Effects of aquatic exercise on pain, physical function, walking ability, and balance in older adults with knee osteoarthritis: a systematic review and meta-analysis

Objective Aquatic exercise is a low-impact option for older adults with knee osteoarthritis, but its effects across key clinical and functional outcomes and the influence of exercise prescription characteristics remain unclear. This study evaluated the effects of aquatic exercise on pain, physical function, walking ability, and balance and explored potential moderators of treatment effects. Methods PubMed, EBSCOhost, the Cochrane Library, Web of Science, and Embase were searched from inception to June 15, 2026. Randomized controlled trials comparing aquatic exercise with non-exercise or low-intensity control conditions in older adults with knee osteoarthritis were included. Risk of bias was assessed using Cochrane Risk of Bias 2, and certainty of evidence using GRADE. Small-sample–corrected standardized mean differences (SMDs) with 95% confidence intervals (CIs) were pooled using random-effects models with restricted maximum likelihood. Subgroup and leave-one-out sensitivity analyses were performed. Results Nine randomized controlled trials involving 499 participants were included. Aquatic exercise reduced pain (SMD = 0.91, 95% CI 0.21–1.60; I² = 88.1%) and improved physical function (SMD = 0.70, 95% CI 0.20–1.20; I² = 86.5%). Balance also improved (SMD = 0.93, 95% CI 0.54–1.32; I² = 57.7%), although only two studies contributed to this outcome. The effect on walking ability was not statistically significant (SMD = 0.44, 95% CI −0.75 to 1.62; I² = 95.0%). No statistically significant evidence of effect modification by exercise type, intervention duration, weekly frequency, or session duration was detected for pain or physical function (all P > 0.05). Certainty of evidence was low for pain, physical function, and balance and very low for walking ability. Conclusions Aquatic exercise may reduce pain and improve physical function in older adults with knee osteoarthritis and may have potential benefits for balance, although this finding is based on limited evidence. Its effect on walking ability remains uncertain, and current evidence does not identify an optimal aquatic exercise prescription. Given the low certainty of evidence for pain, physical function, and balance and the very low certainty for walking ability, these findings should be interpreted cautiously.