Your research can change the world
More on impact ›


Front. Sports Act. Living | doi: 10.3389/fspor.2021.668812

Real-time estimation of aerobic threshold and exercise intensity distribution using fractal correlation properties of heart rate variability: A single-case field application in a former Olympic triathlete Provisionally accepted The final, formatted version of the article will be published soon. Notify me

  • 1Medical School Hamburg, Germany
  • 2Independent researcher, Netherlands
  • 3Vrije Universiteit Amsterdam, Netherlands
  • 4Université Bourgogne Franche-Comté, France
  • 5Julius Maximilian University of Würzburg, Germany
  • 6University of Central Florida, United States

A non-linear heart rate variability (HRV) index based on fractal correlation properties called alpha1 of Detrended Fluctuation Analysis (DFA-alpha1), has been shown to change with endurance exercise intensity, crossing a value of 0.75 at the aerobic threshold (AT) in a population of recreational runners. Its unique advantage is that it provides information about current absolute exercise intensity without prior calibration to conventional lactate or gas exchange testing. A real-time estimation of this metric has several significant advantages. These include near instantaneous assessment of the AT during an exercise ramp or constant power intervals as well as information about time spent above the AT. Until of late no mobile based product could display DFA-alpha1 in real-time using off the shelf consumer products. However, an app designed for iOS devices, HRV Logger, was recently revised to display DFA-alpha1 from commonly used heart rate monitors. This brief research report illustrates the potential merits of immediate knowledge of this metric for the purposes of aerobic threshold determination as well as exercise intensity distribution at the zone 1 to 2 transition in a former Olympic triathlete. Three scenarios are presented, 1) calculation of a HRV threshold (HRVT) as a proxy for AT using Kubios HRV software via a typical cycling ramp, 2) determination of the HRVT during real-time monitoring using a cycling stage test, 3) a simulated training ride with enforcement of low intensity boundaries and real-time HRVT confirmation. To assist those interested in implementation, recommendations for the practical application will be given.

Keywords: HRV, autonomic nervous system, endurance exercise, Endurance training, polarized training

Received: 18 Feb 2021; Accepted: 04 May 2021.

Copyright: © 2021 Gronwald, Berk, Altini, Mourot, Hoos and Rogers. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Thomas Gronwald, Medical School Hamburg, Hamburg, Germany,