Saturday, January 2, 2021

DFA a1 and exercise intensity FAQ

With the recent interest in using the DFA a1 HRV index to determine aerobic thresholds, to follow exercise intensity (Runalyze and AIEndurance) and the use of real time DFA a1 output from alpha HRV for Garmin and Fatmaxxer, I've decided to put together a "frequently asked questions" list.  This is by no means totally inclusive and will be updated on a regular basis as new questions (and answers) come up. For the most up to date published "FAQ" please see our new Frontiers article.

What is DFA a1?

  • Simply put, it's an index of heart rate, beat to beat, fractal related self similarity.  Although your heart rate may be 60 bpm, the beats are not occurring exactly every 1.000 seconds.  The pattern of self similarity changes as exercise intensity rises, from values well above 1, moving down to .75 near the aerobic threshold and dropping even further above this exercise intensity.  See the articles below for details.
  • Uses of a1 observation include first and second ventilatory/lactate threshold estimation as well as monitoring for fatigue effects.

This is an illustrative figure of DFA a1 behavior over exercise intensities of 3 very different individuals (based on prior study participants) from our latest review:

A: DFA a1 vs HR of a 26-year-old male runner with a VO2max of 72 ml/kg/min, HR at VT1 of 183 bpm and HR of 192 bpm at VT2 performing an incremental treadmill ramp test. Shading indicates a 3 zone exercise intensity model defined by DFA a1 thresholds. 

B: DFA a1 vs HR of three participants during incremental exercise ramps. 

  • Red circle: 59-year-old male with stable coronary artery disease (CAD), beta blocker usage and a VO2max of 25 ml/kg/min, HR at VT1 of 83 bpm and HR at VT2 of 109 bpm performing an incremental cycling ramp test. 
  • Blue circle: 23-year-old female triathlete with a VO2max of 60 ml/kg/min, HR at LT1 of 154 bpm and HR at LT2 of 165 bpm performing an incremental cycling stage test. 
  • Green circle: 19-year-old male runner with a VO2max of 58 ml/kg/min, HR at VT1 of 167 bpm and HR at VT2 of 179 bpm performing an incremental treadmill ramp test.

 Background:

  • Here is an earlier Podcast I did with Michael Liberzon of x3training.com

Can it be used to determine the aerobic threshold and other aspects of exercise intensity?

  • Below is a YouTube video I did for a conference going over the advantages of DFA a1 over other indexes
 
 
 

How accurate is it for threshold identification?

  • Before answering, we need to think about how accurate the comparison "gold standards" methods are.  As discussed in the articles above, there are real issues in both lactate and gas exchange tests, making them subject to various errors and inconsistencies.  Some gas exchange results are so confusing that they are not interpretable.  Machine based gas exchange results are not always accurate.  From the limited study data so far, it seems the DFA a1 is a reasonable surrogate for the AT.  Below is the Bland Altman analysis and regression plot from our validation study:


 
  • As you can see, some folks had more or less agreement with the gas exchange AT, but for the most part the differences were small (several bpm)

What sports can this be applied to?

  • This is a good question.  So far, only running and cycling have been well explored.  Other activities such as those using upper and lower extremities (xc skiing, kayaking, rowing) may not follow the same relationship with the AT. 

What can affect the numbers I get?

  • A very wide range of factors.  Stress, heat, caffeine, caffeine withdrawal, food, fasting and over-training are some of the factors before we even process the data.  Preprocessing algorithms, software settings are also critical.  Kubios may give different results from a python based method. We will need to do formal comparison testing between Kubios and python methods eventually.
  • Should I use a fan indoors - YES -
    Another look at indoor exercise without a fan 

Do I need clean, artifact free data?

  • A very important item that will affect the DFA a1 is artifact in the RR series.  Missed beat artifact is the most common, and if above 3% could, but if above 6% will affect the values you get.  A single APC may also dramatically drop the DFA a1 for that window of measurement.  Correction methods help with this but are not perfect.  One of the strengths of our Frontiers study was that we used ECG data with almost no artifact.  YMMV using a chest belt with artifact.
  • We recently had an article published in the journal "Sensors".  Below is the abstract from that study:
 
Recent study points to the value of a non-linear heart rate variability (HRV) biomarker using detrended fluctuation analysis (DFA a1) for aerobic threshold determination (HRVT). Significance of recording artefact, correction methods and device bias on DFA a1 during exercise and HRVT is unclear. Gas exchange and HRV data were obtained from 17 participants during an incremental treadmill run using both ECG and Polar H7 as recording devices. First, artefacts were randomly placed in the ECG time series to equal 1, 3 and 6% missed beats with correction by Kubios software’s automatic and medium threshold method. Based on linear regression, Bland Altman analysis and Wilcoxon paired testing, there was bias present with increasing artefact quantity. Regardless of artefact correction method, 1 to 3% missed beat artefact introduced small but discernible bias in raw DFA a1 measurements. At 6% artefact using medium correction, proportional bias was found (maximum 19%). Despite this bias, the mean HRVT determination was within 1 bpm across all artefact levels and correction modalities. Second, the HRVT ascertained from synchronous ECG vs. Polar H7 recordings did show an average bias of minus 4 bpm. Polar H7 results suggest that device related bias is possible but in the reverse direction as artefact related bias.

 

So what does this mean on a practical basis?  Anything with >6% artifact in the area of interest should not be trusted.  Since both the Kubios threshold correction method, Runalyze, Fatmaxxer and HRV logger use similar techniques, 3% or less artifact containing data will provide reasonable HRVT accuracy.  There is also a chance that 3-5% artifact containing data series will be fine, but you may want to re test yourself.  The effect of missed beat artifact on DFA a1 is to artificially raise the computed value at low DFA a1 ranges (not high ranges).  For example, if the DFA a1 was .5 with no artifact, after adding 6% missed beats with correction (by Kubios), the software will output .65 +-.  

Here is a look at how that works out on a Bland Altman assessment


The solid line is the "average" difference between methods, notice how this process is dependent on what DFA a1 actually is.  There is minimal "bias" between DFA a1 of 1 and .5 which is important for the HRVT.  However, values below .5 are very much altered.

  • Also see below under recording devices.
  • It appears the greatest source of missed beat artifact is the use of AnT+ data transmission.

What artifact correction settings do you recommend?

