I. Introduction
Walking speed is a valid predictor of health status in a wide range of clinical populations [1]. Low walking speed is associated with increased risk of falls, cognitive impairment, and institutionalization in older adults [2], [3]. Conversely, improvements in walking speed have been correlated with better quality of life in patients with Parkinson's disease [4], multiple sclerosis [5], stroke [6] and cerebral palsy [7]. Moreover, self-selected gait speed represents a major outcome in many exercise-based rehabilitation programs [8].