Hi Steve I think we are sort of talking about different things and have deviated off topic. My concern is using DFA a1 as a measure of HR breakpoints for At or AeT. Tough it may well be quite valid to do so, my question/ comment relates to the fact they are both response variables. However, when I take a step back I might see DFA a1 as a response to over all individual chronic stress, whereas HR is a slightly delayed response to acute stress. For running this might be the only real time relationship one can work with unless one has a running power meter.
To summarize, my concern is I see DFA a1 vs HR as 2 response variable correlation (your HR is not the stressor something else is), whereas DFA a1 to power is a response vs input stressor relationship. Though in the latter case power is not the only stressor, core temperature, nutrition (ie. caffeine) and other things can impact the response. So I still think to get to some kind of metric for determination of At or Aet it is still a messy game and a really fascinating topic.
Hi Steve, @chris, @trevor I looked back through the podcasts and don’t see where in the last year or so that you have had a podcast discussing DFA a1? I see in July 2020 you had one n setting thresholds and maybe that needs to be revisited with maybe some input from Bruce Rogers, Marco Altini, the guys from Runalayze, etc? I would tune in for sure. Particularly the way you guys dig into the details.
Yes we have sort of deviated…I was just recommending, if you are using the app (which I have) that you might experiment with a hr step test, just might be interesting what you might see.
I am having a client do a heart rate step test, and a normal power-based step test, with HRV and Moxy monitor on, will share with you once done.
I rode at a constant heart rate for the times stated below. I did not attempt to control power. Why did I start at 135bpm? I have always used 136bpm as my LT1 cutoff, so I wanted to see how DFA 1 alpha responded. DFA 1 alpha never got close to 0.75, so I increased my heart rate to 141 for the next 10 minutes. I still didn’t cross 0.75 and stepped up my heart rate to 146. After riding at 146 bpm for 10 minutes, DFA 1 alpha crossed 0.75 for the first time. I continued for another 2 minutes to get confirmation and got another reading below 0.75.
Steps:
0-10 min warmup
10-50 min: 135bpm (74% of max) and 200w. 3.2% Pw:Hr (cardiac drift per Training Peaks)
50-60 min: 141bpm (77% of max) and 205w. -1.3% Pw:Hr
60-72 min: 146bpm (80% of max) and 211w. 0.5% Pw:Hr
Z2 cutoff from other sources (5 zone model):
Oct 2021 Aerotune Powertest = 200w.
Jul 2019 INSCYD test = 205w.
WKO5 iLevels = 216w.
WKO5 classic power zones = 208w.
Other data points:
WKO5 model FTP = 284w
Oct 2021 Aerotune Powertest Critical Power = 281w
Learnings/thoughts:
My LT1 cutoff heart rate is possibly a bit higher than the 136 bpm I have used for a few years. Maybe 141?
DFA 1 alpha doesn’t seem to instantaneously respond to increased effort. Maybe it’s like a lactate test, where you have to ride at a certain effort for a while before taking the lactate reading?
I rarely ride right on top of the LT1 cutoff. Recent endurance rides have varied from 117bpm/157w for four hours to 130bpm/189w for 2:30.
Thoughts and observations are very welcome. What am I missing or misinterpreting?
Using the HRV4 training app only gives you a reading every 2 minutes which would/could account for a lot of the delay. Using the Android App Fatmaxxer gives you a reading every 5 secs and do should be more responsive. I too have found that long intervals seem to give a much better idea of where LT1 is. Ramp tests give me a much higher readings than I think are correct.
I’ve used both those apps and they have given the exact same point for crossing 0.75 in terms of HR. The protocols all suggest long steps in any ramp test so its clear it takes time to respond, just like lactate tests. FYI, its well into my z3 heart and power zones which surprised me as I expected it to fall in z2. I’ve since heard the same from quite a few other people.
I haven’t, and wont, do any lab tests for confirmation and will use this as a guide for a LT1 ceiling and perhaps some fatmax work in future. When I’m stuck indoors on the trainer and its not a day for any kind of intensity, I think its a handy guide to understand where I might target some 90 min tempo rides for max impact.
Today I did a slightly different protocol with this. I did a 15 minute warm up to the steady state heart rate I wanted to try. I then did 30 mins as steady state as I could. I intended to look at Fatmaxxer DFA1 in real time whilst cycling in turbo but phone turned screen off and it was out of reach.
A heart rate of around 130 bpm was too high for a DFA1 of 0.75. The graph looks like wide range but it’s only 6 bpm difference. I came up averaging around 0.6 for DFA1. I’m going to repeat the process tomorrow morning with a target steady state of 125 bpm. I’ll also change my phone so the screen doesn’t turn off and I can see it in real time.
I know it was around 135 - 137 bpm a year back. Looks like some long easy rides are in order to raise LT1 again.
start at 50% max heart rate, this will be very low wattage, don’t worry about it.
then increase 5% every step.
Try and keep the heart rate plus or minus 1% of the goal heart rate.
Try and keep the cadence as steady as possible between 80-90 if possible, but worry more about the heart rate than the cadence.
Once you are done please share the fit file with me.
Find me as a coach on intervals.icu as well.
hit the lap button at the beginning and end of each step, yes your power will jump a bit as you try to increase wattage, but it will settle and all work out.
I assume this is done like a typical power step test. Continue with the 4m steps until we can no longer maintain the required heart rate within 1%. Once complete, does this give us an estimate for Aerobic Threshold and Lactate Threshold?
actually it is not exactly a typical step test. The references above from Bruce Rogers suggest that you go to exhaustion though I see no reason it will not work as long as the ramp rate is in the right range. There is still work to be done to confirm the second break point of DFA a1 at 0.5 though there is reason to believe this is the second threshold.
The basic answer is:“Just perform a typical ramp of 5 or 10 watts per minute”. I have tried both a stepped approach as well as a smooth (unstepped) ramp and the results are very similar. Yes you want to use erg mode in my opinion. You do not go to exhaustion for the AT1 that is your lower threshold and should be where you are riding “easy”. The point is for you to know where the boundary is for those easy rides. This break occurs at a DFA a1 of 0.75. The second break point is the boundary between aerobic and anaerobic threshold at a DFA a1 of 0.5.
For anyone coming across this aerobic threshold detection method (Alpha DFA 1). I just went through the process using HRV Logger and then came across a new blog post dated 14/3/22 by Marco Altini in which he concludes:
‘The universal threshold of 0.75 does not identify the aerobic threshold with reasonable accuracy at the individual level’.
It’s worth checking out the full article for more details. Hope this helps.
I don’t think it is useless, but it is something like the 220- age HR max… it is not universal, but at the general level it works OKish… so though for me the 0.75 limit may not work then again neither does the 220- age for HR max. I think at the root it has some utility but at the individual level may need some further study and refinement. I agree with Marco’s point they should have removed outliers from the data, there are statistical methods to do so which may have made the process show what Marco is noting that once the extreme values are removed the correlation is poor. If you use HRV Logger one short coming there is unless you check the data in another program the 2 minute reading to reading output is not good for the purpose, however it does record the data and if run in another program then you can see much finer detail. The otehr thing with DFA a1 is that it is determined by previous research that a 2 minute window is best, which means that the data is heavily smoothed, ie if your heart rate is 140 bpm, then you have 240 data points that are used to calculate the DFA a1. That as well may impact how the method reacts to changes, ie it needs to be a fairly significant change to move the result, though the math is way over my head for calculating DFA a1. So this is a neat new thing but it may be a while before we know if it works and how best to utilize it.