  • If you are using the Kubios paid premium version, use the "auto" method.  Free version Kubios uses the threshold method (similar to HRV logger, alpha HRV, Fatmaxxer and Runalyze).  The medium correction setting is the default and should work well (similar to the 20% setting in FM, Runalyze and Logger).  The exception is with an APC where a sudden drop is seen.  Using the extra strong filter setting (or the "work out mode" in Logger, 5% or auto in Fatmaxxer) will filter out the APC but can also filter some physiologic beat to beat variation.  Get a feel if you exhibit frequent APC activity, and if so, use the more aggressive settings.  IMO, Fatmaxxer has the best method - automatic alteration of threshold mode as HR rises.

Does recording device matter?

  • This is something else we are looking at.  The above validation study was done with a research grade ECG.  It is very possible that a chest belt device will detect R peaks differently as well as be affected by preprocessing issues.  Interference with either chest wall or diaphragm related activity can change the ECG waveform.  Disturbance of the pattern of self similarity would then occur after the introduction of this type of distortion.  However, the Polar H10 results appear very close to accurate waveform ECG derived values.
  • Also see this: DFA a1, Sample rates and Device quirks 
  • In the Sensors study, we found that the Polar H7 "measures" DFA a1 as slightly lower values.  This is in the opposite direction as what missed beat correction induces, which is actually quite convenient!  The end result of a Polar H7 recording with 3-5% missed beat correction may yield values that are very close to those of an ECG.  Below is a figure from our article that shows this very nicely.  The Polar reads lower than the ECG, but the 6% artifact recording reads high - making for a "self correcting" effect.  If you had a Polar RR series with no artifact, yes, you might have bias.  We are continuing to look into this.

    Time-varying analysis (window width: 120s, grid interval: 5s), DFA a1 for matched time series containing no artefact in one representative participant, ECG (solid triangle), Polar H7 (open circle), ECG 6% MC (open triangle).

     

I have the option of recording HRV either using ANT+ or bluetooth - is there a difference?

YES and No

  • Although I initially couldn't believe this should make a difference, it apparently does!  Here is an experiment I ran.  The first tracing shows a recording using a Polar H10 to my Garmin watch using Ant+.  The second is a recording of the same power/duration/conditions on another day using bluetooth (same H10, same watch).


  • There are clear differences - the bluetooth tracing has zero missed beats (one APC noted), but the ANT+ recording has many (the vertical lines).  This has been replicated many times and is reproducable.  
  • Bottom line - if you are seeing many artifacts using ANT+, try switching to bluetooth.
  • However, the new alphaHRV app for Garmin devices uses it's own Ant+ protocol and is not subject to direct Garmin watch limitations. Garmin apparently uses a lower sample rate firmware for Ant+ to save battery which is the issue with accurate RR at high HR.

If I shouldn't use ANT+ then how can I get the RR data to both my Garmin watch/head-unit and Fatmaxxer during an exercise session?

  • The Polar H10 has a nice feature that enables two different devices to simultaneously receive RR packets over bluetooth.  It is not enabled by default so you will need to do so.  The instructions are here.
  • Once enabled you can have your Garmin watch and the appropriate app (or other bluetooth device) receive data at the same time.  But remember, other nearby receivers may be able to pick up your data and see your stats. This applies to ANT+ as well.  Using the Polar Beats app, you can turn off multi device bluetooth and/or ANT+ at will. 
  • If the H10 is already added as an Ant device in the Garmin unit we need to get rid of it - first - delete the Ant device from "Sensors", Go to - add new external HR, but don't add the Ant, the Garmin will then ask to search bluetooth, say yes and add the bluetooth HRM.
  • Note - on H10 battery change (or pull) these settings will be lost!  You will need to reapply with the Polar app.

I don't want to deal with Kubios, is there a low cost, easy option for DFA a1 tracking?


 
  • Runalyze/AIendurance are able to automatically transfer your Garmin fit file recording and display DFA a1 over time and also compare it to HR and powerThey will automatically calculate a aerobic threshold as well.  See this post for further details - Best practices for Runalyze and DFA a1 thresholds  
  • Fatmaxxer, is an app designed as a dedicated DFA a1 monitoring tool for android.  This is my choice as the option for real time a1 tracking.  Reasons include the ability to track DFA a1 at an every 5 second refresh rate and ECG strip recording of artifacts.  What does this mean?  We can get a fine/granular plot of DFA a1 over time with points every 5 seconds.  If an artifact is detected, a separate file is saved with that data to graph and inspect.  It also seems to have the best a1 accuracy compared to Kubios software at this time (using the same detrending method as Kubios). See below
 
 
 
Artifact detection file:




Cross comparison of Runalyze, Kubios and Fatmaxxer

What is the accuracy issue with HRV logger?

  • Update 3/23/22 - As discussed in this post, alternate preprocessing methods other than the type used in Kubios (detrending method - smoothness priors) may lead to DFA a1 results that are different than seen with Kubios software.  HRV logger does use an alternate method.  Therefore, results may not agree well with published studies.  If possible, a secondary check using Runalyze, AIenduance or Fatmaxxer is recommended.

Is there a Garmin data field I can use for DFA a1 recording and display?

Can I do a short, fast, rapid rise ramp?
  • Possibly, although most ramps are done with a 5 to 10w/min rise, you may be able to use the 30w/min protocol - see DFA a1 HRVT and Ramp slope 
How do I set up an aerobic threshold test in Runalyze?
  • Just perform a typical ramp of 5 or 10 watts per minute in Zwift.  Try not to include the warmup, or post ramp data.  Here is a guide for Runalyze ramping.
Can I do a ramp and use Fatmaxxer to get the HRVT?
  • Sure - just plot the DFA a1 and HR in the "Features" file.
  • Over a series of many "agreement" comparisons, Fatmaxxer appears to track very closely with Kubios HRV software.

How do I reproduce your published study protocol?

