USE3 Physiolab Software Guide - J&J Engineering Biofeedback ...

Physiolab Software Guide 46
EMG Displays
A “W” specified before a screen name in the Select Screen Bar indicates that a
wide bandpass filter (20-400Hz) has been applied to EMG signals displayed in
that screen. The wide bandpass filter eliminates artifact frequencies outside of
the EMG range. If no “W” appears before a screen name, an additional narrow
band filter (100-400 Hz) has been applied to EMG displays on that screen. This
narrow band filter eliminates heart artifact from the EMG signal. Within the
display, narrow band EMG signals will be labeled with an “N”. For example,
FFT_EMG A N or EMG-B RMS N. The A or B refers to the input receiving the
EMG signal. Wide band EMG signals are labeled within displays with a “W” as
follows: EMG-B W or EMG-A RMS W.
The signal is then passed through a 50 or 60 Hz notch filter to eliminate power
line artifact. (For more information please see “Eliminating Electrical Line
Frequency Noise” in the “Configuring the Software” section.
Unless the screen is labeled “Raw” or “FFT” it contains EMG RMS (Root Mean
Square) signals. Most EMG biofeedback screens display EMG RMS signals.
EMG RMS screens are defaulted to AutoOffset ON so that the Signal Up/Down
buttons are disabled. This is because evaluating the signal in relation to zero is
essential to EMG RMS measurements. Moving the signal up so that the zero is
no longer visible on the scale would not be desirable for this display.
W-EMG Displays
The following display descriptions apply to both wide band and narrow band
EMG displays. The screen choices are identical, but a filter to eliminate heart
artifact has been applied to the signals in the narrow band screens. Wide band
displays show a greater degree of muscle activity so normally you will want to
use wide band displays unless the site you are monitoring is contaminated by
heart muscle artifact. Narrow electrode muscle placement and placement far
from the heart will have less artifact than wide placement and electrode sites
close to the heart. You can determine if heart artifact is a problem if there is an
observable R-wave point in a raw EMG display and/or a rhythmic pulsing in the
100-400 Hz range of an EMG FFT display. If heart artifact is present, use the
screens without the “W” designation (the narrow bandpass screens).
Single Signal Displays
The following EMG displays contain only one signal per line graph space:
Raw EMG
A line graph display with vertical microvolt scale and horizontal time scale, which
provides a very fast response display of raw EMG activity. Because this display
responds very fast to very small movements, it is useful for EMG activity that is