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EMG Analyzer

The EMG Signal preprocesses an EMG signal and performs standard epoch-based analyses.


Table of contents
  1. Introduction
  2. User Corrections
  3. Settings
  4. Metrics
  5. References

Introduction

The EMG Signal Analyzer filters a raw EMG signal, then rectifies and smooths it to obtain a smooth continuous representation of muscle activity. The module features two types of configurable EMG smoothing filters: a boxcar filter and a low pass filter. The default settings are based on A. van Boxtel (2010)1, which tested the efficacy of various filters when applied to blink reflex research.

If artifacts are present, the module allows users to remove sections from the smooth signal, which are then interpolated over.

EMG Analyzer
Figure 1: The EMG Signal Analyzer interface.

User Corrections

The EMG Signal Analyzer allows the user to define zones in which the smooth EMG signal is not used, but is instead interpolated over. This is similar to the process described in the Generic Signal Analyzer module, but does not affect the raw signal, only the smooth EMG signal.


Settings

The EMG signal analyzer assumes that the unit of the EMG signal is mV. If this is not the case, fill in an appropriate gain value (multiplier) to transform the raw signal into mV; e.g., if the signal is in V, the gain should be 1000.

The EMG Analyzer additionally features a notch filter (iirnotch with Q = 35) that can be used to filter out line noise.

The auto-generated list below shows the settings available in the EMG Analyzer module:

  • General Settings:
    Name, source and epoch settings for this EMG PhysioAnalyzer.

    • Analyzer prefix (tag):
      The tag (name) of this PhysioAnalyzer. The tag must be unique and start with a letter, and may only contain alphanumeric characters.

    • Channel-number of signal:
      The channel number (index) of the signal to be analyzed.

    • Generate epochs from:
      Specifies how epochs are generated.

  • Preprocessing Settings:
    Settings for prefiltering the raw EMG signal. The signal unit must be mV, if it is not, use a gain multiplier to transform it.

    • Gain (signal multiplier) [x]:
      The gain is the value with which the raw signal is multiplied before being further processed and analyzed.

    • High-pass FIR filter [Hz]:
      The high-pass filter and its cutoff frequency.

    • Low-pass FIR filter [Hz]:
      The low-pass filter and its cutoff frequency.

    • Notch filter [Hz]:
      The notch filter and its cutoff frequency.

  • Smoothing Settings:
    The rectified EMG signal can be smoothed using either a Boxcar filter (window size of 100 ms recommended) or a lowpass 201 coeff. FIR filter (frequency of 5 or 10 Hz recommended).

    • Smoothing filter type:
      The filter type to use for smoothing the filtered and rectified EMG signal.

    • Boxcar-size or filter-frequency [ms or Hz]:
      The window size of the smoothing boxcar filter or the low-pass cutoff freqeuncy of the smoothing FIR filter; depending on what was selected.


Metrics

The auto-generated table below lists all the metrics produced by the EMG Analyzer module.

Table 1: The metrics calculated by the EMG Analyzer module.

Variable: Unit: Description:
Min_Smooth_EMG mV The minimum value of the filtered, rectified and smoothed EMG signal, per epoch.
Max_Smooth_EMG mV The maximum value of the filtered, rectified and smoothed EMG signal, per epoch.
Mean_Smooth_EMG mV The mean value of the filtered, rectified and smoothed EMG signal, per epoch.
BoundedArea_Smooth_EMG mV/s The area bounded by the filtered, rectified and smoothed EMG signal and the abscissa, per epoch.
TimeToMax_Smooth_EMG s The time between the start of the epoch and the point where the filtered, rectified and smoothed EMG signal reaches its maximum point in that epoch.
Min_Filt_EMG mV The minimum value of the filtered EMG signal, per epoch.
Max_Filt_EMG mV The maximum value of the filtered EMG signal, per epoch.
Mean_Filt_EMG mV The mean value of the filtered EMG signal, per epoch.
Min_FiltRect_EMG mV The minimum value of the filtered and rectified EMG signal, per epoch.
Max_FiltRect_EMG mV The maximum value of the filtered and rectified EMG signal, per epoch.
Mean_FiltRect_EMG mV The mean value of the filtered and rectified EMG signal, per epoch.
Interpolated_Smooth_EMG % The percentage of the epoch in which the user chose to interpolate the smooth signal; i.e. the size inside the epoch of the smooth signal section(s) that were interpolated over, relative to epoch size.

References

  1. Van Boxtel, A. (2010). Filter for optimal smoothing of acoustic and electric blink reflex EMG responses to determine blink response magnitude. Biological Psychology, 85, 299-305. 


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