  • Here it is:
  • The following procedure was used to indicate at what level of running intensity (as VO2 or HR) the DFA a1 would cross a value of .75: DFA a1 was calculated from the incremental exercise test RR series using 2 minute time windows with a recalculation every 5 seconds throughout the test. Two minute time windowing was chosen based on the reasoning of Chen et al. (2002). The rolling time window measurement was used to better delineate rapid changes in the DFA a1 index over the course of the test. Each DFA a1 value is based on the RR series 1 minute pre and 1 minute post the designated time stamp. For example, at a time of 10 minutes into the testing, the DFA a1 is calculated from the 2 minute window starting from minute 9 and ending at minute 11 and labeled as the DFA a1 at 10 minutes. Based on a rolling time recalculation every 5 seconds, the next data point would occur at 10:05 minutes (start 9:05 minutes and end 11:05 minutes).
    Plotting of DFA a1 vs time was then performed. Inspection of the DFA a1 relationship with time generally showed a reverse sigmoidal curve with a stable area above 1.0 at low work rates, a rapid, near linear drop reaching below .5 at higher intensity, then flattening without major change. A linear regression was done on the subset of data consisting of the rapid near linear decline from values near 1.0 (correlated) to approximately .5 (uncorrelated). The time of DFA a1 reaching .75 was calculated based on the linear regression equation from that straight section (Figure 1b). The time of DFA a1 reaching .75 was then converted to VO2 using the VO2 vs time relation, resulting in the VO2 at which DFA a1 equaled .75 (HRVT). A similar analysis was done for the HR reached at a DFA a1 of .75. First, ECG data from each 2 minute rolling window was used to plot the average HR and DFA a1. The HR at which DFA a1 equaled .75 was found using the same technique as above, a linear regression through the rapid change section of DFA a1 values of 1.0 to below .5, with a subsequent equation for HR and DFA a1 (Figure 1c). Using a fixed variable of DFA a1 equals .75, the resulting HR was obtained. The HR at DFA a1 .75 (based on ECG data) was then compared to the HR at VT1 GAS obtained from the metabolic cart data (based on the Polar H7).

How do I make sure I'm really doing a recovery ride on my rest day?

  • This is an ideal scenario for the the real time apps.  Just watch the live read out and keep DFA a1 above .8 or even .9 (yes .75 is the cutoff, but there is individual variation and a small buffer is advised).  A single value that falls below .75 then normalizes where it started again was probably due to an APC.
  • To train hard or not, that's the question 

Are my values going to be the same day to day?

  • Probably not.  Although they may be close, it's normal and expected to have some shifting in heart rate or power on a day to day basis.  This would be the case with gas exchange or lactate as well.  As stated above, other factors will change the index result, especially heat, skin temp and humidity.

Can the intensity of exercise where DFA a1 = .75 be used as a way of tracking fitness changes after training?

  • we are currently looking at this and I will update when I am able.

I'm on beta blocker therapy, will this change the DFA a1 to intensity relation?


Why are my DFA a1 values too high for the level of effort I am doing?

  • The most common reason would be the effects of high rates of missed beats in the RR sequence.  Although programs like HRV logger auto correct for artifacts, they don't tell you how many.  Kubios will give you artifact rates - you should not trust rates beyond 5% as per our Sensors study.
  • Different detrending method used.  This is possibly why Fatmaxxer, Runalyze and AIendurance are the most accurate (in my hands) options aside from Kubios.
  • Update 3/23/22 - As discussed in this post, alternate preprocessing methods other than the type used in Kubios (detrending method - smoothness priors) may lead to DFA a1 results that are different than seen with Kubios software.  HRV logger does use an alternate method.  Therefore, results may not agree well with published studies.  If possible, a secondary check using Runalyze, AIenduance or Fatmaxxer is recommended.

Can I use the DFA a1 as a way of checking my respiratory compensation point, MLSS, VT1, LT2?


  • However, you are going to need very clean, artifact free data with an accurate device. We have not validated the Polar H10, but that's what I have used personally with reasonable results.
  • Please read the above article from JFMK for details

Where does the DFA a1 value of .75 actually come from?  Why doesn't it vary person to person?

  • Initially, the .75 value was "guesstimated" from data showing that DFA a1 runs about 1 during very light exercise (representing very correlated/self similar patterns) but drops to .5 (corresponding to random beat patterns) at very high intensity.  Therefore an in-between point of .75, could represent a moderate effort.  Looking at previously published data by Gronwald, Hautala and Blasco-Laforga shows a DFA a1 of about .75 lying in the area where the AeT should be.  We went on to show that in recreational runners, an a1 of .75 is a valid surrogate (on average) for the AeT.  
  • A key advantage of the a1 is it's dynamic range - whereas other HRV indexes hit a nadir at the AeT, the a1 value is at it's midpoint and will continue to fall past the AeT. 
  • The other important consideration is that no calibration is needed.  These are dimensionless values, so my value of .75 represents a similar physiologic state as yours (partiality correlated) .  Of course since it represents net "organismic demand" and status of the autonomic nervous system, there can be day to day fluctuations and effects from fatigue, stress, temp etc.  
  • Heart rate and power, although great metrics, can't be used for accurate zone assessment, unless one calibrated them to a lactate or gas exchange test.  The closest parallel example to a1 would be lactate (a measure of internal metabolic status), but even that has very wide variation in levels at the MLSS.
  • All these factors result in our ability to use the index for intensity assessment while exercising.

 I've noticed that I can't drop my a1 below .5 using the HRV logger, any ideas.

  • Yes - see this
    DFA a1 agreement using Polar H10, ECG, HRV logger 
  • And the difference detrending makes
  • Use a more precise app such as AI Endurance, Fatmaxxer or Runalyze  
  • Update 3/23/22 - As discussed in this post, alternate preprocessing methods other than the type used in Kubios (detrending method - smoothness priors) may lead to DFA a1 results that are different than seen with Kubios software.  HRV logger does use an alternate method.  Therefore, results may not agree well with published studies.  If possible, a secondary check using Runalyze, AIenduance or Fatmaxxer is recommended.
  • As stated, high amounts of artifact correction can bias the a1 upwards.

Can DFA a1 be used as a marker of fatigue?

  • Yes according to out recent publication - DFA a1 as a marker of endurance exercise fatigue 
  • In short, the usual pattern of DFA a1 behavior will be shifted after a session of fatiguing exercise.  This can also be used as an indicator of "training readiness" in lieu of resting HRV.  For instance if you see that your a1 is running lower than it should in the warm up period of your session, that may indicate that you are still recovering from a previous stressful set of session. 
  • See the AIEndurance web site for their implementation of this concept
  • To train hard or not, that's the question  
I read in (fill in the name) blog that DFA a1 insights regarding exercise intensity/threshold determination are based on "flimsy" evidence - what do you say to that!
  • To date, no published study has proven any of our conclusions false.  In fact another group, working with a large number of participants found essentially the same results regarding threshold values.  When reading someones personal experience, several prerequisites should be present - the use of Kubios as the HRV interpreting software, publication in a decent peer reviewed journal and no financial conflicts of interest.  Unfortunately, the later should not be underestimated as a motivation to discredit DFA a1.

