Monitoring and adapting endurance training on the basis of heart rate variability monitored by wearable technologies: A systematic review with meta-analysis

Objectives: To systematically perform a meta-analysis of the scientific literature to determine whether the outcomes of endurance training based on heart rate variability (HRV) are more favorable than those of predefined training. Design: Systematic review and meta-analysis. Methods: PubMed andWeb of Science were searched systematically inMarch of 2020 using keywords related to endurance, the ANS, and training. To compare the outcomes of HRV-guided and predefined training, Hedges' g effect size and associated 95% confidence intervals were calculated. Results: A total of 8 studies (198 participants) were identified comprising 9 interventions involving a variety of approaches. Compared to predefined training, most HRV-guided interventions included fewer moderate- and/ or high-intensity training sessions. Fixed effects meta-analysis revealed a significant medium-sized positive effect of HRV-guided training on submaximal physiological parameters (g = 0.296, 95% CI 0.031 to 0.562, p = 0.028), but its effects on performance (g = 0.079, 95% CI - 0.050 to 0.393, p = 0.597) and (V)over dotO2peak (g = 0.171, 95% CI -0.213 to 0.371, p = 0.130) were small and not statistically significant. Moreover, with regards to performance, HRV-guided training was associated with fewer non-responders and more positive responders. Conclusions: In comparison to predefined training, HRV-guided endurance training had amedium-sized effect on submaximal physiological parameters, but only a small and non-significant influence on performance and (V)over dotO2(peak). There were fewer non-responders regarding performance with HRV-based training. (C) 2021 The Author(s). Published by Elsevier Ltd on behalf of Sports Medicine Australia.