9. What is intrinsic capacity, and why does it matter for aging?

Intrinsic capacity is the composite of an individual’s physical and mental capacities that provides the reserve to maintain or rapidly regain function after stress. Resilience describes recovery after a perturbation. iIt is related to intrinsic capacity but is not synonymous with it. In the WHO framework it includes five domains - locomotion, cognition, psychological function, vitality, and sensory function - and, together with the environment, determines functional ability. It captures aging at the system level, often earlier than disease, but later than molecular damage, and can serve as a practical target for measuring aging, and an endpoint for interventions aimed at preserving healthspan.