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, 6cm2), 38.5Hz, 8.2 software

Data collection synchronised through Amlab software 1st 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

KM stand right 1 COP amlab

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

-0.08 -0.06 -0.04 -0.02 0 0.02 0.04

COPy range 9.96cm

CO

Px

rang

e 5.

83cm

KM stand right 1 COP pliance

18

19

20

21

22

23

24

25

10 12 14 16 18 20 22

COPx range 9.79cm

CO

Py

ran

ge

5.69

cm

AMTI data Pliance data

COPx v COPy scatter plot examples

COP putt 4_2 amlab

0.02

0.022

0.024

0.026

0.028

0.03

0.032

0.034

0.036

0.02 0.025 0.03 0.035 0.04

COP Y range 1.479cm

CO

P X

ra

ng

e 1

.12

2c

m

COP putt 4_2 mat

19.8

20

20.2

20.4

20.6

20.8

21

21.2

19.5 20 20.5 21 21.5

COP X range 1.47cmC

OP

Y r

ange

1.1

2cm

AMTI data Pliance data

COPx v COPy scatter plot examples

COP putt 4_1 mat

2121.221.421.621.8

2222.222.422.622.8

20.2 20.4 20.6 20.8 21 21.2 21.4

COP X range 0.99cm

CO

P Y

ra

ng

e 1

.37

cm

COP putt 4_1 amlab

0.03

0.035

0.04

0.045

0.05

0.027 0.029 0.031 0.033 0.035 0.037 0.039

COP Y range 0.978cm

CO

P X

ra

ng

e 1

.37

3c

m

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 19.71 19.44 11.88 11.78

Stdev 21.68 21.28 5.35 5.2

Combined Error data for all trials

COPy abs (mm)

COPy rel(% )

COPx abs (mm)

COPx rel(%)

Mean 0.27 1.67 0.11 0.37

Stdev 0.75 4.07 0.44 4.62

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 calc p

COPy 19.57 21.29 0.979 0.172 0.122 0.002 0.033

COPx 11.83 5.23 0.59 0.423 0.297 0.006 0.053

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