A technique for quantifying the response of seated individuals to dynamic perturbations

A technique is presented for monitoring the seated postural stability and c ontrol of human subjects. Estimates are made of the locations of the subjec t's center of pressure (CPS) and projection of the center of mass (CMNP) fr om moment balance equations using measured force and acceleration data. The CPS and CMNP indices describe the stability of the subject, independent of the chair, even in the presence of perturbations. The measurement system w as evaluated for both rigid objects and human subjects situated in a wheelc hair undergoing displacement. Estimated CMNP was within +/-5 mm of the actu al value for static loads, For human subjects, the average correlation coef ficient between the estimated CMNP signal and that computed from video data was 0.90; however, transient overestimation of displacement was seen durin g subject acceleration. The technique could help to better assess seated st ability in dynamic environments, such as those experienced by wheelchair us ers in motor vehicles.