Three-time-point directional patterns of frailty and physical function in older adults participating in community gathering places in Koshigaya City, Japan: a retrospective exploratory study

Objective Community gathering places (Kayoinoba) promote social participation and may help prevent frailty among older adults. This exploratory study examined three-time-point trajectories of frailty and physical function and whether baseline multidimensional information helped distinguish favorable long-term trajectories. Methods This retrospective longitudinal study used municipal assessment data from Kayoinoba sites in Koshigaya City, Japan, collected at baseline (September 2016–October 2019), approximately 6 months later (March 2017–October 2020), and at the fiscal year 2022 municipal evaluation, conducted between August 2022 and November 2023. Outcome-specific samples included Kihon Checklist (KCL) total score ( n = 95), Timed Up and Go (TUG) test ( n = 74), one-leg standing time (OLS; n = 103), and 30 s Chair-Stand Test (CS-30; n = 100). Participants were classified into five prespecified direction-based trajectory patterns. Results Outcomes showed heterogeneous longitudinal patterns. CS-30 had the highest LongGood (51.00%) and ImproveMaintain (38.00%) rates. TUG had the lowest LongGood rate (27.03%) and frequent ImproveRebound (37.84%) and ConsistentDecline (28.38%) patterns. Domain-score models showed numerically higher apparent areas under the receiver operating characteristic curve for several outcomes, but optimism-corrected estimates were attenuated. Conclusions Frailty and physical function showed heterogeneous, outcome-dependent directional patterns. Findings are descriptive and hypothesis-generating, not causal evidence of Kayoinoba effectiveness.