Linking digital assessment of mobility to clinical endpoints to support regulatory acceptance and clinical practice The purpose of the action is to measure in three chronically ill or frail populations (e.g. heart failure, multiple sclerosis, Parkinson’s disease, COPD, frailty/sarcopenia, post-hip fracture):as a primary outcome, real world walking speed (RWS);as secondary outcomes, additional digital mobility assessment (step counts, time walking, gait characteristics, time sitting/standing/walking, cadence, estimated energy expenditure of physical activity, etc.) to be collected and compared (or combined) with RWS to identify outcomes of maximum predictive power. The action will demonstrate that RWS or one of the other gait parameters predicts relevant medical outcomes (falls, injurious falls, hospitalisations, loss of activities of daily living [ADLs], death), and achieve regulatory recognition of RWS as a surrogate endpoint independently of underlying disease diagnosis. To do this, regulatory submission for qualification opinion is anticipated. Loss of mobility is a growing unmet medical need, driven by chronic illness and frailty in the elderly and by injury in the young. Loss of mobility is a key morbid effect of diseases of various organ systems, including chronic obstructive pulmonary disease (COPD), heart failure, multiple sclerosis, neurodegenerative diseases, etc. New therapeutic approaches target restoration of function and mobility in patients with degenerative diseases, acute injuries, and age-related disabilities, such as muscle anabolic drugs, cartilage regeneration approaches, and other therapies targeting the musculoskeletal system.However, current primary endpoints that measure mobility are either based on patient reported outcome or performance testing, both of which have significant shortcomings.To ensure full acceptance and integration of digital mobility assessment into clinical trials and utilisation as primary or secondary endpoint, there is a need for rigorous validation and linkage to clinically relevant ‘hard’ endpoints, such as death, disability, falls, or other complications. By making mobility assessment feasible, and indeed an integral part of medical care, this could enable development of novel solutions (pharmacological, digital, nutritional, exercise-based) to a major public health problem – the increasing prevalence of mobility disability due to the aging of the population and chronic diseases. The digital assessment of mobility is such a method, and has the potential to revolutionise the care of frail populations and of the development of drugs to treat them.Successful demonstration that digitally-detected low mobility predicts relevant clinical outcomes will have major impact on drug development and clinical care of the target population.