Reducing sitting time is essential for preserving sarcopenia and functional independence with aging: a comparative cross-sectional study

Background As individuals age, sitting time is increasingly recognized as a factor that undermines independence in daily living; however, the extent to which sitting time influences sarcopenia-related indicators and functional independence remains unclear. Methods A total of 200 community-dwelling older adults aged 65–96 years were categorized into three groups based on daily sitting duration: low (<6 h/day), moderate (6–8 h/day), and high (>8 h/day) groups. Sarcopenic measures—including calf circumference, grip strength, 5-time chair stand test, and appendicular skeletal muscle mass (ASM)—were evaluated. Functional independence was examined using assessments of activities of daily living (ADL) and instrumental activities of daily living (IADL). Analysis of covariance (ANCOVA) was used to examine group differences across sitting time categories with adjustment for age and sex. Spearman’s correlation analysis was performed to examine associations between sitting time and sarcopenia-related indicators and functional independence variables, and separate simple linear regression were subsequently constructed with sitting time entered as the independent variable and sarcopenia-related indicators and functional independence variables included as dependent variables. Results Calf girth differed significantly by sex (η 2 = 0.995) and group (η 2 = 0.362). Grip strength showed a significant sex-by-group interaction (η 2 = 0.068), with a similar pattern observed for 5-time chair standing (η 2 = 0.069). ASM was primarily influenced by age (η 2 = 0.160), with no significant group or sex effects. Increasing sitting time was associated with greater functional decline in mobility-related ADL items, remaining significant after adjustment for age (η 2 = 0.077) and sex (η 2 = 0.286). Higher sitting time was also linked to poorer higher-level IADL functions (telephone use, housekeeping, transportation, and financial management), independent of age (η 2 = 0.023) and sex (η 2 = 0.243). ADL and IADL were strongly correlated (ρ = 0.812) and were significantly associated with sarcopenic indicators, including calf girth, grip strength, chair stand performance, and ASM. In regression analysis, sitting time was negatively associated with ASM (β = −0.415, p < 0.001), calf circumference (β = −0.442, p < 0.001), and grip strength (β = −0.385, p < 0.001), and positively associated with 5-time chair standing test (β = 0.465, p < 0.001), indicating poorer lower-extremity physical performance. In addition, sitting time was negatively associated with ADL sum score (β = −0.308, p < 0.001) and IADL sum score (β = −0.410, p < 0.001). Conclusion These findings suggest that longer sitting time may be broadly related to sarcopenia-related indicators and daily functional independence. However, because this study employed a cross-sectional design, these relationships should be interpreted as associations rather than causal effects.