Freezing of gait shapes the postural control of individuals with Parkinson's disease: Effect of visual information and medication states.

Background: Several measures of the center of pressure have been used to describe magnitude and structure of the postural sway in individuals with Parkinson's disease (PD). This study aimed to examine whether both the magnitude and structure of the center of pressure trajectory can differentiate PD individuals with and without freezing of gait in both On- and Off-medication states and with eyes open and closed.

Methods: Twenty-four individuals with PD (14 without and 10 with freezing of gait) were tested. Participants stood as still as possible on a force plate for 30 s with eyes open and closed and On- and Off-medication. Analyses of variance were used to test the effect of group, medication state, and visual information on the magnitude (area) and structure (shape measured by the ratio between axes length and orientation) of the center of pressure ellipses.

Findings: The center of pressure ellipses were less elongated in On-medication state and for PD with freezing of gait than without freezing of gait. Moreover, the magnitude of the ellipses was larger for PD with freezing than without freezing of gait only in the On-medication state. The orientation of the ellipses was more diagonal for individuals with freezing, in the On-medication state, and with the eyes closed when compared to individuals with PD without freezing under the same conditions.

Interpretation: Magnitude and structure of the postural sway differed between PD individuals with and without freezing of gait, depending on the medication state and the availability of the visual information.