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

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

2. 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

3. 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

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

5. 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

6. 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)

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

8. 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

9. COPx v COPy scatter plot examples AMTI data Pliance data

10. COPx v COPy scatter plot examples AMTI data Pliance data

11. COPx v COPy scatter plot examples AMTI data Pliance data

12. Combined range data for all trials Combined Error data for all trials COPy pliance (mm) COPy abs (mm) COPy AMLAB (mm) COPy rel (% ) COPx abs (mm) COPx pliance (mm) COPx AMLAB (mm) COPx rel (%) Mean 0.27 1.67 0.11 0.37 Mean 19.71 19.44 11.88 11.78 Stdev 0.75 4.07 0.44 4.62 Stdev 21.68 21.28 5.35 5.2 Accuracy of pliance COP range data (using AMTI as gold standard – error calculated as difference from AMTI output)

13. 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 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 • 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.

14. 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

15. 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

16. 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

17. 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