Association Between Cellular Hydration Patterns and Hydroelectrolytic Regulation with Muscle Strength in Older Adults

Introduction: Muscle function is influenced by hydroelectrolytic mechanisms that regulate cellular volume beyond isolated plasma electrolyte concentrations. However, the role of integrated hydration and electrolyte regulation profiles in muscle function among older adults remains insufficiently understood. Objective: To identify which physiological domains of hydroelectrolytic regulation are most strongly associated with muscle strength and functional performance in community-dwelling older adults. Methods: A cross-sectional study was conducted in 96 community-dwelling individuals aged ≥ 70 years. Markers of cellular hydration and membrane integrity were assessed using bioelectrical impedance analysis, together with first-morning fasting plasma and urinary sodium and chloride concentrations. Principal component analysis (PCA) was applied as a data-driven approach to identify latent domains of coordinated hydroelectrolytic regulation. Associations between component scores and handgrip strength and Timed Up and Go (TUG) were examined using two sequential multivariable regression models: Model 1 adjusted for sex and fat-free mass index (FFMI); Model 2 additionally adjusted for age, hypertension, and diuretic use. Results: Three principal components were retained, explaining 77.5% of total variance: PC1 (renal-cellular domain), PC2 (plasma electrolyte domain), and PC3 (cellular volume domain). For handgrip strength, Model 1 showed significant associations for PC3 (β = 0.152; p = 0.025) and PC1 (β = 0.180; p = 0.050). In Model 2, only PC3 remained independently associated (β = 0.146; p = 0.036). For TUG, Model 1 showed associations for PC1 (β = -0.262; p = 0.049) and PC3 (β = -0.238; p = 0.015). In Model 2, PC1 (β = -0.308; p = 0.019) and PC2 (β = -0.190; p = 0.046) remained independently associated, whereas PC3 was not. Conclusions: Maximal force production appears primarily associated with cellular volume regulation, whereas functional performance reflects broader multi-compartmental hydroelectrolytic integration involving renal and plasma domains. These findings suggest that multidimensional hydration profiling may complement isolated biochemical markers in the functional assessment of older adults, warranting validation in longitudinal studies.