Frailty, Physical Frailty, Sarcopenia: A New Conceptual Model

In the literature, different criteria have been validated to identify frail older subjects, which mainly refer to two conceptual models: the cumulative deficit approach proposed by Rockwood and the Physical Frailty (PF) phenotype proposed by Fried. Both models have received empirical validation. Nevertheless, the frailty phenotype is the most widely used and presents a characterized pathophysiologic background. The PF condition depicted by the frailty phenotype has shown to be predictive of major negative health-related outcomes, including mobility disability, disability for activities of daily living, institutionalization, and mortality. At the same time, it cannot be ignored that the PF phenotype presents substantial overlaps with sarcopenia, "a syndrome characterized by progressive and generalized loss of skeletal muscle mass and strength with a risk of adverse outcomes such as physical disability, poor quality of life and death". In fact, many of the adverse outcomes of frailty are probably mediated by sarcopenia. Therefore, sarcopenia may be considered both as the biological substrate for the development of PF and the pathway through which the negative health outcomes of frailty ensue. Although PF encompasses only a part of the frailty spectrum, the identification of a definite biological basis (i.e., skeletal muscle decline) opens new venues for the development of interventions to slow or reverse the progression of this condition. Here, we present a novel conceptualisation of PF which will possibly promote significant advancements over the traditional approaches to this syndrome by enabling the precise operationalisation of the condition, a clear identification of the affected population and the rapid translation of findings to the clinical arena.