Does the HRVT (a1 derived AeT) change if I'm sick?

  • It probably depends on how ill you are - anecdotal reports have appeared showing substantial a1 suppression at low exercise intensities.  
  • Given the known effects seen with fatigue, it would make perfect sense for the a1 to be lower than normal during or immediately after an illness.
Will a Covid vaccine change the a1?
  • We really don't know.  But a recent observation I made might shed some light.  I did a 20 minute Zwift ramp (130 to 230w) the morning of my second Moderna Covid vaccine (Pre) and another the next morning afterward (Post).  Yes, I had the typical post vaccine sore arm, nausea, fatigue, muscle pain and was really "spaced out". Like the flu but no sore throat or congestion.  Did the HRVT change?  Very surprisingly it did not:

The time/power at crossing a1=.75 was just as it usually is 210-215 watts.  N=1 data certainly, but intriguing that a1 seems fairly well linked to exercise load, at least in the short time frame - I wasn't up to going on for another couple of hours to see what would happen.

Why does my DFA a1 seem lower (for a given HR) running vs cycling?

Several potential reasons:

  • Random differences and day to day variation - try to repeat the tests on a regular basis to see if it is real.
  • Potential loss of R peak precision. What I have found is that in certain people (a minority) some electro-mechanical factor creates some distortion of the R peak. This may be diaphragm related but more likely trunk musculature that is firing more strongly while running. If you wore the Movesense ECG you may see this:

instead of this:


 

  • Since the DFA a1 is related to "correlation" of beat patterns, having a loss of precision of those patterns by distortion of the R peak will reduce the value seen. This was nicely demonstrated by Dr Mourot's study
  • This will not affect the HR since the same beat count per time is present. It also is not noticeable at rest since those offending muscles are not firing. 
  • If you see a large discrepancy and don't have the ECG to confirm why, trust the bike data over the run until we get more information on this problem - again, it occurs but not in everyone. 
  • This is a more detailed discuss
My DFA a1 drops to very low values with low intensity cycling - why?
  • The most common reason is that of poor waveform signal to noise ratio (see immediately below about belt position).
  • Illness, stress, fatigue, over-training
  • Certain artifacts and cardiac rhythm disorders (atrial fibrillation) - this is more common than you might think.

Does the position of the HRM belt matter?

 

Can the index be used for monitoring endurance and HIT fatigue

Can I get a single lead ECG from a Polar H10 sensor?

Is the HRVT concept valid in non athletes or those with cardiac disease and beta blocker therapy?

Some final thoughts are presented in this post as part of the Frontiers Review article.
 
 
Heart rate variability during dynamic exercise


 

81 comments:

  1. What would be a good power between “steps” using HRV logger and the six minute long steps? 10 watts? 20 watts?

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  2. I think 20 watts should be fine. Once you get your approximate threshold, you can retest by just doing 3 stages, AT-20, AT and AT+20w.

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  3. Hey Bruce,

    Great blog! I am a nephrologist passionated about endurance training :-). I even did some of my training in Gainesville back in 2005-2007!
    I am going to try to use DFA a1 to estimate my LT1 tonight!
    Thanks for sharing the information.

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    Replies
    1. Thank you for your kind remarks, glad this method may be of help to you. And yes, greetings from Gainesville!

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  4. Bruce, thank you for your work, so helpful. I'm using HRV Logger, Kubios-free and runalyze to establish my LT1, using your protocol: 20' wu, 6' steps with 0.3 km/h increments. I noticed that DFA cross .75 value, but then rises up, for 20/30 minutes (even if HR, speed and fatigue is high) Actually it seems that 133 bpm and 156 bpm are my aerobic threshold. I know it is very weird, can you hepl me to interpetrate ?

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    Replies
    1. Could you send a dropbox link to the rr data so I can take a look?

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    2. No problem
      https://www.dropbox.com/s/rsdxkpxs3upegrn/2021-3-7_RR_Calcolo%20Lt1.csv?dl=0
      I have also all the files exported via HRV Logger

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    3. Thanks, ignore the early dip, analyzed and put on twitter

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  5. This comment has been removed by the author.

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  6. Hi Bruce, thanks for replying on Twitter, really appreciate it. However, 140 characters is just not enough.
    I'm really enthused by the science of DFA alpha 1 and have just listened to the Endurance Innovations podcast where I'm very pleased to say I understood all of what you said.
    One question came to mind while I was listening (and cycling), what would be the effect of wearing 2 HR straps simultaneously? Have you ever tried this?
    Also, I was going to do the testing sessions as workouts in TrainerRoad but now I'm thinking that I'll keep it simple and just send a workout to my Garmin and do it from there. This way it will keep the connections to devices to a minimum (Garmin, TrainerRoad, smart trainer, Android app would all need to be used otherwise). I assume you would concur with this approach.

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    Replies
    1. Thanks for the kind words. Although 2 straps can be used, if they end up bumping together that could produce artifact which we want to avoid. Your best bet (and what I do) is use a Polar H10. You have 1 bluetooth to Garmin (that's what I use for kubios), 1 bluetooth to another device for accurate RR (I use HRV logger realtime), and unlimited Ant+ (trainer road, zwift, android ipbike etc).

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  7. Yes I wish I'd bought the H10 now for that reason but didn't give enough thought to how I'd connect and to how many devices etc. Ah well, I'll manage.

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  8. Good blog and information. I started using the hrv logger, 3 days ago and I think my LT1 is 133bpm. As I trained in the mountains I accumulated a lot of fatigue and I think that at 155 bpm the value of alpha 1 appears 1.20. I encountered the same problem. Can you help me?

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    1. Thanks, not sure I totally understand. But after HIT or long rides, all bets are off on a1 thresholds. It will seem lower than usual at a given power. Remember to discard data if artifacts are above 5%

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    2. Thanks 🔝
      I saw in hrv logger the artefacts are above 5%. In relation to my doubt it is in trail running, when I start on the flat the alpha 1 is 0.75 {133bpm} but when I go up, logically my hr goes up {155bpm} and my alpha 1 is 1.20. I think more beats per minute my alpha 1 goes down, if the exercise is more intense

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    3. Artifact correction can raise the a1, especially if the a1 is around .75 or lower. So if you hit a1=.75 at a HR of 133, then starting getting >5% artifact at higher HR, the a1 would rise erroneously from the artifact correction effect.

