Although the prevalence of chronic disability in older individuals remains on the decline in the United States, the total number of individuals over the age of 65 with chronic disability is increasing (1, 2). Presently, limitations in mobility affect almost one in four individuals over age 65 and three quarters of those living in nursing homes (3). In non-disabled older individuals, limitations in mobility in such tasks as climbing stairs, and walking across a room have been defined as "mobility disability" (4). To capture and assess mobility limitations in the elderly, performance tests of functional capacity have been developed and have been shown to be predictive of incident disability, institutionalization, and mortality (4, 5). In particular, walking ability alone, as measured by gait speed during a 4 M walk test, has been shown to be a strong predictor of subsequent ADL disability and mobility disability (6). In addition, validated highly reliable instruments to assess components of physical disability have also been developed and implemented in observational studies and clinical trials. More recently, testing protocols in selected animal models (rats, mice) have been developed to assess important endpoints related to impairments and functional limitations in these species.