Although frailty has been extensively investigated for the last 2 decades, preclinical models of frailty have only been developed over the past decade. Frailty is a concept that helps to explain the difference between chronologic age and biologic age and to discuss health span along with lifespan. In general, a frail individual will be more susceptible to adverse health outcomes than a healthy, nonfrail individual of the same age. However, the biology and mechanisms of frailty are still

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... The development of preclinical models of frailty and frailty assessment tools are invaluable to geriatric research. This review briefly describes the concept of frailty and discusses the newly developed animal models of frailty, specifically the frailty phenotype- and frailty index-based models. Mouse models are the most common models for preclinical frailty research, but rat and canine models for frailty assessment have also been developed. These models can facilitate the testing of frailty-specific treatments and help to investigate the effects of various interventions on frailty. Similarities and differences between human and animal models, including sex differences in frailty, are also discussed. The availability of animal models of frailty is a valuable and welcome addition to the study of frailty, aging, or the disorders of old age and will enable a better understanding of frailty mechanisms.