Correlation Properties of Heart Rate Variability during a Marathon Race in Recreational Runners: Potential Biomarker of Complex Regulation during Endurance Exercise

Abstract

There is only very limited data examining cardiovascular responses in real-world endurance training/competition. The present study examines the influence of a marathon race on non-linear dynamics of heart rate (HR) variability (HRV). Eleven male recreational runners performed a self-paced marathon road race on an almost flat profile. During the race, heart rate and beat-to-beat (RR) intervals were recorded continuously. Besides HRV time-domain measurements, fractal correlation properties using short-term scaling exponent alpha1 of Detrended Fluctuation Analysis (DFA-alpha1) were calculated. The mean finishing time was 3:10:22 ± 0:17:56 h:min:s with a blood lactate concentration of 4.04 ± 1.12 mmol/L at the end of the race. Comparing the beginning to the end segment of the marathon race (Begin vs. End) significant increases could be found for km split time (p < .001, d = .934) and for HR (p = .010, d = .804). Significant decreases could be found for meanRR (p = .013, d = .798) and DFA-alpha1 (p = .003, d = 1.132). DFA-alpha1 showed an appropriate dynamic range throughout the race consisting of both uncorrelated and anti-correlated values. Lactate was consistent with sustained high intensity exercise when measured at the end of the event. Despite the runners slowing after halfway, DFA-alpha1 continued to fall to values seen in the highest intensity domain during incremental exercise testing in agreement with lactate assessment. Therefore, the discrepancy between the reduced running pace with that of the decline of DFA-alpha1, demonstrate the benefit of using this dimensionless HRV index as a biomarker of internal load during exercise over the course of a marathon race.

Concurrent Evolution of Biomechanical and Physiological Parameters With Running-Induced Acute Fatigue

“…However, those DFA-α 1 changes were mainly analyzed inlaboratory setting during incremental tests. Only one study reported a significant decrease of HR fractal properties during a marathon race (Gronwald et al, 2021). In our results, shortterm scaling exponents DFA-α 1 was not significantly lower at the end of the race compared to the baseline when all participants are combined (Table 1).…”

“…Acute fatigue can lead to a drop in the HRV metrics such as root mean square of successive differences between normal heartbeats (RMSSD) and the standard deviation of the heartbeat intervals (SDNN) when measured during exercise (Casties et al, 2006;Gronwald et al, 2020a). HRC variables such as the detrended fluctuation analysis (DFA-α1) coefficient, quantifying the degree of correlation of time series, respond to organismic demands during high intensity exercises (Hautala et al, 2003;Gronwald et al, 2021). Since running biomechanical parameters such as contact time, flight time, trunk flexion angle, vertical stiffness, ground reaction forces (GRF), etc.…”

“…This approach has an implicit assumption that different participants develop similar levels of fatigue at similar distances during the run, which may not be true for a heterogeneous participant group employing a variety of pacing strategies. Similarly, existing research on the continuous monitoring of heart rate dynamics and cardiac drift (Billat et al, 2019;Gronwald and Hoos, 2020;Gronwald et al, 2021) has generally considered their evolution over the distance of the run. Combined together, these studies investigate the neuromuscular and cardiovascular response to acute fatigue, but not their concurrent evolution and association.…”

On the distinct differences in autonomic regulation between pregnant and non-pregnant women - a heart rate variability analysis

“…However, recent studies have shown that α 1 is well-suited for capturing the fatigue of ultramarathon runners (Gronwald et al 2021, even in cases where HR remains steady (Rogers et al 2021) or when standard features such as SDNN and RMSSD show little relation to fatigue (Gronwald et al 2021). The researchers who performed this work suggest that during a fatigued state, the integration between the physiological subsystems of the human body over different timescales starts to break down, manifesting as the decoupling between systems (e.g.…”

Fractal correlation properties of heart rate variability as a marker of exercise intensity during incremental and constant-speed treadmill running

“…DFAα1 also responds to exercise training stress. For example, an attenuation of DFAα1 was observed after prolonged ultramarathon running (Rogers, Mourot, et al, 2021) and during a marathon, despite a reduction in running speed (Gronwald et al, 2021). Yet, DFAα1 has not been measured during constant-intensity exercise relative to physiological thresholds, and it is unknown whether DFAα1-derived thresholds determined from incremental exercise translate to constant-intensity exercise.…”