The aim of this study was to investigate the effectiveness of aquatic exercise in improving lower limb strength in people with musculoskeletal conditions. A systematic search utilized five databases including MEDLINE, Cumulative Index to Nursing and Allied Health Literature, Embase, SPORTdiscus and The Cochrane Library. Randomized controlled trials evaluating aquatic exercise with a resistance training component for adults with musculoskeletal conditions compared with no intervention or land-based exercise were identified. 15 studies from the initial yield of 1214 met these criteria. 9 of the 15 studies were of high quality, scoring at least six on the Physiotherapy Evidence Database Scale. Limited consideration of the prescription of resistance in the aquatic exercise and application of resistance training principles existed. Low or very low quality evidence indicates there was no difference in average effect between aquatic exercise and no exercise in improving hip abductor strength (SMD 0.28; 95%CI -0.04,0.59), knee extensor strength (SMD 0.18; 95%CI -0.03,0.40), knee flexor strength (SMD 0.13; 95%CI -0.20,0.45) or lower limb endurance (SMD 0.35; 95%CI -0.06,0.77). Low quality evidence indicates no difference in average effect between aquatic and land exercise for knee extensor (SMD -0.24; 95%CI -0.49,0.02) or flexor strength (SMD -0.15 ; 95%CI -0.53, 0.22).
It is likely that the inadequate application of resistance in water is a significant contributor to the limited effectiveness of aquatic exercise interventions in improving hip and knee muscle strength in people with musculoskeletal conditions. Future research is needed to quantify resistance with aquatic exercises and to determine if utilizing opportunities for greater resistance in aquatic rehabilitation as well as appropriate resistance training principles can be more effective in improving muscle strength.