Optimal dose of aquatic exercise for improving muscle strength in older adults: a Bayesian model-based meta-analysis

Abstract

Objective: Amid global population aging, the progressive loss of muscle strength is a critical challenge compromising the functional independence of older adults. This study aimed to systematically quantify the dose–response relationship between various doses of aquatic exercise (frequency, session duration, total weekly duration, period, and intensity) and muscle strength in healthy older adults through a Bayesian model-based meta-analysis, in order to identify the optimal exercise protocol and inform precision exercise prescription. Methods: PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Infrastructure (CNKI), and Wan Fang Data were systematically searched for RCTs on aquatic exercise and older adults’ muscle strength up to March 2025. A conventional meta-analysis evaluated overall effects, followed by a Bayesian model-based dose–response meta-analysis using cubic restricted splines to quantify non-linear relationships. Standardized mean difference (SMD, with 95% CI/CrI) served as the effect measure. Results: A total of 13 RCTs (n = 531) were included. Overall, aquatic exercise significantly improved muscle strength (SMD = 0.56, 95% CI: 0.39–0.74, p < 0.0001). Dose–response analysis revealed cumulative trends for intervention period (peaking at 24 weeks, SMD = 0.65), frequency (2–3 sessions/week for significant gains), and total weekly duration (plateauing after 200 min, with significant effect at 100 min, SMD = 0.58). Conversely, session duration (optimal 30–45 min, peaking at 40 min, SMD = 0.62) and intensity (optimal Borg RPE 10–12, SMD = 0.45) showed inverted U-shaped relationships. Conclusion: Aquatic exercise is an effective strategy for improving muscle strength in healthy older adults, with its benefits demonstrating significant non-linear dose–response relationships. To maximize efficacy, the optimal recommended protocol consists of 2–3 sessions per week, each lasting approximately 40 min, at a moderate-to-high intensity (Borg RPE 10–12), and should be adopted as a long-term strategy. However, substantial heterogeneity and evidence of publication bias suggest cautious interpretation of pooled effects. Systematic review registration: Identifier: CRD420250654651.