Two-Channel Electromyography (EMG) Application User Guide
Contents
- Introduction & launching the application
- Parameters
- Working with the Two-Channel EMG Application (User Interface)
- Report Functionality
Introduction
This guide introduces the Two-Channel EMG biofeedback application, part of the Mind-Body Training Tools suite. MBTT applications are designed to train self-regulation skills, which I sometimes call mind-body skills.
The guide has two purposes: firstly to give an overview of EMG biofeedback, and secondly to teach you how to use the software – though it is more of a reference than a tutorial.
Electromyography or EMG is an electrical correlate of muscle tension measured from the skin. Technically, it is a voltage measurement - voltage is measured between two active sensors that are attached to the skin (a third sensor, the “ground”, is also necessary). Broadly speaking, the tighter the muscles between and around about the two active sensors, the higher the EMG signal.
Thus the primary application of EMG biofeedback is in teaching relaxation skills. A secondary, or more specific application, is in teaching optimal breathing skills, since EMG biofeedback can be used to differentiate chest-based breathing from abdominal breathing.
Clearly, where to site the sensors plays a key role in EMG biofeedback.
This and other technical aspects of EMG biofeedback are covered in this guide.
The guide assumes that you already have a basic knowledge of how to work with Mind-Body Training Tools software. If not, I suggest you read this Introductory Guide to Working with MBTT.
The two-channel EMG app obviously differs from the basic EMG app in having two channels rather than one. One advantage is that you can compare left and right sides of the body, which can offer useful insights. Another application is to track the activity of two different muscles, for example the scalene muscles and the trapezius muscle, which are on the front and back side of the upper chest / lower neck, and can be active during breathing.
Launching The Application
To launch the application (after starting the platform program) first click on the "EMG & Peripheral" tab, then select the "EMG - 2 channel" application from the drop-down list, then click the button to launch the app.
Parameters
The 2-channel EMG has a single input parameter, EMG. As mentioned earlier, technical aspects of EMG and its measurement are given in this user guide. In this app EMG is measured from two different locations on the body.
EMG amplitude, averaged over a short period of time, is also the only feedback parameter.
Working With The Two-Channel EMG Application (User Interface)
The MBTT apps have a common design scheme. The intent is that learning to use one app, can be generalised so that other apps in the suite are easy to learn.
The apps generally have three windows:
- Main window, or trainer's window, containing parameter charts
- Threshold window - each app has at least one threshold, but there are usually more.
- Feedback window - in a sense, all charts and thresholds are giving feedback, but the feedback window contains controls for audio feedback plus more specialised feedback forms.
Main Window
The main screen looks like this:
TO_DO
Thresholds
In biofeedback, physiological parameters are mapped into visual or auditory form, so that the trainee can perceive changes directly through his senses. Feedback can be continuous and proportional to the parameter, for example a tone whose pitch and/or volume varies with the parameter, or it can be discrete and dichotomous, for example a bell sounds whenever muscle tension rises above some limit.
Thresholds are the means of configuring the mapping, meaning they define how much of the parameter results in how much feedback.
The principles of thresholding and feedback are described in greater detail in this guide.
The 2-channel EMG app has a two threshold, shown below.
The left side threshold is much the same as that in the Basic EMG app, except that it's parameter is the average of the two channels.
The right side threshold is different, its parameter is the difference between the two channels (channel 1 minus channel 2) and is designed to show differences between the left and right sides of the body. It has two levels, which can be updated “by hand” (by dragging with your mouse).
The EMG average threshold differs from most insofar as there is only one threshold level.
The simplest way to update the level is to drag it with your mouse, but there is also an option to have the software calculate a new level, based on a percentile, plus an offset either up or down, in microvolts (this being the unit of the EMG parameter).
You can thus for instance set the threshold level at the 25th percentile, plus an upward offset of 0.5 microvolts.
The reason for the difference is that EMG as a biofeedback parameter tends to vary in a particular way, that's different from other biofeedback parameters. Suppose you have your sensors on the forehead (which gives a general measure of tension in the face and head). What you often see in the EMG signal is periods of stability interspersed with movements or “fidgets” that produce sharp peaks in the signal that go much higher than the baseline, for example like this:
These peaks have the effect of raising the mean well above the natural “baseline”. So using the mean as a basis for calculating the threshold level, in practical terms, is less than ideal.
On the the other hand, you can get something that's much closer to the “baseline” by taking a percentile, perhaps the 20th.
Audio Feedback
The application offers midi feedback and threshold-based contingent audio feedback. Additionally, you can transmit feedback parameters out of BioEra, for use with external feedback applications. Please note that the Breath Player utility, which is part of the MBTT Platform program, cannot be used with the capnometry apps (except in breath pacer mode) because.
Threshold-Based Audio Feedback
To recap, the basic concept is that the software plays a sound (actually a midi note) whenever a threshold limit (level) is crossed.
The controls for threshold based feedback are found at the bottom of the threshold controls. There is a button to activate it / turn it off. A drop-down control sets the condition or contingency: for example if set to “above”, the feedback will sound whenever the parameter exceeds the upper level. “Below” means it sounds below the lower level, and “outside” means it sounds for either of these two.
You can change the midi “instrument”, and you can have the sound repeat for each breath that meets the threshold condition, or only the first time the level is crossed.
Audio Feedback Window
The controls for audio feedback, aside from the threshold-based audio feedback discussed above, are found in a separate window shown below:
In midi feedback, a musical note is played whose pitch varies with the selected feedback parameter. You can select which parameter to use as the basis of feedback using a drop-down list control, and you can invert the pitch mapping if you wish, so that a higher reading produces a lower tone.
Tone feedback works in the same way as midi feedback, except that a simple, constant tone is played in place of midi notes. Tone feedback could be said to have greater sensitivity, since the pitch varies continuously rather than being restricted to musical pitches (A, B, C# etc.) as midi feedback does.
Audio feedback is demonstrated in the following video TO_DO.
Report Functionality
Mind-Body Training Tools allows you to generate session reports and application reports.
The controls for report generation are found in the platform window, in the EMG & Peripheral tab shown towards the beginning of this document. You need to have selected the right application from the drop-down list - in this case EMG 2-channel.
A session report shows charts and tables for the feedback parameters summarising the whole session. You'll be asked to select one particular session, and given report options. The options dialog looks like this:
The application report shows the variation of the feedback parameters across multiple sessions. Typically for each feedback parameter, the software generates line charts for session means, session maxima and session minima.
Report functionality is described in greater depth here.
You can see sample reports here:
Sample Session Report from the EMG, GSR and Skin Temperature application
Sample Application Report (not the 2-channel EMG application).