Back in the "early days" of using DFA a1 for exercise threshold determination, I was approached by a developer who was interested in writing an app for Android devices that would use the Polar API to compute DFA a1 on a real time basis. In the span of just a few weeks, an impressive prototype was produced. Along the way, we learned the importance of replicating the Kubios methodology for the "detrending" step that occurs early in the computational process. Additionally, I added a few items to a wish list, including ECG snip recording when artifacts are detected and reporting on R peak voltage (also in real time). The result was Fatmaxxer, one of the best apps available for a1 recording and display. During my collaboration with the Murias physiology group, Fatmaxxer was often used for collecting raw RRs from the Polar H10. We also used it as a means for identifying the DFA a1 cutoff for partial ramp determination of the second threshold. It was during the review process for that study that it was suggested Fatmaxxer be "validated" against Kubios HRV. Thus far, no other app/web based software has been formally compared to Kubios. Given the need for a low cost solution for DFA a1 determination along with the need for real time measurements, we decided this study needed to be done. Before we go over the paper, I would like to thank Ian Peake for the brilliant app and adding in some of the "extra perks" such as the ECG recording. Fatmaxxer has stood the test of time and continues to lead the "pack" as far as I'm concerned. Lastly, many thanks to Juan and Pablo for the data access, advice and guidance. It's been an honor to work with this team.
Link to article ...
Some closing thoughts:
- Fatmaxxer a1 results will generally be quite close to Kubios under most circumstances. Where Kubios has an advantage is in cases of high artifact load, where the "automatic" correction method is superior.
- HRVT delineation will also be very well aligned and usually match Kubios within 1-2 bpm.
- However, excellent alignment and agreement are not the same as "identical". If one is interested in using a1 in exercise related research, Kubios is still the established standard. Yes, many original papers were done using their own "home grown" DFA a1 calculations. But, to maintain consistency with the current list of references, continued usage of Kubios HRV should be done.
- Other web and app based programs exist, and I've evaluated each with my own data. However, single case observations for a1 validation are not the same as what we have done in the present study. I would encourage other groups or even the app developers to perform the same type of analysis done here for assurance of Kubios similarity.
- Why is it important to reproduce Kubios methodology? Since we have certain a1 "anchor" points that correspond to thresholds (a1=0.5 for the LT2 or MMSS for example), non-Kubios calculation methods may yield markedly different values, leading to erroneous training targets. In addition, if a detrending method does not remove the non-HRV trends (e.g., baseline wander), the a1 may be falsely elevated, leading to failure to recognize autonomic destabilization.
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