Supplementary Material for: Effect of Tai Chi and Qigong on Heart Rate Variability: A Systematic Review and Meta-Analysis Examining Baseline Autonomic Function and Intervention Complexity as Moderators in Adults

Introduction
Tai Chi and Qigong (TCQ) are mind–body practices widely recognized for their psychological benefits; however, the underlying physiological mechanisms remain less clearly defined. Time-domain heart rate variability (HRV) indices, specifically standard deviation of normal-to-normal intervals (SDNN) and root mean square of successive differences (RMSSD), serve as valuable markers of autonomic function. This meta-analysis quantified the effects of TCQ on these HRV parameters and examined whether baseline autonomic function and intervention complexity influenced outcomes.
Methods
Following PRISMA 2020 guidelines and a registered protocol (PROSPERO CRD420251053398), randomized controlled and quasi-experimental studies comparing Tai Chi and Qigong (TCQ) with control interventions in adults were systematically synthesized. Comprehensive searches were conducted in PubMed, Scopus, CINAHL Ultimate, and MEDLINE Ultimate databases from 2022 to 2025, with earlier studies identified through backward citation tracking. Eligible studies reported time-domain heart rate variability (HRV) outcomes with SDNN and RMSSD as the primary endpoints. The risk of bias was assessed using RoB 2 for randomized controlled trials and ROBINS-I for non-randomized studies. Random-effects meta-analyses were conducted to estimate Hedges’ g with 95% confidence intervals. Pre-specified moderators included baseline autonomic function and intervention complexity.
Results
Fifteen studies met the inclusion criteria, all involving participants who were naïve to Tai Chi and Qigong (TCQ). Ten studies (N = 543) provided SDNN data, and pooled analyses showed a moderate improvement with TCQ (g = 0.47, 95% CI [0.22, 0.72]; p < 0.001; I² = 49%; τ² = 0.078). Four studies (N = 212) reported RMSSD data, revealing a significant increase (g = 0.60, 95% CI [0.21, 0.99]; p = 0.002; I² = 49%; τ² = 0.078). The risk of bias was generally assessed as having some concerns. Notably, baseline autonomic function significantly moderated treatment effects, with larger gains observed in participants exhibiting preserved baseline autonomic function (Q = 7.59, p = 0.014); however, intervention complexity did not significantly influence outcomes (Q = 0.02, p = 0.89).
Conclusion
TCQ was associated with moderate improvements in time-domain HRV (SDNN and RMSSD). The effects were larger at normal baseline HRV, and we found no evidence that intervention complexity modified the outcomes. The certainty of evidence is limited by the risk of bias, potential confounding, and heterogeneity. Low-complexity readiness-tailored routines may be appropriate for pilot prevention or adjunctive programs. Confirmation requires well-powered baseline-stratified trials, particularly in impaired cohorts.