Acute effects of “exercise snacks” during prolonged sitting on hemodynamics and peripheral vascular function: a three-level meta-analysis

Prolonged sitting acutely impairs flow-mediated dilation (FMD) by reducing peripheral blood flow and vascular shear stress. Interspersing prolonged sitting with short bouts of physical activity (i. e. , “exercise snacks” or sedentary breaks) has been proposed as a strategy to mitigate these adverse effects. However, previous meta-analyses have been limited by small sample sizes and by inadequate handling of the statistical dependency arising from multiple effect sizes within studies, thereby limiting the robustness of their conclusions. We followed the PRISMA 2020 guidelines and registered the protocol with PROSPERO (CRD420261282295). We systematically searched PubMed, Web of Science, Embase, EBSCO, and the Cochrane Library (up to September 30, 2025) for randomized crossover or parallel controlled trials involving adults aged ≥ 18 years. Eligible studies compared the effects of sedentary breaks with prolonged sitting on acute hemodynamic and peripheral vascular outcomes. Data were pooled using a three-level random-effects model in R (metafor package) to account for statistical dependency, and the results were compared with those from traditional two-level models. We also reported 95% prediction intervals and conducted outlier diagnostics, leave-one-out sensitivity analyses, subgroup analyses, meta-regressions, and publication bias assessments. A total of 36 studies comprising 632 participants were included. Compared with prolonged sitting, sedentary breaks significantly improved flow-mediated dilation (Hedges’ g = 0. 44 95% CI, 0. 06–0. 81; P = 0. 02; GRADE: Moderate), increased peripheral blood flow (g = 0. 46 0. 22–0. 71; P < 0. 001; GRADE: Moderate), and reduced systolic blood pressure (MD = − 1. 67 mm Hg 95% CI, − 2. 81 to − 0. 52; P < 0. 001; GRADE: Moderate). Shear rate increased in the primary analysis (g = 0. 32 0. 09–0. 54; P = 0. 008; GRADE: Very Low) but became non-significant after trim-and-fill (\: R₀) adjustment, suggesting potential small-study effects. Moderator and meta-regression analyses indicated that shear rate improvements were influenced by the type of break (stair climbing yielded the largest effect) and were positively correlated with break duration. Improvements in peripheral blood flow were associated with the total duration of sitting. Among the additional hemodynamic and vascular outcomes, heart rate increased slightly (GRADE: Very Low), whereas mean arterial pressure (GRADE: Moderate), diastolic blood pressure (GRADE: Moderate), and peripheral arterial diameter (GRADE: Moderate) showed no significant consistent changes. Breaking up prolonged sitting with short bouts of physical activity (“exercise snacks”) acutely improves flow-mediated dilation and peripheral blood flow, and is associated with a small but statistically significant reduction in systolic blood pressure. Mean arterial pressure, diastolic blood pressure, and peripheral arterial diameter did not show consistent significant changes. Findings for shear rate and heart rate were sensitive to bias correction and should therefore be interpreted cautiously. Activity breaks involving large muscle groups (e. g. , stair climbing), performed for 2–5 min every 30–60 min, may be particularly beneficial for vascular protection. Where feasible, reducing total sedentary time and avoiding prolonged uninterrupted sitting may also be important.