Can the pliance pressure mat accurately locate the COP position in a standing subject?

Why? Measurement of standing posture common in the assessment of: Neurological disorders (eg. Parkinsons) Affect of age Surgical intervention Strength and conditioning Exercise Sports that require stable base eg. Golf putting, shooting, archery, etc Indicator of postural control

Why? Indicates body’s reaction to accelerations of the COM “Ankle technique” to adjust posture COP always within base of support Indicates position of GRFs

How? Typically, research has been conducted by measuring the displacement of the COP using a force platform

What is calculated? Range of COP movement in AP and ML directions Max y co-ord Min y co-ord Max x co-ord Min x co-ord Total displacement Over total time and at discrete points (1sec, 5sec,etc.) Area COP average velocity

Disadvantages of force plates Portability? Access to subjects limited No discrimination of feet COP of whole body only No information on COP location in feet Unknown distance between feet Proportional L/R weighting unknown (AccuSway requires user to locate feet)

COP measurement using pliance All parameters provided by force plate can be calculated post measurement Range data Area Velocity Total displacement

Comparison of pliance to AMTI Method AMTI strain gauge plate, 500Hz, Pliance mat 392 (16x16, 6cm 2 ), 38.5Hz, 8.2 software Data collection synchronised through Amlab software 1 st picture sync pulse from pliance Many trials, different subjects, different tasks Eliminated trials because of edge data and saturation

COPx v COPy scatter plot examples AMTI data Pliance data

COPx v COPy scatter plot examples AMTI data Pliance data

COPx v COPy scatter plot examples AMTI data Pliance data

Accuracy of pliance COP range data (using AMTI as gold standard – error calculated as difference from AMTI output) Combined range data for all trials COPy pliance (mm) COPy AMLAB (mm) COPx pliance (mm) COPx AMLAB (mm) Mean Stdev Combined Error data for all trials COPy abs (mm) COPy rel (% ) COPx abs (mm) COPx rel (%) Mean Stdev

Accuracy of pliance COP range data Non-central F distribution to assess “equality” Where d is effect size,  is the non-centrality parameter, PD is practical difference Statistical parameters  (mm)  (mm) PD (mm) d  F calcp COPy COPx This indicates that the COP range data from the pliance pressure system is of equal accuracy to the COP output of the AMTI force plate.

Implications for novel Ability of flexible mat to provide accurate COP information in standing subjects Note also that resolution of system was not highest available Many advantages of pliance “posturography” system over force plate systems

Advantages of pliance over force plate Highly portable Go to subjects rather than subjects come to researcher eg. Could measure next to bed in hospital Simple set up (flat surface) Combination with recorder or player

Advantages of pliance over force plate Most importantly analysis can easily provide information on each foot (if double support) COP total range x,y, COP left/right, within foot COP location as % of distance between feet Individual feet loading information (force) Interactions between feet

Future applications/modifications Biofeedback By increasing the size of the display in online mode and centreing display OR bars to indicate left/right loading AND bars to indicate back forward loading OR numerical display to indicate position of COP left/right Collect data with masks Report protocol