Can the pliance pressure mat accurately locate the COP position in a standing subject?
Jan 24, 2016
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