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    4. Now I get it!
      what is your opinion about a protocol before a 50k test with 2500d +? In the warm-up before the race some run with increment?
      Other things, I train a lot my MFO {max fat oxidation), the intensity of a1=0.75,is the point of fat max? thank you very much from Portugal - Porto, send my our address and I sent to you a bottle of port wine

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    5. Ha, thanks, my reward is seeing you get the hang of this. As far as training, that's a tough one. I'm not a coach and I'd hate to give you the wrong info.

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  9. Great work on all of this! I am trying to work on the difference between my a1 running and cycling. I see your comments above. How would walking come in to this? I noticed today on a run, that when I was walking up a hill, to keep my heart rate the same as when running, a1 went up to what seemed a more appropriate level (generally it is too low running - around 20 BPM below cycling). Would the difference between running and walking fit with your theory as to why there is a discrepancy?

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    1. Yes, good observation. Walking up a steep grade or even a stair stepper would be a good way to estimate your running threshold. It seems that the act of foot strike/body impact creates some electro mechanical artifact causing loss of R peak precision, resulting in a low a1 (loss of "correlation" patterns)

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    2. Great thanks. I have a stepper so will give it a go!

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    3. Please let me know how it goes.

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    4. I did a test today on a stepper (actually it is an elliptical trainer so uses arms as well). I did 4 min warm up and then 4 mins ramps trying to keep HR at 115, 120… to 145. I then did exactly the same test on a treadmill. The a1 results seem very different and a bit strange!. For the stepper, a1 never got down to 0.75, with the lowest being 0.9. For the treadmill, a1 was never above 0.75 (except for the warm up which was partly walking). Using a Polar H10, data doesn’t look too messy. I am looking at the data in Runalyze and Kubios (free) so difficult to do direct time comparison other than in the 4min blocks. So, for me definitely seems to be a problem looking at a1 when running. Not sure why I wasn’t seeing a1 going below 0.75 on the stepper. You are welcome to the FIT files if any use.

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    5. That's exactly what I'm looking for. If you could send me a dropbox link to the fit files I can do a formal comparison and post that here. I did a podcast a couple of days ago and part of the discussion was on the issue of early a1 drop in some runners. Thanks.

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    6. I listened to the podcast, very interesting. Link is https://www.dropbox.com/sh/0xtctaiyyglg6sw/AACflqzlutKBxeBwuEj_0UdYa?dl=0

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    7. In case it is useful for comparison, I have also uploaded a bike test I did a couple of weeks ago. This was 10 min warm up , then 5 bpm heart rate ramps of 6 mins, to 120 bpm to 150bpm with 8min warm down

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    8. Got them, will work on a formal comparison and let you know shortly - thanks! Yes, the bike is very helpful.

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    9. Here we go - http://www.muscleoxygentraining.com/2021/03/dfa-a1-problems-during-running-why.html

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    10. Great thanks! Really interesting. I am still surprised that the Stepper results seem higher than I would expect. I have been doing MAF training for the past 5 years or so and my MAF is around 130 which always felt right and I had assumed that things would align around there somewhere. Guess I just keep exploring! Keep up the good work.

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    11. I got an H10 and cannot get a stable DFA a1 while on treadmill (seems too low, I have to walk to stay above threshold) While on a smart trainer I cannot Get it under 0.90 until I am at 160bpm, 91% of my HRmax (i'm 48)
      What can I do to determine my LT1 ?
      1 - treadmill but with bruce protocol for ergometer test (3% incline every 3 minutes) ?
      2 - trust the bike readings of DFA a1=0.75 ? (seems too high for me)
      3 - non of the above, just run with the talk test ?

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    12. I understand that there are a lot of protocols for treadmill tests for athletes: Bruce, Ellestad, Balke, each one with thei own modifications.
      To avoid early DFA a1 decline, what would be a treadmill protocol suited to get true readings ?

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    13. See my comments in the other post about why the run measurement may be an issue. Try either an elliptical, stair stepper or bike to get the HR at a1 = .75. If the bike seems too high, do it a couple more times to confirm. Lastly, some people may simply not get perfect agreement.

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    14. I already saw it, and for me it is mandatory to find hte correct AeT
      I will follow your protocol on bike one again using Zwift and Elite
      Could beta blockers be an issue ?

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    15. Let me know how you do. Beta blockers are probably not the issue, I originally did a case report on/off Atenalol to see if a1 behavior changed (it did not). Some unpublished data also suggests that they are not a factor.

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    16. I just tried another little test. I did a walking 4 min HR ramp up a hill. The data looks like it agrees with bike/elliptical data. I need to find a steeper and longer hill to try and get to a1 = 0.75 as I couldnt get HR high enough. Looks like it could be another option for anyone who has incongruous running data and may not have access to other equipment.

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    17. Good idea, thanks for the feedback

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    18. spookymuggs, I did quite the same as you: treadmill, fixed speed at 5.5km/h, incline at 0.5% to start, then +0.5% every 6 minutes. DFA went down to 0.80 but then rose up again after 75 minutes with a 8.5% incline and I stopped

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  11. I was trying to investigate a bit further and found there are a couple of apps that connect to the H10 and give an ecg trace. I wondered if they would give any useful information if I tried to capture when running? I have uploaded a screen recording in the dropbox folder above. Let me know if you think it could be useful or not.

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    1. Now that's cool! Although exciting, I looked at a related app specs, and the sample rate is only 130 Hz - way too low for wavefrom analysis (need at least double that, 500 Hz is even better). If you are worried about an arrhythmia it seems useful, but then you need to be trained to read a rhythm strip. I am going to look at it further - thanks again. Will report back.

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  12. This is really interesting research. I've tried multiple straps and apps (Kubios & KRV Logger) but it's very challenging to get my a1 below 1.0

    I got it below 1 during a very tough Vo2 interval session. But Tempo power seems to be around 1.4 for me. Do you think some folks might have a different metric? (I've used a Polar & Garmin strap)

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  13. Which Polar are you using, and are you using bluetooth for the recording?

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    1. I've used both Polar H10 & Garmin HRM-Duel, both via Bluetooth for sure - with HRV Logger.

      It might have used Ant+ for the analysis I did in Kubios - that was recorded via a Garmin Watch (paired with the Strap). Not sure what the Garmin watch uses.

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    2. You need to delete the ant+ hrm in Garmin settings and re pair as bluetooth only. Record a ramp to almost max, send me the fit file and I'll be happy to review it with you. Please use the H10.

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    3. Thanks! I'll give that a shot this week and put on dropbox.

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    4. Looks like my watch (Fenix 3) only supports Ant for the HR strap. Would recording via the HRV Logger be OK?

