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.