EMG -WIDE / NARROW BANDS
Surface EMG (sEMG) is a non-invasive way of detecting neuomuscular activity under the skin. Early sEMG biofeedback devises were very noisy. Developers discovered they could reduce noise by restricting sEMG bandwidths from the research-grade wide bandwith of 20 to 400 Hz to a more restriced narrow bandwidth of 100 to 200 Hz. These became known as Wide and Narrow (band) EMG.This applies to all muscles, including those on the Pelvic Floor.
Triple Electrode Cable with Ground - MC-5SGW FOR EMG
Electrode Cable with ground (green) and two standard snaps (positive and negative) for EMG.
Use this cable if you are not attaching the skin conductance. The green skin conductance sensor is also a system and ground.
Dual Electrode Cable -no Ground - MC-5SW FOR EMG
use this censor cable for all EMTs. After you have connected a ground.
WIDE vs NARROW EMG SIGNALS:
Today J&J equipment is so stable that it detects wide sEMG accurately, without noise issues. The new J&J USE3 Plus Bundled and Advanced EMG Applications use only Wide Band EMG. The reason is simple - J&J has added spectral sEMG signal detection, and spectral sEMG demands a wide band. If you get ECG 'spikes' you can still do feedback by placing the Thresholds at the lowest point of the EMG wave.
We do however have some early [pre-2007] EMG applications using Narrow band sEMG. The only remaining reason to continue with narrow-band sEMG is to reduce the effect of ECG 'spikes' on sEMG signals. Any time an electrode pair crosses from the left to the right side of the body, ECG will be detected. The ECG signal is very large comared to relaxed sEMG, so it bleeds through even though the bandwidth for ECG is very low. It is still high enough to be detected as part of the wide sEMG signal. The solution for ECG-'contaminaed' EMG is to either accept it or try narrow band signals.
A “W” is sometimes specified before a screen name in the Select Screen Window. Sometimes a 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 a " N” 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”.
The signal, narrow or wide, is always 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.
Why Narrow Band? To reduce ECG spikes in some EMG placements.
Wide band signals 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 narrow bandpass screens.
* Unless the screen is labeled “Raw” or “FFT” it contains EMG RMS (Root Mean Square) signals by default.
* The RMS EMG signal is the most used EMG signal type for myofeedback and neuromuscular rehabilitation. Most EMG biofeedback screens display EMG RMS signals.
* NOTE: The MyoPilot application uses Wide band sEMG by default. The 'W' designation is not used to simplify screen signal names.
NOTE: Be sure you have the subject connected to a ground (green) lead on another sensor. Grounds are found on two sensors, the MC-5SGW [above], and the MC-6S-Y Green Skin Conductance lead. Use either or both.
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EMG FEEDBACK [MyoFeedback]: This signal varies directly with muscle tension, posture and placement. Any EMG placement that crosses the mid-line will show an ECG-derived heart pulse as well.
SHAPING: Manually adjust the threshold using the THR ADJ Buttons on the lower right to shape the signal higher or lower. Take a baseline reading, then adjust threshold for feedback.
SCALE: To see the signal, adjust the SCALE.
AVR: To smooth the signal, adjust the AVERAGE.
ALL ACTIVES LOCKED: Wen the EMG signal succes at the threshold [for 0.25 sec], this completes a success cycle and triggers fedback. It also advances the red ACTIVES ON TARGET one unit.
A LAP is completed when 10 ACTIVES ON TARGET units were completed.
AUTO-THESHOLD is Off: Since the signal has a zero-point, there is no need for auto-thresholding.
ABOVE T./ BELOW T. :
Below T.: A tone will signal successful feedback whenever the signal drops below the current threshold value for 0.25 sec.
To change this, toggle to Above T.
Above T.: A tone will now signal successful feedback whenever the signal rises above the current threshold value for 0.5 sec.
TYPE OF FEEDBACK: This type of feedback is Absolute Signal Feedback. It provides information about the absolute value of the signal.