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.

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.