Objective measurement of dynamic balance function by the simultaneous measurement of the center of gravity (COG) and center of pressure (COP)

Although a posturography is commonly used for objective evaluation of static balance function, dynamic balance function is usually evaluated only with clinical scales. Simplified objective measurement systems for the evaluation of dynamic balance function need to be developed. In this preliminary study, we attempted to develop an index for the objective measurement of dynamic balance function from COP-COG data. The subjects comprised nine hemiparetic post-stroke patients and five healthy subjects. The simultaneous measurements of COG and COP were performed using a three-dimensional motion analysis system (Kinema-tracer, KisseiComtec, Japan) combined with force plate analysis. As indices for evaluating dynamic balance function, the latency of COP passing COG after heel contact (LCP) and the averaged |COP| − |COG| subtraction value during stance phase (ASV) were calculated. For evaluating validity of the measurement, the Berg Balance Scale, a frequently used clinical balance scale, was used. The results showed significant differences (0.13 ± 0.02 vs. 0.29 ± 0.23 s) between the healthy subjects and patients in LCP, and large, yet insignificant, differences (4.3 ± 0.5 vs. 2.7 ± 2.0 cm) in ASV. The ASV was strongly correlated with BBS. A strong correlation was observed between COG acceleration and ASV, except in one patient, who had a severe balance disorder. These results may encourage further investigation into the feasibility of COP-COG measurements for balance measurement.