Intracellular Water Content in Lean Mass is Associated with Muscle Strength, Functional Capacity, and Frailty in Community-Dwelling Elderly Individuals. A Cross-Sectional Study

High intracellular water (ICW) content has been associated with better functional performance and a lower frailty risk in elderly people. However, it is not clear if the protective effect of high ICW is due to greater muscle mass or better muscle quality and cell hydration. We aimed to assess the relationship between ICW content in lean mass (LM) and muscle strength, functional performance, frailty, and other clinical characteristics in elderly people. In an observational cross-sectional study of community-dwelling subjects aged ≥75 years, ICW and LM were estimated by bioelectrical impedance, and the ICW/LM ratio (mL/kg) calculated. Muscle strength was measured as hand grip, frailty status was assessed according to Fried criteria, and functional status was assessed by Barthel score. For 324 recruited subjects (mean age 80 years), mean (SD) ICW/LM ratio was 408 (29.3) mL/kg. The ICW/LM ratio was negatively correlated with age (r(s) = −0.249; p < 0.001). A higher ICW/LM ratio was associated with greater muscle strength, better functional capacity, and a lower frailty risk, even when adjusted by age, sex, nº of co-morbidities, and LM. ICW content in LM (including the muscle) may influence muscle strength, functional capacity and frailty. However, further studies are needed to confirm this hypothesis.