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    5. Yes, the HRV logger is fine. Use the workout mode for artifact correction, 2 min windows and you should be good.

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    6. Think I'm there now. I did 4 min steps and increased 10w each step. FTP is about 200, max HR is around 190. I was a bit nervous so HR felt a tad high at the start, then was about right when I hit 200w. I've included the HRV Logger detail as well as the Zwift FIT file with power data & HR.

      https://www.dropbox.com/s/0n7mf5cmdk020tu/HRV_data_010421.zip?dl=0

      If I had to guess based on breathing I would say LT1 is around 140w, but interested in what you think! Thanks again for looking at this data.

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    7. See my latest post for details - I get much higher than your numbers.

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    8. Wow, thanks. Appreciate that. Very interesting

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    9. This could well be a dumb question as am getting out of my depth.... but I looked at this data in kubios (free) as I am still trying to get my head around all this. When the data is divided into the 4 minute ramps, around ramp 6, the poincare plot starts to show strong linear patterns that get more distinct as the ramps increase. I havent noticed this type of thing before and wondered if it had any significance?

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    10. I know what you are describing - I'm not sure what it represents, but I see that commonly. It could be a restricted set of values, so they are segregated together.

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  14. Nice blog, I am digging deep into it and awesome work! I have been using a polar H10 for months by now and recently found out about DFA. I went looking into past running/cycling workouts in the runalyze platform but I found out that most of the recordings have a lot of artifacts and hence are not reliable. I always used a BLE connection on my Fenix watch. What could the problem be? A faulty strap? Or am I not positioning the strap properly on my chest (although HR readings never gave me issues apparently, except for running where at times where it loses the signal, but it happened only in the last month)?

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    1. Your best bet is to use one of the iOS or android apps that will record an ECG from the H10 - that way we can see if it's noise or an arrhythmia. http://www.muscleoxygentraining.com/2021/03/polar-h10-ecg-tracing-short-how-to-guide.html You could also use Fatmaxxer as that will capture the artifacts as ECG snips as well. After you do that, I would be glad to take a look for you

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  15. Great work,
    I got interested in DFA analysis, So I bought a polar H10. and did a quick test using BLE connection with my garmin (DFA was also real-time viewed with fatmaxxer). My known FTP is 168 watts, so assuming my LT1 to be somewhere around 120, after 5 minute warmup, I did a quick ramp from 90 -> 140 watts over 10 minutes (5 watts/min). I cut the warmup part and results were sent to runalze. my DFA remained over 1.0 over the entire session, going nowhere near 0.75... (it was also seen with fatmaxxer as well...)

    I then did a full ramp (MAP test) trainerroad again gave me FTP of 168, my DFA went to 0.75 at 185watts/166HR, wich is even higher than FTP and hit 0.5 at 220watts/188HR, almost near my failure point (230 watts)
    The real time DFA values looked similar on fatmaxxer.


    The results clearly are off... the DFA alpha 1 values seen to be calculated too high for me. I had a though on this, and possible causes could be.
    1. My difference from study population made the bias?
    - study done only in caucasian population? I am asian.
    - study done only in trained athletes? I am a recreational rider with around 5~8 Hr/wk training
    - my minor arrhythmia (1st degree av block)? although it does not need medical attention, the prolonged PR interval may have some influence in DFA?

    2. Something wrong with my protocol
    3. My polar H10 could be faulty? [ Though less likely, as it is new... and the HR values seem correct, and SDNN values are in line with my old garmin HRM (ant only), and Artifacts: 0,0% on the log and no artifact on fatmaxxer]

    I would appreciateyour insights.

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    1. Thanks for your comments. There should be no issue with ethnicity, age or training status. I am curious about the AV block and/or QRS complex effects on the a1. Can you send me an ECG recording from the H10 - you can use either Polar equine or Polar sensor logger from the app store.

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    2. OK i'll get a log and get a ECG recording tonignt. How can I send you a file? I can't find any email address on this blog

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    3. https://www.dropbox.com/t/uv1pkpk8fImNzNu8

      includes: ECG data created with Polar equine (resting), 10 minute steady ramp (LT1 determining), MAP test, and a low-intensity workout done today (with DFA values over 1 all the time)

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    4. I reviewed waveform and it's fine. I also plugged your ramp into kubios and the HRVT was about 160 bpm. Given your max HR at 195 bpm, that's not totally unreasonable. Using the SDNN nadir as a measure of HRVT, it also agrees with the a1 calculation. So by autonomic physiology standards your AeT is about 160 bpm. See the end of http://www.muscleoxygentraining.com/2021/04/quick-look-at-someones-ramp-data.html for the graphs.

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    5. Thank you for your review.. although "power" wise it still doesn't seem to make sense, in tearms of aerobic HR threshold, I see the point and that it makes sense. I'll do some more review on this topic and see my DFA trand over more workouts.

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  16. Very interesting blog. Maybe I'm an outlier, but I measure my Lactate levels at the end of every workout which is on a stationary bike in "constant wattage" mode and usually lasts an hour. I'm trying to end up in a range of 1.5 to 2.0 mmol of lactate. There is some variance and I was looking at using fatmaxxer to help dial-in my workouts, but it doesn't seem to work for me.

    Despite working out at a constant 165 watts (with about a 10 minute ramp up at the beginning), the DFAa1 ranges between 0.4 and 0.6 in one session, and 0.35 and 0.45 in the other session. From what I've read, this shouldn't be happening. I should be well above my lactate threshold according to my DFAa1, but my actual lacate readings were 1.5 to 1.8 mmol.

    If I try to modify my workout and decrease power to get my DFAa1 to the 0.7 to 0.8 range, my lactate will be down near 1.0 mmol.

    I'm using the Polar H10 connected via BLE and don't seem to have many artifacts.

    My nighttime HRV per my gen3 Oura ring is in the single digit number of milliseconds (the gen2 ring had me at around 12 to 14ms avg HRV). Could it be that this DFA analysis doesn't really work for someone with such a small HRV or I have some other issue going on?

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    1. Hi Mike, sometimes the h10 needs to be rotated a bit to get an optimal signal. Can you share a link to the fatmaxxer .ECG file for me to see if that's an issue?

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    2. Although I have the app in Developer mode, I don't see any ecg files. I just see the rr, debug, and feature files of the last couple days. Do I need a later version than what's in the Google Play store?

