Effects of polyphenol-rich interventions on the time-course of muscle recovery and athletic performance following exercise-induced muscle damage: a three-level meta-analysis

Abstract

Background Polyphenol-rich interventions are widely used to support recovery after exercise-induced muscle damage (EIMD), but their effects across outcome domains and recovery periods remain uncertain. Methods Seven databases were searched from inception to 14 August 2026 for randomized controlled trials in healthy adults. The primary analysis was restricted to unadjusted post-exercise endpoint values. Three-level meta-analytic models with structured variance-covariance matrices and CR2 cluster-robust inference were used to account for dependent effects. Parallel trials were analyzed using Hedges' g and crossover trials using SMCRP. Results Twenty-four randomized controlled trials contributed 195 primary effect sizes. Polyphenol supplementation was associated with a small improvement in pain/soreness (g = 0.252, 95% CI 0.049–0.454; p = 0.018). Effects on muscle-damage biomarkers (g = 0.097, 95% CI −0.249 to 0.442; p = 0.555) and performance (g = 0.238, 95% CI −0.017 to 0.493; p = 0.065) remained uncertain. The perceptual domain was represented by one study and was descriptive only. No statistically detectable differences were identified across prespecified recovery windows (HTZ p = 0.480) or supplementation strategies (HTZ p = 0.129). Certainty of evidence was low for muscle damage and performance and very low for pain/soreness and perceptual outcomes. Conclusion Polyphenol supplementation may modestly reduce post-exercise pain/soreness, but current evidence does not establish consistent improvements in objective recovery, an optimal recovery window, or superiority of any supplementation strategy. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/view/CRD420261449278, identifier: CRD420261449278.