High-intensity interval training after stroke: a three-level random-effects meta-analysis with cluster-robust inference and exploratory dose-parameter signals.

Objective: To estimate the effects of high-intensity interval training (HIIT) on balance, walking outcomes, and physiological endpoints after stroke, and to generate hypotheses about whether training-load parameters may explain variability in intervention effects. Methods: We searched PubMed, Web of Science, Embase, Scopus, and the Cochrane Library from inception to December 31, 2025, for English-language randomized controlled trials of HIIT in post-stroke populations. Two reviewers independently screened records and extracted data. Risk of bias was assessed using RoB 2, and certainty of evidence was assessed using GRADE. Effect sizes were calculated as Hedges' g using between-group change scores. When change-score standard deviations were unavailable, they were imputed using a pre-post correlation of Results: Fourteen trials involving 717 participants were included. Pooled estimates suggested that HIIT may improve balance, as measured by the Berg Balance Scale, although the effect was small and the certainty of evidence was low ( Conclusions: Low- to very-low-certainty evidence suggests that HIIT may improve balance, walking endurance, and cardiorespiratory fitness after stroke, whereas effects on short-distance walking speed or gait control, blood pressure, and stroke severity remain uncertain. Apparent associations between training-load parameters and outcomes should not be interpreted as evidence of optimal HIIT prescriptions. These exploratory findings require confirmation in adequately powered randomized trials with standardized HIIT definitions, rigorous reporting of achieved intensity, and longer follow-up. Systematic review registration: https://www.crd.york.ac.uk/prospero/, identifier: CRD42027809778.