Heart rate-based indices to detect parasympathetic hyperactivity in functionally overreached athletes. A...

Area of Science:

• Exercise Physiology
• Sports Science
• Autonomic Nervous System

Background:

• Investigating parasympathetic nervous system (PNS) changes in functionally overreached (F-OR) endurance athletes using heart rate (HR)-derived indices has yielded inconsistent results.
• Methodological inconsistencies may contribute to the lack of clarity in previous research.
• Understanding PNS modulation is crucial for managing training loads and preventing overreaching in athletes.

Purpose of the Study:

• To systematically review and meta-analyze the sensitivity of resting and post-exercise vagal-related HR variability (HRV) and HR recovery (HRR) indices in detecting PNS modulation in F-OR and non-overreached (non-OR) athletes.
• To examine the impact of methodological factors on the sensitivity of HR-based indices for detecting PNS hyperactivity in F-OR athletes.

Main Methods:

• Systematic literature search of CENTRAL, Scopus, PubMed, Embase, and Web of Science up to May 2020.
• Inclusion of studies on endurance-trained athletes undergoing overload training, measuring PNS modulation via HR-based indices.
• Random-effects model meta-analysis to calculate standardized mean differences (SMD) based on fatigue status (F-OR vs. non-OR) and subgroup analyses for methodological factors.

Main Results:

• Resting vagal-related HRV indices did not significantly detect PNS hyperactivity in F-OR athletes (SMD = -0.01) nor show significant differences compared to non-OR athletes (SMD = 0.15).
• Subgroup analysis indicated a moderate increase in weekly averaged HRV in F-OR athletes (SMD = 0.81), though isolated HRV values lacked statistical significance (SMD = -0.45).
• HRR indices showed a moderate and significant increase in F-OR athletes (SMD = 0.65) compared to non-OR athletes (SMD = 0.10), with significant differences between groups (P < 0.001).

Conclusions:

• HRR indices are sensitive to increased PNS modulation in F-OR athletes, particularly when considering methodological factors.
• While resting vagal-related HRV indices showed limited sensitivity, weekly averaged HRV may be a more reliable indicator of PNS changes in F-OR athletes.
• Methodological considerations are crucial for accurately assessing PNS modulation and functional overreaching in endurance-trained athletes using HR-based measures.