Preserving late-life mobility, defined as the ability to walk safely and independently, is central to maintaining a high quality of life, is critical for the performance of many activities of daily living and is necessary for maintaining physical independence. Therefore, the continued development and standardization of tools that can reliably assess physical functioning and disability status will be important for addressing the growing challenge that societies worldwide will face with the expanding older population. The physical function assessment core seeks to continue to provide the necessary infrastructure to perform standardized, valid and reliable measures of musculoskeletal impairments, physical function, and disability across the spectrum of observational studies and clinical trials embedded within, supported by, or associated with the Boston-OIAC. The leadership of this core has collaborated extensively over the past sixteen years, has unique experience in the application of these measurements across a wide range of cross-sectional and intervention studies in older adults, and has been on the leading edge of the development and refinement of new instruments and technologies to assess domains of physical function and disability. We propose to examine the following specific aims: Aim 1: We will provide an organized infrastructure for FAC-supported procedures and activities across Tufts' Human Nutrition Research Center on Aging (Drs. Fielding and Reid), Boston University's Health and Disability Research Institute (HDRI) (Drs. Jette, Latham, and Beauchamp), and Brigham and Women's Hospital Laboratory of Exercise Physiology and Physical Function (Dr. Storer) and serve as focal point for interdisciplinary collaboration by OAIC investigators in the development, evaluation, and application of new and existing tools and instruments to assess musculoskeletal impairments, physical function, and disability in older adults to evaluate the efficacy of function promoting therapies. Aim 2: We will provide direct measurement and consultative services, as well as assist with proposal development for clinical studies supported by, or associated with, the theme of the OAIC that require measures of musculoskeletal impairments, physical function, and/or disability. All Core services will use standardized equipment and operating protocols for the assessment of muscle performance and functional limitations in human studies, and will maintain extensive quality control procedures. Aim 3: We will develop novel and innovative approaches to assess musculoskeletal impairments, physical function, and disability in older adults. The FAC will also support innovative developmental projects that seek to develop or further validate innovative approaches to assess musculoskeletal impairments, physical function, and disability in older adults.