The easiest way to analyze muscle activity is to use the EMG channel and the EMG rectified channel on the Go Direct® EKG Sensor (GDX-EKG). You can look at the difference between the maximum and minimum voltage over time to measure EMGs. This is the method in Human Physiology Experiments:
Volume 1 (HSB-HP). Or you can take the integral of the muscle activity. This is an advanced method used in Human Physiology Experiments: Volume 2 (ALB-HP2).

Using a Go Direct® EKG Sensor (GDX-EKG) is the best way to study muscle activity.

You can also 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), but you will get much better results using the Go Direct® EKG Sensor (GDX-EKG).

Always make sure your interface and / or computer or Chromebook you are using is on battery power and are not plugged into a wall socket. You can also use the Potential column for the EKG sensor to look at EMGs. This will give you better signal quality in most cases. Just tap on the Y-Axis and choose Potential. Then deselect EKG.

There are ways to get the EKG Sensor (EKG-BTA) to behave more like the EMG and EMG rectified channels of the Go Direct® EKG Sensor (GDX-EKG).  This requires using calculated columns to perform some signal processing. They are simple to perform, and can be done in Graphical Analysis, Logger Pro and LabQuest App. You may need to purchase Graphical Analysis Pro if you are using Graphical Analysis. Please see the general notes below if you need to use theEKG Sensor (EKG-BTA) in this way.

There are several steps that will need to be performed. The EMG is a rapidly oscillating signal. Signal processing 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 optional 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, LabQuest App and Graphical Analysis Pro

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

Use the following steps to record and analyze EMGs using LabQuest App.

  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 a Column Name (Rectified EMG) and give it 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 using the Potential channel.

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.

Using Graphical Analysis 

Use the following steps to record and analyze EMGs using Graphical Analysis.

  1. Change the data-collection rate to 500 samples/s.
  2. Zero the EKG sensor before collecting data.
  3. Tap the Y-Axis and and Deselect (Toggle Off) EKG.
  4. Tap on the three dots next to the Toggle switch for Potential.
  5. Select Add a Calculated Column from the menu.
  6. Enter the Column Name (Rectified EMG) and Units (mV)
  7. Select Insert Expression
  8. Select A abs (X) as the Equation Type
  9. Verify that A is equal to 1.
  10. Verify that Potential is listed for Column X.
  11. Tap on Apply

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.

RELATED TILs:
Do you have a force sensor that can be used with frog leg or heart muscles?

Published: October 25, 2012. Updated: July 26, 2024.