Assessment of Bidirectional and Threshold-Response Associations Between Cognitive Function and Physical Performance: Nationwide Cross-Sectional Study

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Background: The global aging population faces increasing risks of cognitive and physical decline, yet the bidirectional and nonlinear dynamics between these domains remain poorly understood. Objective: This study aims to investigate the bidirectional and nonlinear associations between cognitive function and physical performance in older adults and to identify threshold effects and population subgroups at elevated risk. Methods: This multicenter study of 20,868 older adults in China analyzed the bidirectional asymmetric and threshold-response associations between cognitive and physical function using logistic or linear regression and restricted cubic spline, with subgroup and interaction analyses. Results: The study revealed an asymmetrical bidirectional relationship between cognitive function and physical performance, with cognitive impairment having a stronger association with physical function (Short Physical Performance Battery [SPPB], odds ratio [OR] 2.45, P<.05 vs 1.16,P=.051; gait speed: OR 2.36,P<.05 vs 1.89, P<.050). Restricted cubic spline analysis identified 3 key inflection points at Mini-Mental State Examination (MMSE) scores of 19, 24, and 29. When MMSE <24, cognitive improvement significantly protected physical performance (SPPB: OR 0.86, 95% CI 0.84-0.87; gait speed: OR 0.84, 95% CI 0.82-0.85). The critical intervention window was between MMSE 19-24 (SPPB, OR 0.66, 95% CI 0.57-0.77). At MMSE ≥24, balance protection remained significant (OR 0.69, 95% CI 0.68-0.70), but overall physical performance showed diminished effects, with SPPB demonstrating a weaker, marginal association (P=.051). A paradoxical reversal effect was observed for gait speed (OR 1.05, 95% CI 1.04-1.07). High-income (OR 5.24, 95% CI 3.91-7.02) and high-education subgroups (OR 3.98, 95% CI 1.48-10.70) exhibited heightened vulnerability. Conclusions: This study demonstrates a bidirectional, asymmetric relationship between cognitive function and physical performance, identifies a nonlinear threshold effect, and highlights population heterogeneity.

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