The easiest way to analyze muscle activity is to use the EKG Sensor (EKG-BTA) as an EMG sensor and look at the difference between the maximum and minimum voltage over a given time period. This method is used in Human Physiology with Vernier (HP-A).
There are more accurate ways to compare EMG activity (the electrical activity from a muscle), but they require filtering and signal processing. They are not as simple to perform but can be done in Logger Pro or LabQuest App.
The standard way of analyzing an EMG involves a series of steps. The EMG is a rapidly oscillating signal. Filtering is used to create an envelope around the electrical activity so it can be quantified.
First, any offset before activity needs to be reduced to 0 mV. Then the data are filtered to get rid of low frequency noise artifacts. The signal is then rectified so that all the negative peaks from the EMG trace are positive. An integral decay function is then applied to the EMG signal. Last, a standard integral is performed over the area of the filtered and processed data that corresponds to the EMG activity. The area under the curve that corresponds to EMG activity is what is typically measured.
You can follow the steps below to analyze EMG activity using Logger Pro or LabQuest App.
Using Logger Pro
1. Choose Open from the File menu. Open the EMGwDecayParameter file found in the EKG Probes and Sensors folder. This file automatically performs all of the functions that you need to do to analyze an EMG.
2. Zero the EKG sensor before you begin data collection.
3. Begin Data Collection. Please note that this file uses a data-collection rate of 500 samples/s.
Data Analysis
This file consists of two pages. The first page has two graphs. The first graph shows the raw EMG signal. The graph below shows the filtered EMG signal. There is a parameter control in the bottom left hand corner that you can use to adjust the filtered data. The default setting is 3 Hz.
Page 2 also has two graphs. The first graph is the rectified EMG data. The graph below it is the EMG data with a Decay Filter applied. The default setting for this parameter is 0.1 seconds.
To analyze EMG activity, select the region in the second graph on Page 2 that corresponds with EMG activity. Choose Integral from the Analyze menu. Write down the value of the integral.
Using LabQuestApp
Filtering is not available in LabQuest App at this time, but you can use the following steps to analyze EMGs.
1. Change the data-collection rate to 500 samples/s.
2. Zero the EKG sensor before collecting data.
3. Tap Table and choose New Calculated Column from the Table menu.
4. Enter the Name (Column Rectified EMG) and Units (mV).
5. Select Abs(X)as the Equation Type.
6. Select Potential for the Column for X.
This calculated column will now display the rectified EMG data for your run.
Begin Data Collection.
To analyze the EMG, select the region of the rectified EMG that corresponds with muscle activity. Then Analyze the region selected by using the Integral function.
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