Winter 2014

1

HPHY 333 - Motor Control

Lab 5 - Balance Control

Lab 5 focuses on the evaluation of postural control under relatively static conditions. The response of the Central Nervous System (CNS) will be examined secondary to a number of different manipulations of sensory input during quiet stance. Essentially, weighting of incoming sensory information will be switched from one system to another and we will observe how the CNS responds. The measure we will use to characterize the CNS’s response to changes in sensory information will be changes in the displacement of the center of pressure (COP). COP indicates the location of a point where the resultant of all vertical ground reaction forces act on the body, representing a weighted average of all the pressures over the surface of the area in contact with the ground (Winter, 1990). For example, during quiet stance, there is a separate COP point under each limb but the overall COP lies between two feet and its location varies depending on the weight that each limb supports. If you lift up your right leg, the COP will shift toward to your left side. Changes in the displacement of the COP reflect the neuromuscular response to imbalances of the body’s center of mass (COM). In the current lab, we will evaluate how the overall displacement of the COP across various conditions. This will provide you with an idea of how manipulation of sensory input impacts CNS responses. The main measures you will examine are the range of motion of the COP in the anterior-posterior direction as well as the total path of the COP. We will manipulate vision and somatosensation at the feet in isolation and in combination to see how each affects the balance response of the CNS. In addition, we will examine COP displacement measures with respect to anticipatory postural adjustments. Step1: Force Plate System Set-up During this lab, you will be asked to familiarize yourself with the force-plate system. This laboratory experience will allow you to become proficient at collecting data during quiet stance. Please refer to the step-by-step guidelines on how to use the system.

1) Turn on the control boxes for the Motion Analysis and AMTI Force Plate systems. 2) Hit “Zero” button at the control box of the AMTI Force Plate to make sure the platform

offset is zero. 3) Turn on the computer and launch Cortex software icon on the Desktop.

Remember to turn on the control boxes BEFORE launching Cortex software. 4) Load Setup file from your working folder

- From the Menu Bar, select File > Load Setup… - Load “HPHY333.cal”

Step2: Data Collection Preparation

1) Select two panes: the top pane for a 3D view and the bottom pane for an Analog Graph view. - From the Menu Bar, select Layouts > 2 Panes: Top/Bottom

Winter 2014

2

- Click the Top Pane (you will see an orange square around the pane): From the Menu Bar, select Data Views > 3-D View

- Click the Bottom Pane (you will see an orange square around the pane): From the Menu Bar, select Data Views > Analog Graphs

2) Select F1Z as the visible channel on the Analog Graphs pane. - Right click on the Analog Graphs and select F1Z (unclick others).

3) Open the Force Plate Window - From the Menu Bar, select Tools > Force Plate Data…

4) Connect to Cameras and Click Play button 5) Have the subject stand on the Force Plate and make sure the data makes sense

- View the Analog Graph and see if F1Z data starts from Zero (If not, hit “Zero” button at the control box of the AMTI Force Plate).

- Read the FZ value in the Force Plate Data window (Force Units: Newtons) and see if the value matches the subject’s body weight.

Start Data Collection 6) Select required raw data and capture duration.

- From the Record Bar, select Recording Settings… - Select Raw Camera Data (VC*), Analog (ANB), Tracked Binary(TRB) - Set the capture duration to 5 seconds

7) Name your file. 8) When the subject is ready, the experimenter clicks the Record button. The computer

will collect data for 5 seconds. Be sure the postural event related to the experimental condition is met within the 5 seconds of your recording.

Experimental Procedure The subject will perform three tasks and each task will be performed with eyes-open and eyes-closed conditions: 1. Quiet stance with eyes open & Quiet stance with eyes closed 2. Stance on a foam pad with eyes open & Stance on a foam pad with eyes closed 3. Catching an object with eyes open & Catching an object with eyes closed

1) During the first task, one group member will remove his/her shoes, and stand on the center of the force platform with feet approximately shoulder-width apart and with his/her frontal plane lined up with the x coordinate of the platform (labeled on the side of the platform). The subject will be instructed to stand still for four seconds with eyes open. We will record the motion of the subject’s COP movement in both the x and y directions.

2) After collecting and saving the last four seconds of data for quiet stance with eyes open, the subject will be asked to perform the same quiet stance task but with eyes closed. It is imperative that the subject places his/her feet at the same location when he/she closes the eyes.

3) Place a piece of foam on top of the force plate and repeat the first task. Both eyes-open and eyes-closed conditions will be performed.