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    3. Yes, go to https://github.com/IanPeake/FatMaxxer/blob/main/app-debug.apk and hit the download button on the right side of the screen (you may need to remove the playstore version to install this apk). Or use the app mentioned here - http://www.muscleoxygentraining.com/2021/03/polar-h10-ecg-tracing-short-how-to-guide.html

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    4. I've had a bit of adventure today, so I'm going to post the details in case anyone else runs into the same issue. I also posted this in the fatmaxxer github comments.

      I can't sideload apps because I use my phone for both personal and work use and work makes me install a mobile device management program that won't let me side load apps for security reasons. I have an old android tablet somewhere I could use if we can't make headway otherwise. Fortunately I've been using Polar Sensor Logger for my workouts for several months, so felt comfortable that I could do that--until I couldn't.

      The polar sensor logger app wouldn't create or graph an ecg file either. It's Google Play page says it needs firmware version 3.0.35 or later. I noticed that I was on 2.1.9, but the Polar Beats app wasn't offering an update. After scrounging around on the internet, I found others with the same issue and apparently you have to also download and install the Polar Flow app and create an account and then the Flow app actually offers the update. I did all this and it offered two updates in a row and now I'm at version 3.1.1.

      I immediately started fatmaxxer and saw it created an ecg file. I did this 2 or 3 times and saw 2 or 3 sets of logs including an ecg and figured my problem was solved. I went down on my bike to do a quick workout under load and capture an ecg file to reference here. Unfortunately, it didn't create one for that workout (so there is some residual ecg save issue). I was able to create an ecg file in the polar logger sensor app, or at least appear to. It will run for a bit and will say "waiting for ecg" and then after it started to display a number (some number of microvolts), it would run for 5 seconds more and hang up.

      Ultimately, I got some ecg files from both apps, but not necessarily while working out. Trying to view the fatmaxxer apps in excel doesn't look quite right since their seem to be multiple readings for the same timestamps. I'll post some links here and hopefully something in here will make sense.

      From fatmaxxer:
      https://drive.google.com/file/d/1q1cLlDml0779La9tnMcuoASDeKynZPAN/view?usp=sharing
      https://drive.google.com/file/d/1pl-4XKkfri6wGKYhWoukrzbOeV1eA4Il/view?usp=sharing
      https://drive.google.com/file/d/1pPKdk50yL5DTfDQMgw2JI6GxVJ_YkPxL/view?usp=sharing

      From Polar Sensor Logger:
      https://drive.google.com/file/d/11P04qQSO5ZhJn7ul4ixr1hS6tm_QWLjo/view?usp=sharing
      https://drive.google.com/file/d/11Gf5WkHB7muJQQpXKtOTLkIrSbHbIQ-6/view?usp=sharing

      One of the fatmaxxer files looks like it starts out very large and then has an exponential decay to a steady state. I had one episode where I got several artifacts as soon as the session started, but then they stopped and got zero more after that.

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    5. Sorry you had to go through all that - whew! However we now have the answer from your efforts. The ECG is inverted, either from having the polar module upside down or having a non standard cardiac axis. I have a post on that with some examples - http://www.muscleoxygentraining.com/2021/08/dfa-a1-and-optimal-hrm-position.html. I'm going to update that post with your data once we get this settled (if you don't mind). Suggestions - first try inverting the module (Polar name upside down) and save a Fatmaxxer ECG file. Then, with it inverted, move it left 1 inch and record another Fatmaxxer ECG - send me both and we will pick the best one (highest R peak). For now I added your ECGs to http://www.muscleoxygentraining.com/2021/04/quick-look-at-someones-ramp-data.html (the last case).

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    6. I'm happy to have you post my data. Hopefully it helps someone else get this working too. This is huge deal. Thank-you for the help and all that you are doing with this DFAa1 concept.

      Here is an ecg file from snapping the sensor into the strap upside down centered on my chest (fatmaxxer locked up after about a minute and a half):
      https://drive.google.com/file/d/1sYUO4EGtNXxd3eW2jygdO71V61sXUoOM/view?usp=sharing

      Here is a file after moving the sensor an inch to my left with the sensor still upside down:
      https://drive.google.com/file/d/1sry7oGPE-1Elluo3_aZJ5ZWtSgnWwSBI/view?usp=sharing

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    7. Both inverted are similar but the centered is slightly better (?). Signal to noise ratio improved but try to use some conductive cream under the sensor pads (moisturizer works fine) for optimal signal strength.
      I'll put the pictures in the same place as the first screenshots for you to see. Last piece of the experiment - do a ride under the same conditions as before (a ramp and/or power about 165w) - we will see if the numbers are better.

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    8. Thanks Bruce. I'm headed to the CES show in Las Vegas for the rest of the week. I'll try a workout when I get back to see what's changed. I've got conductive cream that I used to use with a different sensor a few years ago, although with these workouts I seem to be sweating enough and reading heart rate was never an issue with the H10. I guess we're trying to suss-out more information and need more signal instead of just heart rate now.

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    9. After drinking and eating too much, being jet-lagged, and probably being exposed to COVID during the previous 5 days, I was going to do a ramp test to check out wearing the Polar H10 inverted. I started 30 watts below my normal LT1 level of 165 watts. After 10 minutes at 135 watts, I was already at 2.1 mmol of lactate. My DFAa1 was .7, so even though my lactate shot up, this was encouraging as far as getting a useable signal goes. I added 10 watts to see where this would go and my lactate increased to 3.1, but so did my DFAa1 to 1.05. Added 10 more watts and my lactate rose slightly and DFAa1 rose higher. I then dropped back to 145 watts for the last 30 minutes and took a couple more lactate readings.

      Excel with graph of HR and DFAa1 and including table showing time, wattage, HR (2 min avg), DFAa1 (2 min avg), and lactate: https://docs.google.com/spreadsheets/d/18OIQYmPpluLW4NTFdWmY-ifBP8EPxwhJ/edit?usp=sharing&ouid=103340134804964568090&rtpof=true&sd=true
      features file: https://drive.google.com/file/d/1wCUSeZhrInw43F5PE4MoBA4nXCzQ6gLm/view?usp=sharing
      ecg file: https://drive.google.com/file/d/1wP4Xwt_n5JNJQccAM_YIZ1XS4Z_UTkEF/view?usp=sharing

      This morning, as I suspected, my lactate threshold improved with better sleep, no alcohol, and the workout yesterday. I warmed up for 15 min and made the ramps longer--9 minutes at power instead of 5 and measuring every 10 minutes (1 minute used measure lactate and record everything then change the power). I noticed yesterday I introduced artifacts while measuring lactate, so I changed the process and things settled down some. There was what I think was a PVC at about 45 minutes (I think I see it in segment 6). I had these about a year or two ago at rest, but they've largely gone away (with Mg and getting my thyroid under control). I've never felt one during exercise before--much more dramatic.

