Reliability and Validity of the Index of Postural Stability Using Forceplates

Abstract

The aim of this study was to assess reliability and validity of Index of Postural Stability (IPS); a new index for assessing postural stability using forceplates. Nineteen healty subjects and 21 patients with balance disorder mainly due to neurological diseases were participated in this study. IPS was defined following equation; IPS=log [(area of stability limit + area of postural sway)/area of postural sway]. Each subject stood still with medial border of his/her feet 10 cm apart on the forceplates. Postural away was measured during 10 seconds in the central position and anterior, posterior, right and left weight shifting position on a base of support, respectively. The area of postural sway was calculated as the mean of sway area of five positions. The area of stability limit was defined as the length between the center of sway in right weight shifting position and left weight shifting position multiplied by the length between anterior position and posterior position. Reliability of IPS was assesssd by intra-class correlation between two measurements on different day. Validity of IPS was assessed by its relation to Berg Balance Scale (BBS). Intra-class correlation between-days measurement of IPS was high (ICC=0.999). And the correlation of IPS with BBS was also high (rs=0.855). In this study, reliability and validity of IPS were both high, we therefore conclude IPS is a good index for assessing the ability of postural stability.