Heart Rate Variability During Prolonged Endurance Exercise: Implications for Durability: systematic review

Heart rate variability (HRV) is widely studied as a noninvasive indicator of autonomic cardiac regulation, exercise intensity, and fatigue during endurance exercise. Recently, the concept of “resilience”—defined as the ability to maintain physiological parameters and performance during prolonged exercise—has emerged as an important factor influencing endurance performance. Despite growing interest in endurance capacity, the contribution of cardiac autonomic regulation to this phenomenon remains poorly understood. Although numerous studies have examined HRV responses during prolonged endurance exercise, their findings have not yet been systematically synthesized in relation to the concept of endurance capacity. The aim of this systematic review is to capture changes in HRV during prolonged endurance performance and to link the areas of durability and autonomic nervous system regulation. Research question: How does heart rate variability change during prolonged endurance exercise, and what are the implications of these changes for the concept of durability? A systematic synthesis of the available evidence is therefore needed to provide a comprehensive overview of current knowledge, identify the methodological approaches used in the literature, evaluate the existing evidence, and highlight gaps requiring further research. This systematic review will follow the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020). Electronic searches will be conducted in the PubMed, Scopus, and Web of Science databases and SportDiscus using predefined search strategies. Eligible studies will include original, peer-reviewed research involving adult endurance athletes participating in prolonged endurance exercise under laboratory or field conditions. Studies examining changes in HRV during prolonged endurance exercise. The studies will be reviewed independently by two authors. PECO criteria P - Adult endurance athletes (recreational, trained, and elite) who engage in prolonged endurance exercise. E - Prolonged endurance exercise performed in laboratory or field settings during training sessions or endurance competitions in duration >60mins. C - Heart rate variability responses during or following prolonged endurance exercise and their potential relationship with autonomic regulation, fatigue, physiological drift and the concept of durability. O - HRV is changing. DFA a1 decrease with maintainning intensity Keywords: ("endurance athlete*" OR "endurance athletes" OR "trained athlete*" OR "well-trained athlete*" OR "competitive athlete*" OR "elite athlete*" OR "professional athlete*" OR "distance runner*" OR "marathon runner*" OR "ultramarathon runner*" OR "trail runner*" OR "cyclist*" OR "triathlete*" OR "cross-country skier*" OR "rower*" OR “cycling*“) AND ("heart rate variability" OR "heart-rate variability" OR HRV OR "cardiac autonomic regulation" OR "autonomic regulation" OR "autonomic nervous system" OR "cardiac autonomic function" OR "autonomic function" OR "DFA alpha1" OR "DFA-alpha1" OR "DFA a1" OR "DFA α1" OR "detrended fluctuation analysis alpha1" OR “RMSSD*“ OR “SDNN*“ OR “SD1*“ OR “SD2*“ OR “pNN50*“ OR "nonlinear heart rate variability" OR "fractal heart rate variability") AND (durability OR fatigability OR fatigue OR "exercise-induced fatigue" OR "physiological fatigue" OR "prolonged exercise" OR "prolonged endurance exercise" OR "prolonged running" OR "prolonged cycling" OR "exercise duration" OR "physiological drift" OR "cardiovascular drift" OR "heart rate drift" OR "cardiac drift" OR “bicycle ergometer“ OR “treadmill*“) Anticipated start date: 30.7.2026 Expected completion date: 31.10.2026 Data charting: data extraction form will be designed to capture all relevant study data and information addressing the pre-specified research questions. Data presentation: We will provide a systematic syntesis of our findings, using tables and charts where helpful.