      Excel showing data table and graph: https://docs.google.com/spreadsheets/d/18VV6F50j0RTSzLsWJ4EjRzVHksOCVLnB/edit?usp=sharing&ouid=103340134804964568090&rtpof=true&sd=true
      features file: https://drive.google.com/file/d/1xe53oVyui7Fk9gHIeLyzBkXzfKgczo9e/view?usp=sharing
      ecg file: https://drive.google.com/file/d/1xixj3weTWUp_yb9FwIv_JZKXBzU8qgaN/view?usp=sharing

      I used conductive gel and with the H10 inverted, I'm definitely getting better signal. It seems like it's behaving better, but I'm not sure I can use this to fine tune my workouts. Today was a pretty good structured data set. The last 30 minutes of yesterday's workout and the last 15 minutes of today's were under constant load, but the DFAa1 seems to swing 0.40 over that time.

      I'm 63 years old. Prior to the pandemic, I was doing HIIT on the bike at the health club for the previous 3 years or so and no aerobics. Then stopped doing anything for almost a year during the pandemic. Then got a bike for home and started doing what I think are your Zone 1 workouts ( Iñigo San Millán's Zone 2 in 5 zone model). I went from an LT1 of 110 watts on March 1st to 165 watts on August 1st where I've plateaued. I've had zero reduction in resting heart rate or HRV in that time. It's normally around 72 at rest during the day and my Oura says it gets to the low 60's at night. So my lactate responded as you would expect (4 hours or more a week). My heart, not so much.

      Per your latest post, I think I'm definitely getting better signal with the H10 inverted, but I think I have some other issue going on with the HR and HRV. If there is discordance, do I train using lactate (which is a pain) to get better metabolically, or do I follow the DFAa1 and perhaps get better cardiac system benefits? Perhaps pushing harder to LT1 is going past where it's beneficial to my heart because it's more chaotic?

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  17. I somehow posted the wrong link for the first Excel file from 1/9/2022. It should be this one: https://docs.google.com/spreadsheets/d/18NS8LaLAPpAbcZlhsRco1nYO8gfTwN_T/edit?usp=sharing&ouid=103340134804964568090&rtpof=true&sd=true

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  18. Hi Mike, I looked over your ECG files - the signal is better, no severe arrhythmia that I can see but you should use the newest fatmaxxer as this puts a marker between "snips" so it's easier to see whats happening. Signal is good, near 1000 uV. The first day back after your trip was interesting. The higher than normal a1 is from excess artifact correction (I added the screenshot to your case study), but the a1 is about .75 during clean parts. That is in keeping with the lactate about 2 mmol. You did get down to about .6 DFA a1 toward the end. The second session had fewer artifacts and a1 was between .5 and .8 (graph added on your case). HR was pretty stable except for that interval with lower a1 values. I would view this as a sign that your autonomic NS is still a bit "stressed" from everything you mentioned. At this point I would trust the a1 for thresholds once you return to well rested normal (since we optimized the waveform voltage). Remember - it's also used for indicating fatigue - if your numbers are unusually low. I'm about your age and I do 90% of my training in zone 1 (a1 >.9) and the rest HIT twice a week. Recovery gets harder each year. You want high volume, low intensity, if you can manage the time. We are learning that pushing hard efforts when your ANS is showing stress may not be optimal - so I go by a1 rather than lactate or muscle O2 breakpoints. When we were 20 years old, it may not have mattered much, but at our age, recovery is key. I did not see any VPCs, but if you spot anything, send them my way.

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  19. Thanks Bruce. All other things being equal (other stressors are "normal"), do I need recovery from zone 1 training? Can I do it every day? I'm assuming I only need recovery from HIIT or an actual ride.

    My oura is always nagging me about HRV, but I figured I can still do zone 1 regardless. Should I take more days off?

    Prior to lactate and now DFAa1, my best guess was Maffetone's range, but even that is a rubric. For me, that would be about 118 bpm and he would want me to take off 10 beats for being on daily meds. Using lactate, I make some pretty quick progress and my heart rate at LT1 was in the low 130's and during summer, even with a fan blowing on me it would get into the mid to upper 130's.

    I tried to back off in yesterday's workout and keep DFAa1 higher. I ended up at 10 watts lower than my rested normal, but was only 1.0 mmol of lactate. Definitely easier. Am I going to lose conditioning this way, or will I facilitate batter recovery and ultimately a higher HRV and lower heart rate?

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    1. All good questions. Personal factors such as muscle fiber type, SNP variants, recovery ability all play a role. Even zone 1 volume can add to the "fatigue" load depending on your status. Your concerns mirror mine, and it's difficult to answer. Everything contributes to "load" including resistance exercise, long walks, extensive yard work etc so riding in zone 1 may not be too much depending. I would suggest taking 2-3 days off, no alcohol, plenty of sleep then do a baseline ramp to get some thresholds. See how that looks then begin some polarized training (even 95/5 easy/HIT) and follow the ramps every couple of weeks for progress. You will not lose conditioning by avoiding excess volume/intensity if you are careful. What you don't want is to over reach - you are better off on the other side of the spectrum (at our age). So keep the a1 above 1.0 on easy days and when you do your HIT, really blast it (but not too often). Hope this helps -

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  20. Hi Bruce,
    Has respiration rate been incorporated into the DFA a1 studies? It would seem like a good metric to narrow down the VT1 and VT2 window levels.

    The Frontier X monitor measure respiration rate this but I cannot use with HRV logger since it does not send out RR signal.

    https://fourthfrontier.com/pages/know-the-science


    Frontier sighted the following white paper.

    https://www.frontiersin.org/articles/10.3389/fphys.2017.00922/full
    Thanks.

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  21. Resp rate data is now incorporated into kubios and appears pretty accurate. No, we have not looked at this in terms of a1. I am sorry but know nothing about that device.

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    1. Would that be kubios Premium or free.

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    2. The Frontier x device records ECG 24/7 as a hear monitor strap. I asked the company to add RR Sending signal to be added to device in order to work with HRV Logger and other HRV apps

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    3. Premium https://www.kubios.com/respiratory-rate-algorithm-validation/

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