PHASE PLANE ANALYSIS OF STABILITY IN QUIET STANDING

We analyzed the standing balance control of 11 healthy subjects and 15 subjects with bilateral vestibular hypofunction (BVH) using phase pla ne (velocity versus displacement) plots. We hypothesized that maintain ing postural stability requires control of both the position and momen tum of the center of gravity (CG) and infer that it is advantageous to use both velocity and displacement data to characterize balance contr ol. Phase balance control We evaluated phase plane plots based on whol e body CG and center of pressure (CoP). We varied stability by alterin g the base of support and visual information. Three different foot pla cements were used: feet wide apart, feet together, and semitandem stan ce. Feet together standing was performed with eyes open and with eyes closed. The phase plane plots show changes in stability as base of sup port is altered or visual input is removed and reveal stability differ ences between the control and BVH groups. The root mean square varianc e of velocity and displacement was used to quantity the phase plane in formation. This parameter showed significant differences between activ ities and between groups. We conclude that phase plane plots that comb ine displacement and velocity information are more useful in character izing balance control than displacement or velocity alone.