Amplitude Analysis: Normalization of EMG to Maximum Voluntary Contraction (MVC)

MVC normalization is a commonly used amplitude analysis technique on EMG signals. This post-processing method utilizes a maximum root mean square (RMS) value from a recording to normalize subsequent EMG data series. The output is displayed as a percentage of the MVC (%MVC) value, which can be used to easily establish a common ground when comparing data between subjects.

EMG signals have a user-dependent nature, causing recordings to differ even when measuring from the same location with the same motion. Therefore, a MVC normalization can be used in order to eliminate this variance and allow for data comparison between subjects to take place.

This step-by-step blog will detail how to perform such a technique using EMGworks Analysis software and its built-in calculation tools, EMGscripts.

MVC Normalization Instructions:

1. Open EMGworks Acquisition and setup your test configuration (sensors, test operator/subject). If you are unsure on how to do so, details can be found here.
2. Within your configuration, there will be a toolbar on the left side of the program window. Select the Experiment Workflow header.
3. In order to perform the normalization you will need at least (2) Plot and Store templates.
   1. MVC trial
   2. Any number of subsequent EMG trials (to be normalized)

Note: as long as you have a MVC trial any other EMG runs can be normalized, not just those recorded alongside the MVC trial.

4. Set the Plot and Store run time and names accordingly. Typically, MVC run times are short as they only require a maximum contractile force to be reached.
5. Proceed and run the test configuration.
6. In order to reach ones maximum contraction, a resistance which works against the force of the muscle contraction is required. In many cases, a limb’s motion can restrained to produce a MVC.
7. Run and record any additional trials you may have.
8. Open EMGworks Analysis and import the MVC trial with all the runs you wish to normalize into a workspace.
9. Highlight the run(s) you wish to normalize in the Data window, located on the left side of the program.
10. Right-click within this window and navigate to Calculation Scripts → Amplitude Analysis.
11. In the parameter window, check off Normalize Data and select your normalizing series as the MVC trial.
    1. This EMGscript then performs an RMS computation on the input data and normalizes it against the peak RMS value of the MVC trial.
12. Select OK and the calculation will run in the background, appearing in the Data window when finished.
13. Plot the MVC normalization by selecting and right-clicking the series you wish to view. You have the options to plot these separately or as subplots.
    1. The output plots produced are displayed in %MVC versus time.
    2. MVC plots versus the corresponding raw EMG signals: