A unified framework for the measurement of mobility in older persons

Mobility is often referred to as a 'sixth vital sign' because of its ability to predict critical health outcomes in later adulthood. In the World Health Organization (WHO) World Report on Aging and Health, mobility is described as movement in all its forms whether powered by the body or a vehicle. As such, mobility encompasses basic physical actions such as getting up from a chair and walking, as well as activities such as exercising, driving and using public transportation. A plethora of measurement tools have been developed to assess various aspects of mobility; however, there is wide variability in the mobility constructs being measured which limits standardisation and meaningful comparison across studies. In this paper, we propose a comprehensive framework for measuring mobility that considers three distinct facets of mobility: perceived mobility ability ('what can you do'), actual mobility ability ('what you actually do') and locomotor capacity for mobility ('what could you do'). These three facets of mobility are rooted in the three components of healthy aging endorsed by the WHO: functional ability, intrinsic capacity and environments. By proposing a unified framework for measuring mobility based on theory and empirical evidence, we can advance the science of monitoring and managing mobility to ensure functional ability in older age.