Walking speed is "almost the perfect measure." A reliable, valid, sensitive and specific measure, self-selected walking speed (WS), also termed gait velocity, correlates with functional ability, and balance confidence. It has the potential to predict future health status and functional decline including hospitalization,11 discharge location and mortality. Walking speed reflects both functional and physiological changes, is a discriminating factor in determining potential for rehabilitation and aids in prediction of falls and fear of falling. Furthermore, progression of WS has been linked to clinical meaningful changes in quality of life and in home and community walking behavior. Due to its ease of use and psychometric properties, WS has been used as a predictor and outcome measure across multiple diagnoses. In addition, WS was chosen by a panel of experts as the standardized assessment to measure locomotion for the Motor Function Domain of the NIH Toolbox.