Study Protocol of the 10-Year Longitudinal Amersfoort Cohort Study on Functional Decline, Healthy Aging, and Frailty (AMCOHF) in a Community-Dwelling Older Population.

Introduction: Frailty, characterized by a reduction in intrinsic capacity across multiple physiological systems, is a key concern in healthy aging. Insight in the trajectory of an individual's functional ability and intrinsic reserve capacity in a relatively younger population of older adults is lacking. This study aims to investigate the early stages of frailty by tracking trajectories of physical indicators of intrinsic capacity before frailty becomes clinically evident.

Methods: The AMersfoort COhort study on functional decline, Healthy aging and Frailty (AMCOHF) is a unique 10-year prospective cohort study evaluating the predictive value of longitudinal trajectories of physical parameters for frailty onset or robustness maintenance. An a-select community-dwelling robust population of Amersfoort (55-75 years) in the Netherlands will undergo baseline assessments for inclusion criteria and will be followed longitudinally every 2.5 years. Frailty status is assessed using the Fried phenotype, Rockwood frailty index, and Groningen frailty indicator. Testing procedures and questionnaire completion include physical performance tests in the domains: (1) musculoskeletal system, (2) articular system, (3) cardiorespiratory system, (4) sensory system, (5) immune system, and 6) uro-gynecological system. Study outcomes focus on intrinsic capacity, functional ability, explanatory data, and frailty. Statistical analyses evaluating the predictive capacity include logistic regression, confirmatory factor or latent class analysis, and structural equation modeling. Nonprobability convenience sampling recruits 2,078 robust participants, estimating a 1-year frailty incidence of 1.5%-6.0%. Ethical approval was obtained, and the trial is prospectively registered on Open Science Framework (DOI: 10.17605/OSF.IO/RMBQV).

Conclusion: The AMCOHF study will contribute to knowledge about markers to predict an accelerated decline in intrinsic capacity in an early stage. This knowledge is important to deploy prevention strategies at an earlier stage in life then those currently undertaken, ultimately reducing healthcare costs and contributing to a healthy aging population.