Fractal Correlation Properties of Heart Rate Variability Differentiates Training Intensity During and After Energy-Matched Cycling Sessions.

Authors

Anton Olieslagers, Yoram Müller-Jabusch, Jens De Maeseneer, Maura Seynaeve, Toon T de Beukelaar

Published in

Medicine and science in sports and exercise. Sep 14, 2026. Epub Sep 14, 2026.

Abstract

Recovery optimization requires precise monitoring of physiological stress. This study examines whether detrended fluctuation analysis alpha 1 (DFAa1), a non-linear heart rate variability index, exhibits intensity-dependent responsiveness across energy-matched training sessions in cycling.
Nineteen endurance-trained male participants (18-35yrs) completed three equalized workload protocols at different intensities: light (LIGHT), moderate (MOD), and high-intensity interval training (HIIT). Training sessions were matched for energy expenditure by adjusting time via the formula E=P×Δt (E=Energy (J); P=power (W); Δt=time (s)). LIGHT and MOD training were conducted at first and second lactate threshold power (i.e. LT1 and LT2), respectively. HIIT followed a 10x1min protocol at 110% V̇O₂peak power, alternated with 1min rest at 80% LT1 power. Heart Rate (HR) and DFAa1 were assessed throughout the different intensity training sessions as well as during a standardized 10min warm-up (WU) and cool-down (CD) at LT1.
DFAa1 showed apparent stability during LIGHT (p=0.997) and MOD sessions (p=1.000), while showing deterioration during HIIT (p<0.001). On the other hand, HR drift was apparent for all intensities (LIGHT: p=0.003; MOD: p<0.001; HIIT: p<0.001). When directly comparing DFAa1 and HR via ΔZ-scores, a significant effect was found only in MOD (p=0.008). Interestingly, DFAa1 demonstrated significant WU to CD differences for MOD and HIIT (p<0.001), but not for LIGHT (p=0.210), while HR responses showed significant WU to CD differences for all intensities (p<0.001). ΔZ-scores showed significant differences between DFAa1 and HR in MOD (p=0.039) but no significant differences in LIGHT (p=0.098) and HIIT (p=0.071).
These findings seem to reinforce that DFAa1 holds promise as an objective, system-wide marker of internal workload across varying exercise domains.

PMID:
42735359
Bibliographic data and abstract were imported from PubMed on 15 Sep 2026.

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