Download CofP analysis project - Illinois State University

Illinois State University
School of Kinesiology and Recreation
KNR 352, Quantitative Analysis in Biomechanics
Center of Pressure Project
Data Collection Descriptors
One leg stance, 2 conditions: Eyes Open, Eyes Closed
Sample Rate: 100 Hz, 16 second duration
Subject Mass: 80 kg
CPx: in the anteroposterior direction
CPy: in the mediolateral direction
Two spreadsheets are provided: Eyes Open, Eyes Closed
Reference: Hasan et al, Journal of Biomechanics, 1990 (available on web)
The AMTI force platform output 3 orthogonal forces and three moments around the axes of the
forceplatform. After processing, output from the ground reaction analysis module of our Vicon-Peak
Motus software consists of 10 columns of data: 3 forces (FAP, FML, FV), 3 moments (MML, MAP, MV), 2
center of pressure measures (CofPAP, CofPML), a free vertical moment around the CofP, and the
GRFRESULTANT.
The CofP is the point of application of the resultant GRF on the top surface of the forceplatform. It is
critical when calculating joint torques. It has recently become an important measure clinically to
quantify sway/balance.
In this project, you will use Excel to create stabilograms (scatter plots of the AP and ML CofPs), and
calculate some of the basic measures used to quantify sway (ML and AP ranges, ML-AP area, and CofP
velocities).
1) When we collect sway measures, our procedure is as follows:
a. Set a trigger value on the AD data logger
b. Set data collection for 1 second pre-trigger, and 15 seconds post-trigger
c. Have subject stand comfortably beside the FP
d. Subject steps laterally onto force platform (this will trigger data collection)
e. Monitor subject to ensure they are balanced
f. Have subject step off force platform
2) The raw signals from the force platform are converted to GRF and moments, and the other
measures are calculated.
3) Data are exported to an ASCII file for later processing
4) The last 10 seconds of the collected data are used in the analysis. This provides the subject with
several seconds to become stationary on the force platform.
Procedures for each condition
1) Open the Excel file
2) Remove the first six seconds of the data, leaving only 10 seconds of the trial
3) Create a stabilogram of the CP data. To align with the subject standing on the force platform,
the vertical axis of the stabilogram should be the CPx and the horizontal axis should be CPy.
a. Use the same axis dimensions for both of the stabilograms
4) Perform the following calculations
a. Calculate the average weight of the subject over the trial.
b. Calculate the range of positions in the X and the Y direction
c. Calculate the XY area
d. Using the equations provided for the kinematics assignment, calculate the Xvelocity and
the Yvelocity of the CP.
e. Calculate the resultant velocity of the Center of Pressure.
Your completed work will consist of
1) The two stabilograms
2) A table presenting the values of each of the variables in part 4 from the eyes closed and the eyes
open condition.
3) A description of the similarities/differences in the variables between the two conditions, and an
explanation of your observations.