biostudies-literatureUnknown13Pleguezuelos E<h4>Background</h4>Post-coronavirus disease 2019 (post-COVID-19) syndrome is associated with persistent impairments in physical fitness and altered body composition, particularly in older adults. The extracellular-to-total body water (ECW/TBW) ratio has been linked to poor outcomes in clinical populations. However, its association with cardiorespiratory fitness (CRF) and muscular fitness (MF) in older adults with post-COVID-19 syndrome remains unclear. This study aimed to examine the associations between ECW/TBW ratio, CRF, MF, and other variables in this population.<h4>Methods</h4>A cross-sectional study was conducted in 71 older adults with post-COVID-19 syndrome. Hydration status and body composition were assessed using bioelectrical impedance analysis (BIA). CRF was evaluated by cardioFrontiers in nutrition1715783https://www.ebi.ac.uk/biostudies/studies/S-EPMC12932222biostudies-literatureExtracellular-to-total body water ratio is associated with comorbidity and cardiorespiratory fitness in older adults with post-COVID-19 syndrome.PMC12932222Sanchez-Nuno SBiurrun-Garrido AMoreno ESerra-Prat MMolina-Raya LGirabent Farres MGarnacho-Castano MVDel Carmen APleguezuelos EJerez-Molina CVinals XSerra-Paya NCastizo-Olier JfalseExtracellular-to-total body water ratio is associated with comorbidity and cardiorespiratory fitness in older adults with post-COVID-19 syndrome.<h4>Background</h4>Post-coronavirus disease 2019 (post-COVID-19) syndrome is associated with persistent impairments in physical fitness and altered body composition, particularly in older adults. The extracellular-to-total body water (ECW/TBW) ratio has been linked to poor outcomes in clinical populations. However, its association with cardiorespiratory fitness (CRF) and muscular fitness (MF) in older adults with post-COVID-19 syndrome remains unclear. This study aimed to examine the associations between ECW/TBW ratio, CRF, MF, and other variables in this population.<h4>Methods</h4>A cross-sectional study was conducted in 71 older adults with post-COVID-19 syndrome. Hydration status and body composition were assessed using bioelectrical impedance analysis (BIA). CRF was evaluated by cardio2026-01-01T00:00:00Z20262026-07-16T22:29:20.999Z2026-07-11T03:12:14.918ZS-EPMC129322224175662610.3389/fnut.2026.1715783