Objective Measures of Physical Functioning, Disabilities in Daily Life and Trends During Ageing: A Repeated Cross-Sectional Study.

BACKGROUND: Maintenance of adequate physical functioning is key for lifelong health, particularly for an ageing society with increasing health care needs. We aimed to assess the association of two objective physical function (PF) measures with functional capacity (FC) outcomes, while also exploring the underlying trends. METHODS: This was a repeated cross-sectional study. We used data from a nationally representative survey of middle-aged and older Chinese individuals across 150 counties or districts across 28 provinces of China. Longitudinal data from three waves collected in 2011 (baseline, n = 4753), 2013 (n = 4922) and 2015 (n = 6165) were used for parallel analysis. PF was measured using the five-time chair stand test (CST) and gait speed (GS). FC outcomes were assessed using 20 items related to activities of daily living or instrumental activities of daily living. We conducted various analyses, including dose-dependent analyses, cutoff development, multivariate analyses and causal inference, to systematically examine the associations across multiple dimensions. RESULTS: A total of 15 840 participants from three waves were analysed. FC limitations increased as the study population aged. The most frequently reported limitation across all three waves was the inability to jog 1 km (59.2%, 60.3% and 60.7%, respectively). Compared to low GS, prolonged CST time was more strongly associated with a greater number of FC limitation items (2011, 20 vs. 16; 2013, 20 vs. 16; 2015, 20 vs. 20). The associations between both PF measures and outcomes were predominantly nonlinear and dose-dependent (all p < 0.05). Overall, CST showed superior performance relative to GS for diagnosing different FC limitations. The optimal global cutoffs were 0.66 m/s for GS and 10.85 s for CST. Controlling for age, sex and BMI, we noted that CST had generally higher standardized odds ratios than GS in predicting FC outcomes. Causal inference analysis revealed that CST had a stronger direct causal effect on overall FC than GS, both at the global and local levels in all three waves (for instance, average treatment effect in the baseline survey, CST = 0.729, 95% CI = 0.470-0.989, GS = 0.235, 95% CI = 0.033-0.438). CONCLUSIONS: PF measures have varied performance to reflect the diversity and magnitude of activities individuals actually perform. CST has stronger associations with multidimensional FC than GS despite the ageing process. This superiority also exists in those activities that do not primarily involve the lower limb musculoskeletal system. These findings are crucial for health stakeholders to develop more targeted strategies for managing functional limitations.