Adopting a Complex Systems Approach to Functional Ageing: Bridging the Gap between Gerontological Theory and Empirical Research

Related to but distinct from biological and environmental systems, we define functional ageing as the interacting changes in physical and mental body functions, behavioural factors and social participation that occur as individuals age. We propose that a complex systems perspective to functional ageing can illuminate how outcomes such as quality of life and longevity, and prevention and treatment success emerge from dynamic interactions among these domains, rather than from single causes. We support this view in three ways. First, we explain how key principles of complex systems science – resilience, non-linearity and heterogeneity – apply to functional ageing. Second, we show how established gerontological theories and geriatric models align with these principles. Third, we illustrate the use of novel methodological tools from complex systems science in studying functional ageing. Finally, we offer a glossary of key concepts and recommendations for researchers to adopt this perspective in future studies on functional ageing.