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Tuesday, December 29, 2020

Active Recovery Day 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.

 After doing some tough intervals and testing yesterday, my goal today was to just take it easy and recover with 90 minutes of easy cycling.  I also wanted to try the HRV Logger  "exercise mode", using the more aggressive artifact correction method of the software.  Test conditions were still the same, but the ride was essentially 155 watts (well below VT1) for the entire time except for an 8 minute block at about VT1 power (or slightly above it).

First the Logger View:

  • We can see that DFA a1 is well into the low intensity zone with well correlated values showing good fractal behavior (>1).  
  • The first red circle is the 8 minute interval at VT1, and indeed, the DFA a1 drops to below (or at) .75.  
  • After the interval, power resumed at very easy intensity but about 6 minutes later, the DFA a1 dropped unexpectedly.  After the brief drop, the values resumed their normal levels well above 1.  More about that later. 


Comparison with Kubios:

  • The agreement appears good between both methods.  Yes, it would be nice to have more points on the HRV Logger, but it provides useful information and helps one stay within their zone 1 range.  
  • The 8 minute interval does have finer detail in Kubios, but again, for practical purposes the Logger conveys the correct data.
  • The artifact (or whatever it is) is seen with both software methods - which is comforting.  What does that drop represent?  Is it an APC, VPC or something else?

I looked at the ECG (from the Movesense unit) and there was no arrhythmia.  In addition, the Kubios time varying plot of the DFA a1 shows exactly the same dip in values:

Whatever caused the dip in DFA a1 was present in both recordings and with no ECG abnormality.  Therefore the HRV Logger algorithm was not at fault!



  • Tracking of DFA a1 with the HRV Logger continues to provide accurate real time low intensity exercise information and should help with enforcing zone 1 training.  The observation of DFA a1 while doing a training session takes the guess work out of low to moderate intensity training.
  • The more aggressive artifact correction mode ("workout") seems to show good agreement with Kubios auto correction.  Further study of the effects of aggressive correction on DFA a1 would be of interest.
  • Occasional dips in DFA a1 can occur for no apparent reason, but they are transient, of short duration and are isolated.   

DFA a1 and exercise intensity FAQ 

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