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.