Thursday, September 9, 2021

DFA a1 threshold in a cardiac population

Although it has been released in abstract form, our full article describing the use of DFA a1 in a cardiac disease population (CHF and stable CAD) has been published.  As I have done in prior publications, I wanted to share some individual participant data to show how things work "under the hood".  Many thanks to my co authors, Laurent Mourot and Thomas Gronwald.  

We found three important findings - 

  • DFA a1 can be used in this very different population to determine the first threshold (VT1).  
  • Beta blockade did not appear to affect the index (as discussed here before).
  • The improvement in VT1 after cardiac rehab was correlated with that of the improvement in the HRVT.  Therefore, this is the first evidence published showing a1 can be used for following VT1 related fitness status.

How did these parameters look in a single subject?  Here is one example of a participant with CHF, pre and post rehab exercise (Please read the full article for details and background).

Gas Exchange Pre (baseline)

We are using the excess CO2 method (see the article for references).  I did add HR to the plot.

  • We can see at about 300 sec into the test, the curve slope changes, at a HR of 76 bpm.  That is the point of the VT1 HR.


The Pre Rehab HRVT:

DFA a1 vs HR:

  • The HR at HRVT is 75 bpm (very close to gas exchange - but not all participants were this close).

Post Rehab Results:

Gas Exchange Post:


  • Both VT1 gas HR and HRVT HR are about the same (81-82).  
  • VT1 gas HR improved after rehab as did HRVT HR.


We presented this Figure in the article showing the individual responses (ml/kg/min, HR, watt change):

This indicates that those who had improvement in VT1 also had better HRVT metrics.  Those who did not improve with gas exchange generally did not do so with HRV either.


  • The HRVT concept holds in a markedly different demographic of participants (CAD, CHF), most of whom were on beta blockade therapy.
  • Improvement (or not) in first threshold gas exchange parameters was well correlated to that of the change in HRVT related metrics.  
  • I hope more groups consider using "correlation properties of HRV", AKA DFA a1 derived HRVT as a fitness metric to follow over time.


Heart rate variability during dynamic exercise



  1. Congrats on this paper! I just read most of your DFA a1 related blogs and it really looks like a promising value to track and use non invasive l’y to find that first threshold, as well as potentially Autoregulate training < threshold 1. Thanks for all your work!

    1. Hi Sean, thanks for your comments and reading the blog. Welcome to the dynamic hrv club😁.