[Measurement of the center of gravity using the link model for controlling functional electrical stimulation]

The purpose of this study is to better understand the reliability of using the link model when determining the center of gravity. We measured the centers of gravity using both the link model and the floor reaction force in 11 healthy subjects. Dempster's and Clauser's anthropometric data were used in measuring the center of gravity by the link model, and these results were compared with those measured by the floor reaction force. The motion area of the center of gravity during quiet standing was determined by experimental data, using the link model calculation. Joint torque was measured using Cybex II in one paraplegic patient who was treated by functional electrical stimulation (FES). We discuss whether the paraplegic patient can stand safely in a determined center of gravity motion area. Displacements of the center of gravity measured by the link model were very close to those obtained by the floor reaction force. The parameters of body segments proposed by Dempster were more reasonable than those of Clauser. The maximum differences of the center of gravity between those measured by the link model using Dempster's data and those measured by the floor reaction force, were 1.47 cm for the fore-aft direction, 1.85 cm for the lateral direction, and 2.34 cm for the vertical direction. The torque caused by electrical stimulation was stronger than that calculated by the link model during quiet standing. Our results suggest that the link model system that measures displacement of the center of gravity using Dempster's data, is clinically applicable for the closed-loop control system of FES.