Assessment of Frailty in Animal Models

Animal models have contributed greatly to our understanding of the biology of aging and have been used to test new potential interventions to enhance survival. However, whether these interventions can modify frailty in animals is not yet clear, in part because until recently, frailty had not been considered in animal studies of aging. This review is focused on investigations that have attempted to address the issue of frailty, or aspects of frailty, in animal models, including invertebrate and vertebrate models. Some studies have used skeletal muscle weakness or sarcopenia as a surrogate for frailty in aging animals. Others have used genetically altered mice, in which components of human frailty such as inflammation are enhanced. This review also explores a novel approach to quantify frailty with a 'frailty index' based on deficit accumulation in aging animals. The concept of the frailty index is well established in the clinical literature, but recent work suggests that this approach can also be used to measure frailty in aging animals. The ability to quantify frailty in animals is a major step forward in the effort to understand the biology of frailty and to develop new clinical interventions.