Frailty
A clinical state, not a synonym for being old. It has criteria, it is measurable, and unusually for geriatrics it is partly reversible.
goodWell supported, with the usual caveats about effect size.Revised 21 Aug 2026
The defining feature is reserve: how badly a small insult goes.Photograph: Ravi Patel / Unsplash
Definition
A state of reduced physiological reserve across multiple systems, in which a minor stressor — a urinary infection, a new medication, two days in bed — produces a disproportionate and often lasting loss of function.
The word gets used loosely to mean “old and thin”. Clinically it is neither: a person can be eighty and not frail, or sixty-five and frail, and body size is not the criterion.
How it is identified
Two families of definition are in use.
The phenotype model treats frailty as a syndrome present when several of these co-occur: unintentional weight loss, self-reported exhaustion, weakness (usually grip strength), slow walking speed, and low physical activity. Three or more is conventionally frail; one or two is pre-frail.
The deficit-accumulation model counts a long list of symptoms, diseases and disabilities and expresses frailty as the proportion present — a frailty index. It behaves more like a continuous variable and predicts outcomes at least as well.
Neither is “correct”. They identify overlapping but not identical people, which is worth knowing when reading prevalence figures.
Why it matters more than a diagnosis list
Frailty predicts what the diagnosis list does not: how someone will come out of surgery, whether a hospital admission ends in a return home, how a new drug will be tolerated, and how a fall will go. It is increasingly used to decide the intensity of treatment, because chronological age is a poor guide and frailty is a better one.
The reversible part
This is the entry’s most useful content. Pre-frailty and mild frailty respond to intervention, and the components with evidence are unsurprising:
- Progressive resistance training, which addresses weakness and slowness directly.
- Adequate protein and energy intake, which addresses the weight loss and supports the training.
- Medication review, because polypharmacy contributes and deprescribing is an intervention.
- Treating the treatable — vision, hearing, depression, pain, and anything limiting mobility.
Multicomponent programmes combining these outperform any single one, which is consistent with frailty being a multi-system problem rather than a muscle problem.
Open questions
Whether frailty can be prevented decades earlier, rather than slowed once identified, is untested for the obvious reason: the trial would run for thirty years. The inference that building reserve in midlife raises the floor is plausible, widely repeated, and not directly demonstrated.