Recurrence quantitative analysis of postural sway using force plate and smartphone

Although modern medicine and new medical technologies offer enormous potential to improve diagnosis and treatment of many diseases, mortalities from fall accidents are steadily on the rise for the elderly. Since postural stability characteristics are considered to be important in maintaining functional independence free of falls and healthy life style especially for the growing elderly population, there is an imminent need in inexpensive and portable device that can assess balance. While inertial sensors embedded in smartphone are seen as an alternative to force plate (ground truth) to unobtrusively assess postural stability in home environments, no study has yet reported the non-linear physiological information captured by smartphone affixed at pelvic region. By using recurrence quantitative analysis (RQA), this study investigates non-linear dynamical features of postural sway measured from force plate and smartphone. The resultant position vector of postural sway from the two systems was highly coherent and was used for non-linear analysis. Even though most of RQA measures collected from the projected postural sway using the smartphone were significantly different than measures collected using the force plate, deterministic characteristics of postural sway were not found significantly different. This study opens new prospects of easy clinical testing using postural variables that may be relevant for assessing fall risks at home and patient environment in future.