RR Interval Recovery Dynamics Reflect Metabolic Load During Incremental Exercise

Oliver Jaroš1, Lukas Smital2, Tobiáš Goldschmidt1, Pavel Korvas3
1Department of Biomedical Engineering, Faculty of Electrical Engineering and Communication, Brno University of Technology, 2Brno University of Technology, Faculty of Electrical Engineering and Communication, Department of Biomedical Engineering, 3Center of Sports Activities, Brno University of Technology, Brno, Czech Republic

Abstract

Heart rate variability (HRV) is widely used to assess autonomic regulation, but its application to short, non-stationary recovery periods remains limited. In incremental lactate testing, brief recovery pauses provide an opportunity to analyze recovery dynamics under increasing metabolic load.

This study investigated the association between blood lactate concentration and RR interval-derived recovery dynamics during short recovery periods. Twelve physically active participants performed stepwise incremental tests on a cycle ergometer. RR intervals were recorded using a chest-strap sensor, and recovery segments were defined based on 1-min lactate sampling pauses. The primary feature was the RR slope during the first 30 s of recovery. Associations were assessed using correlation analysis and linear mixed-effects models.

RR slope showed the strongest association with lactate (Spearman rho = -0.79, p < 0.001), outperforming HRR30s and conventional HRV metrics, and remained significant in mixed-effects modeling (beta = -0.328, p < 0.001) and within-subject analysis.

These findings suggest that early RR-derived recovery dynamics provide a descriptor of metabolic load during incremental exercise and may complement HRV-based recovery assessment in short, non-stationary segments.