Study-level age patterns in cardiometabolic response to high-intensity interval training among adults with overweight or obesity: a systematic review and meta-analysis of randomized controlled trials.

BACKGROUND: HIIT is a time-efficient exercise strategy for adults with overweight or obesity, but trial findings are heterogeneous and whether age independently modifies cardiometabolic response remains uncertain. METHODS: PubMed, Embase, the Cochrane Library, and Web of Science were searched from inception to December 2025. Random-effects meta-analyses estimated weighted mean differences for SBP and DBP in mmHg and standardized mean differences for lipid and anthropometric outcomes, with 95% confidence intervals and prediction intervals where available. Additional Stata analyses included funnel plots, Egger tests for all six outcomes, trim-and-fill analysis for BW and BMI, exploratory study-level meta-regression using continuous mean age and intervention duration, and GRADE assessment. RESULTS: Nineteen trials involving 570 participants were included. HIIT was associated with reductions in SBP, DBP, TG, BW, and BMI and an increase in HDL-C; overall heterogeneity was moderate to substantial (I² range, 46.77%-87.07%). Egger tests suggested small-study effects for BW and BMI, but not SBP, DBP, HDL-C and TG. Trim-and-fill imputed no studies for BW and BMI. Mean age was associated with TG effects and duration was associated with HDL-C effects in univariable models. Certainty of evidence was low for SBP and very low for the remaining outcomes. CONCLUSION: HIIT was associated with favorable average cardiometabolic changes in adults with overweight or obesity, but substantial heterogeneity, low-to-very-low certainty and possible small-study effects findings require cautious interpretation. The available evidence supports the hypothesis that trial-level mean age may be associated with differential responses, rather than proving age as a definitive individual-level effect modifier. SYSTEMATIC REVIEW REGISTRATION: https://www.crd.york.ac.uk/prospero/, identifier CRD420261279689.