Background: Muscle strength is essential for maintaining functional capacity, particularly among aging populations, as it helps mitigate age-related declines in muscle mass. However, limited evidence exists regarding whether baseline characteristics - such as age, initial strength levels, body composition, and quality of life - or training program features like duration and intensity influence strength improvements following water aerobics. Aim: To investigate whether gains in muscle strength from a water aerobics program are associated with program intensity and duration, participant age, and baseline levels of strength, body composition, and quality of life. Methods: Data from two pragmatic randomized controlled trials were analyzed, comparing 12* and 24*week programs of moderate- versus high-intensity water aerobics in adult and older women. Forty-one women (66.20 ± 9.25 years) participated: 21 completed the 12*week program [moderate-intensity group (MIG), n=11; high-intensity group (HIG), n=10], and 20 completed the 24*week program (MIG, n=10; HIG, n=10). Assessments included muscular endurance, explosive strength, body mass index, fat mass, and general quality of life measured at baseline and post-intervention. Multiple linear regression analyses examined associations between training variables and strength outcomes. Results: Upper-limb explosive strength was influenced by baseline explosive strength, muscular endurance, and body mass index. Lower-limb explosive strength was associated with age and baseline levels of fat mass, quality of life, and lower-limb muscular endurance. Upper-limb muscular endurance was related to age and baseline lower-limb muscular endurance. Lower-limb muscular endurance was associated with training intensity and baseline lower-limb muscular endurance. Conclusions: Water aerobics intensity plays a significant role in enhancing lower-limb muscular endurance. Overall, improvements in strength derived from water aerobics appear predominantly influenced by participants` initial muscular endurance, body composition, and age. These factors should be carefully considered when designing and individualizing training programs.
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