A markerless system based on smartphones and webcam for the measure of step length, width and duration on treadmill

Background and objective: A markerless low cost prototype has been developed for the deter-mination of some spatio-temporal parameters of human gait: step-length, step-width andcadence have been considered. Only a smartphone and a high-definition webcam have beenused.Methods: The signals obtained by the accelerometer embedded in the smartphone are usedto recognize the heel strike events, while the feet positions are calculated through imageprocessing of the webcam stream. Step length and width are computed during gait trials ona treadmill at various speeds (3, 4 and 5 km/h).Results: Six subjects have been tested for a total of 504 steps. Results were compared withthose obtained by a stereo-photogrammetric system (Elite, BTS Engineering). The maximumaverage errors were 3.7 cm (5.36%) for the right step length and 1.63 cm (15.16%) for the rightstep width at 5 km/h. The maximum average error for step duration was 0.02 s (1.69%) at5 km/h for the right steps.Conclusion: The system is characterized by a very high level of automation that allows itsuse by non-expert users in non-structured environments. A low cost system able to auto-matically provide a reliable and repeatable evaluation of some gait events and parametersduring treadmill walking, is relevant also from a clinical point of view because it allows theanalysis of hundreds of steps and consequently an analysis of their variability.