Early Postural Instability in Parkinson’s Disease: A Biomechanical Analysis of the Pull Test

Table 1

Posturographic variables.

Posturographic variables	Definition
General statistics (cm):
X avg	Average displacement of the CoP in the lateral (X) axis of the platform
X right	Maximum displacement of the CoP in the right direction
X left	Maximum displacement of the CoP in the left direction
X SD	Standard deviation of the mean displacement of the CoP in the lateral (X) axis
Y avg	Average displacement of the CoP in the anterior-posterior (Y) axis of the platform
Y ant	Maximum displacement of the CoP in the anterior direction
Y post	Maximum displacement of the CoP in the posterior direction
Y SD	Standard deviation of the mean displacement of the CoP in the anterior-posterior (Y) axis
Velocity measures (cm/s)
Vx right	Maximum velocity of the CoP in the right direction
Vx left	Maximum velocity of the CoP in the left direction
Vy ant	Maximum velocity of the CoP in the anterior direction
Vy post	Maximum velocity of the CoP in the posterior direction
V avg	Average velocity of the CoP
Sway areas (cm^2)
Rectangular area	Rectangular area that encompasses 100% of the data
Circular area	Circular area that encompasses 100% of the data
Area95	95^th percentile of an ellipse fitted to the overall CoP trace
Major95 (cm)	Length of the major axis of the 95^th percentile ellipse
Minor95 (cm)	Length of the minor axis of the 95^th percentile ellipse
Path length (cm)	Total distance covered by the CoP

CoP: center of pressure; cm: centimeters; s: seconds.