good morning! I am wondering about your max heart rate because 179 seems on the high end for AnT. How did you determine your AnT? As a rough estimate, using Heart Rate Reserve (Max HR – Resting HR), you can calculate AeT at HRRx0.75 + RHR and AnT at HRRx0.85 + RHR. As an example, my tested AeT and AnT are pretty close to these calculated estimates.

    Another observation… are recovery weeks at 50% of your current training volume really letting you recover? How do you actually feel during recovery?

    As another data point, I was fairly aerobically fit when I started the UA training programs but still met the definition for ADS. I started seeing speed and endurance improvements pretty quickly but my AeT didn’t move much for the first four or five months. It has gone up a bit since them but given my age and current max heart rate, it probably isn’t going to go up much more.

    Good luck with your training!


    nickdhulster on #67799

    That calculation is wild! I just plugged in the numbers and it’s almost identical to what I was seeing last season before this style of training. It’s changed for the better over a couple cycles. It’s almost like a MAF number but more personalized. Thanks for the info.

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