Winter 2014

3

4) Remove the piece of foam from the force plate and repeat the first task. While the subject is standing quietly, s/he will be asked to catch a weight dropped nicely into his/her hands. The first catch will be with eyes open and the second will be with eyes closed.

Step3: Data Process 1) Once you finish data collection, disconnect the camera and change it to Post Process

mode. 2) Select two panes under the Post Process mode: the top pane for a 3D view and the

bottom pane for analog data. - From the Menu Bar, select Layouts > 2 Panes: Top/Bottom - Click the Top Pane (you will see an orange square around the pane): From the Menu

Bar, select Data Views > 3-D View - Click the Bottom Pane (you will see an orange square around the pane): From the

Menu Bar, select Data Views > Analog Graphs 3) Load Setup file and Capture files

- From the Menu Bar, select File > Load Setup… - Select the Setup file (HPHY333.cal) under your working folder - From the Menu Bar, select File > Load Capture… - Select the Capture file under your working folder that you want to process.

4) Read the Force Plate data - From the Menu Bar, select Tools > Force Plate Data…

5) There are FX, FY, FZ, X, Y, Z, MZ information representing force values in X, Y, Z axes (FX, FY, FZ; unit: Newtons), COP position in X, Y, Z axes (X, Y, Z; unit: mm) and moment in Z axis (MZ; unit: Newtons-mm). When you are facing the computer, X is the anterior-posterior direction, Y is the medial-lateral direction, and Z is the superior-inferior direction toward the ceiling.

6) Export Data - From the Menu Bar, select File > Export > Export Forces File… - Name your file and save it to your working folder

7) Read Data - You can open the *Forces file via Excel - We need #Sample, X1, and Y1 for data analysis

Sample Rate of this experiment is set at 60.00 Hz. Step 4: Data Analysis You will be asked to graph the COP deviation in the anterior-posterior (in X axis) plane as a function of time for each condition (plot Time v.s. COPx deviation). You will, therefore, have three graphs: one for each task. On each graph, you will be required to plot two lines, one representing the eyes-open condition and the other representing the eyes-closed condition. Use these graphs to answer the questions in the discussion section. You will first insert a Time Column. Since the sample rate is 60.00Hz, you will transfer the #Sample to Time by dividing #Sample by 60. For the COPx deviation, use the X1 column.

Winter 2014

4

You will also be required to calculate and graph the total travel path of the COP. The total path of the COP is defined as the total distance traveled by one’s COP during each trial. Use Excel and the equation” = ABS(cell 2 – cell 1)” to calculate the absolute value difference between consecutive data points within a column of data for both x and y directions. Provide a table (Table 1) for the 6 combinations of conditions. In addition, provide six graphs of the COP trajectory (plot COPx v.s. COPy) for each condition. Table 1: Total travel path of the COP in six conditions.

Conditions Quiet stance with eyes open

Quiet stance with eyes closed

Stance on a foam pad with eyes open

Stance on a foam pad with eyes closed

Catching an object with eyes open

Catching an object with eyes closed

Total COPx

Total COPy

Total COPx +Total COPy

When answering the questions, please use your graphs for a qualitative analysis of your data, and the total path of COP for the quantitative perspective. Identify pertinent sources for error in the lab in the event of imperfections in the data. Lab Report (50 points) Write a two-page single-spaced lab report including introduction, methods, results, and discussion. Tables and Figures do not count toward the two-page requirement. In the results section, provide (A) three graphs for the COP deviation in the sagittal plane (Time v.s. COPx deviation) for each task. Each graph should have two lines on it representing eyes open and eyes closed respectively. In addition, you should provide (B) a table summarizing the total paths of the COP (Total COPx +Total COPy) for each condition (Table 1) and (C) six graphs for the COP trajectory (COPx v.s. COPy) for each condition. DO NOT turn in your raw data sets. Include a short description of the results in a caption below each figure and table. In the discussion section, include answers to the following questions: 1. Which direction did the COP move when the subject swayed forward? What sensory information would the subject use to sense this forward sway? 2. Using the total path of the COP data, what happened to the ability to control balance with the eyes closed? What about standing on foam? Which manipulation led to the biggest change in balance control? What does this tell you about the contribution to balance control of each system that we manipulated?

Winter 2014

5

3. For the condition in which the mass was dropped into the hands, what effect did closing the eyes have on the response? Why do you think this occurred? Refer to the lab report guidelines and grading rubric (provided on Blackboard) for details on preparing the lab report.