The Vernier System

THE VERNIER SYSTEM

ELECTROMYOGRAM (EMG)

RELATIONSHIP BETWEEN MUSCLE ELECTRICAL ACTIVITY AND FORCE

PROCEDURE

I.Laptop Computer and LabQuest Unit Setup

A.LabQuest Unit

1.Plug in charger/transformer into a 110V AC outlet, and connect the power line to the LabQuest Unit (left side).

2.Attach USB cable (small end) to LabQuest Unit (upper end).

3.Attach USB cable (large end) to laptop computer (left side).

4.Plug in the Voltage (EKG) transducer into connector #1 of the LabQuest Unit (upper end).

5.Plug in the Force transducer (Hand Dynomometer) into connector #2 of the LabQuest Unit (upper end).

6.Turn the power on to the LabQuest Unit (button on upper left corner of unit).

B.Laptop Computer

1.Plug in charger/transformer into a 110V AC outlet, and connect the power line to the laptop computer (left side, back).

2.Turn on the laptop computer

3.Double click on the Macintosh HD icon to open the Macintosh HD menu.

4.Double click on the Applications folder.

5.Double click on the Logger Pro 3 folder.

6.Double click on the Experiments folder.

7.Double click on the file:18 EMG and Muscle Fatigue

a.Two graphs and a table should appear on the screen.

1)Force (N=neutons) vs. Time (s)

2)Potential (mV=millivolts) vs. Time (s)

C.Set Up Force and Voltage (potential) transducers

1.Zero the readings for the Hand Dynamometer.

a.Click the Zero button, .

b.Hold the Hand Dynamometer along the sides, in an upright position (see Figure 2). Do not put any force on the pads of the Hand Dynamometer.

c.Click the box in front of Hand Dynamometer to select it and click .

2.Attach three electrode tabs to on of your arms, as shown in Figure 3. Two tabs should be placed on the ventral forearm, 5 cm and 10 cm from the medial epicondyle along an imaginary line connecting the epicondyle and the middle finger.

3.Attach the green and red leads to the tabs on ventral forearm. For this activity, the green and red leads are interchangeable. Attach the black lead to the upper arm.

4.Have the subject sit with his/her back straight and feet flat on the floor. The elbow should be at a 90° angle, with the arm unsupported.

5.Adjust Graph settings

a.Click on the Force graph.

1)Go to the Options menu (top of screen)

a)Click on Graph Options

1]Click on Axes Options

a]Go to the Y-axis section

1}set the top value to 100 N

2}set the bottom value to 0 N

b]OK

a.Click on the Voltage (Potential) graph.

1)Go to the Options menu (top of screen)

a)Click on Graph Options

1]Click on Axes Options

a]Go to the Y-axis section

1}set the top value to +0.5 mV

2}set the bottom value to -0.5 mV

b]OK

II.Experiment

A.Procedure

1.Go to the Experiment menu (top of screen).

a.Click on the Zero selection.

1)This will set the starting values for both the Force (Hand Dynomometer transducer), and Voltage (EKG transducer) to zero (again).

b.Click on the Start Collection selection.

1)Hold the Force on the Hand Dynomometer as consistently as possible for 10 seconds at each of the forces; 20, 40, 60, 80 N.

III.Data Analysis

A.Procedure

1.Force Analysis

a.On the Force graph highlight the most consistent range of Force data associated with each of the different Force levels.

1)This is usually toward the end of the ten-second period when the subject has learned to keep the Force steady.

a)Try to highlight at least a five second segment of Force values.

2)Place the cursor on the graph where the most consistent Force recording starts, then click and drag the cursor to the end of the consistent Force segment.

a)Brackets will appear at the start and end points of the highlighted range of recorded values.

b.Go to the Analyze menu (top of screen)

1)Click on Statistics

a)Move (click and drag) the statistics box off of the Force graph.

b)Record the mean (average) Force values (N) in a table, associated with each of the ten-second periods (0-10,10-20,20-30,30-40).

c.The easy way to obtain the statistics for the next voltage/force (V/F) section is to move the end and start brackets to the range of consistent data for the next section.

1)Click and drag the end-value bracket to the end of the consistent data segment for the next V/F section.

2)Click and drag the start-value bracket to the beginning of the consistent data segment for the next V/F section.

3)The data in the Statistics box will change to the correct values for the newly bracketed section.

4)Record the mean (average) Force values (N) in a table.

2.Voltage Analysis

a.On the Voltage graph highlight the most consistent range of voltage data associated with each of the different Force levels.

1)This is usually toward the end of the ten-second period when the subject has learned to keep the Force steady.

a)Try to highlight at least a five second segment of voltage values.

2)Place the cursor on the graph where the most consistent voltage recording starts, then click and drag the cursor to the end of the consistent voltage segment.

a)Brackets will appear at the start and end points of the highlighted range of recorded values.

b.Go to the Analyze menu (top of screen)

1)Click on Statistics

a)Move (click and drag) the statistics box off of the Voltage (Potential) graph.

b)Record the Voltage values (mV) for the maximum, minimum, and Standard Deviation (SD) in a table, next to the associated Force.

c.The easy way to obtain the statistics for the next voltage/force (V/F) section is to move the end and start brackets to the range of consistent data for the next section.

1)Click and drag the end-value bracket to the end of the consistent data segment for the next V/F section.

2)Click and drag the start-value bracket to the beginning of the consistent data segment for the next V/F section.

3)The data in the Statistics box will change to the correct values for the newly bracketed section.

4)Record the Voltage values (mV) for the maximum, minimum, and Standard Deviation (SD) in a table, next to the associated Force.

d.The electrical activity of the muscle is shown by the magnitude of the voltage change (the average extent of the vertical range of the voltage values over the selected segment).

1)The overall extent of the vertical range of the voltage values is calculated by the difference between the maximum and minimum values.

a)However, since the force is hard to hold consistent the voltage will also be inconsistent, with unrepresentative high and low values.

b)So, the overall extent of the voltage change does not necessarily shown the average change in the voltage.

2)The average extent of the vertical range of the voltage values can be estimated by using two times the Standard Deviation (SD) value.

a)The SD is a way of stating, in a standard way, how far the measured values deviate (are different from) the average.

b)The SD number gives the range to both sides of the average value that would contain 67% of all the measured values.

1]So, if there were 100 measured values the 2xSD would give the range around the average that would contain 67 of the measured values.

c)So, if the muscle force and electrical activity are greater, then the average voltage change will be greater, and thus the SD will be larger.

e.Plot the Voltage on the y-axis and the Force on the x-axis of the graph.