Different doses of aquatic exercise for improving muscle strength in older adults: a meta-analysis

Abstract

OBJECTIVE: To systematically evaluate and quantify the effects of different doses of aquatic exercise on muscle strength in healthy older adults using a Bayesian model-based dose-response meta-analysis, thereby determining the optimal exercise regimen and providing evidence-based recommendations for precise exercise prescription. METHODS: A systematic search was conducted in both English and Chinese databases, including PubMed, Embase, Web of Science, CNKI, and WanFang, to identify randomized controlled trials published up to March 2025 that investigated the effects of aquatic exercise on muscle strength in older adults. Data analysis was performed using R 4.5.0. A conventional meta-analysis was first conducted to estimate the overall effect, followed by a Bayesian model-based dose-response meta-analysis to quantify the nonlinear relationships between different exercise dose dimensions (frequency, session duration, weekly total duration, period, and intensity) and muscle strength improvement. The standardized mean difference (SMD) with 95% confidence interval (CI) was used as the effect size. RESULTS: A total of 13 randomized controlled trials involving 531 participants were included. The overall meta-analysis showed that aquatic exercise significantly improved muscle strength in older adults compared with control (SMD=0.56, 95%CI 0.39-0.74, P < 0.0001). Dose-response analysis revealed cumulative trends for training period, frequency, and weekly total duration: the effect peaked at 24 weeks (SMD=0.65, 95%CI 0.40-0.66); significant gains were achieved at a frequency of twice per week (SMD=0.56, 95%CI 0.22-0.58), with a slight increase at three times (SMD=0.62, 95%CI 0.24-0.62); weekly cumulative duration showed significant effects at 100 minutes (SMD=0.58, 95%CI 0.34-0.60) and plateaued after 200 minutes. In contrast, session duration and intensity exhibited an inverted U-shaped relationship: the effect peaked at 40 minutes per session (SMD=0.62, 95%CI 0.32-0.82), with an optimal range of 30-45 minutes; the optimal intensity was Borg RPE 10-12 (SMD=0.45, 95%CI 0.18-0.46), with diminishing returns beyond this range. CONCLUSION: Aquatic exercise is an effective strategy for improving muscle strength in healthy older adults. It is recommended that older adults engage in aquatic exercise two to three times per week, with each session lasting approximately 40 minutes, at a moderate-to-vigorous intensity (Borg RPE 10-12), and as a long-term strategy.

1. Introduction

Muscle strength decline can affect the health, independent living ability, and quality of life of the elderly population [1]. With aging, muscle strength deteriorates, affecting bone support and internal organ function [2], forming a vicious cycle of 'muscle loss → reduced activity → further muscle loss' [3]. Muscle mass decreases by 1%-2% per year in people over 60 years old [4], which is a major cause of muscle strength decline.

Among intervention strategies to counteract age-related physical decline, regular physical exercise as a non-pharmacological intervention has been well-validated by evidence-based medicine. Existing studies show that systematic exercise training can significantly improve multiple functional indicators in the elderly through dual mechanisms of neuromuscular adaptation and metabolic regulation, such as balance, agility, cardiorespiratory endurance, and muscle strength [5]. Aquatic exercise stands out as an effective strategy for improving muscle strength among various exercises [6-8]. As a low mechanical stress exercise mode, aquatic exercise is an effective low-impact workout for the elderly. The buoyancy of water significantly offsets body weight load, thereby reducing compressive stress on joints and muscles, lowering the risk of exercise, and improving health [9]. Due to the physical properties of water, its density is 800 times higher than air, and it has viscosity, so moving in water encounters greater resistance than on land, requiring more muscle strength and forcing muscle groups to produce greater concentric contractions [10]. Moreover, compared with land, water is also a safe place for low-intensity exercise [11], and even elderly individuals who are too frail to exercise safely and effectively on land may benefit. The more supportive and effective environment in water may also positively improve exercise adherence [12]. However, research results on changing muscle strength in the elderly through aquatic exercise remain controversial in the literature.

Multiple trials have confirmed that aquatic training can improve muscle strength in the elderly. High-intensity aquatic exercise programs can effectively enhance upper and lower limb strength in elderly women [13]. Evidence from several systematic reviews and meta-analyses indicates that aquatic exercise can improve muscle strength in both young and elderly individuals [14], lower blood pressure [15-16], and increase maximal oxygen uptake [17]. Using assistive devices during exercise to increase resistance and control resistance can yield maximal strength gains in the elderly [18]; however, in the same study, when training movements were not resistance-controlled, the maximal shoulder flexion strength did not significantly improve.