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

Abstract

Investigations into the sensitivity of heart rate- (HR) derived indices for tracking parasympathetic nervous system (PNS) changes in functionally overreached (F- OR) endurance- trained athletes have produced equivocal findings. Lack of clarity may be a result of methodological inconsistencies. Therefore, the aims of this system atic review and meta- analysis were (a) to determine the sensitivity of resting and post- exercise vagal- related HR variability (HRV) and HR recovery (HRR) indices to detect PNS modulation in F- OR and non- overreached (non- OR) athletes, and (b) to investigate the influence of methodological factors on the sensitivity of HR- based in dices to detect PNS hyperactivity in F- OR athletes. We searched CENTRAL, Scopus, PubMed, Embase, and Web of Science up to May 2020 for the following terms: male and female endurance- trained athletes, controlled and uncontrolled studies that car ried out an overload training period, and PNS modulation measured in resting and post- exercise, pre- and post- overload training period. A random- effects model of standardized mean difference (SMD) was estimated for each outcome measure based on the training- induced fatigue status (F- OR vs non- OR athletes), and the influence of methodological issues to detect PNS hyperactivity in F- OR was assessed by sub group analyses. Pooled analysis showed that resting vagal- related HRV indices did not detect PNS hyperactivity in F- OR athletes (SMD+ = −0.01; 95% confidence in terval [CI] = −0.51, 0.50), and no statistical difference (P = .600) was found with non- OR athletes (SMD+ = 0.15; 95% CI = −0.14, 0.45). However, subgroup analysis based on HRV parameter showed a moderate statistical increase in weekly averaged HRV in F- OR athletes (SMD+ = 0.81; 95% CI = 0.35, 1.26), while isolated HRV values did not reach statistical significance (SMD+ = −0.45; 95% CI = −0.96, 0.06). We observed a moderate and statistically significant increase in HRR indices among F- OR athletes (SMD+ = 0.65; 95% CI = 0.44, 0.87), no changes for non- OR ath letes (SMD+ = 0.10; 95% CI = −0.15, 0.34), and statistically significant differences between F- OR and non- OR athletes (P < .001). Insufficient data prevented meta- analysis for post- exercise vagal- related HRV indices. Our findings show that when methodological factors are considered, HR- based indices are sensitive to increased PNS modulation in F- OR.