EMG - SPECTRAL MEAN / MEDIAN FREQUENCY
Spectrtal EMG shows the distribution of energy by frequency at rest and during work.
SPECTRAL MUSCLE sEMG SIGNALS:
2D FFT EMG
A two-dimensional fill graph on showing the frequency distribution of the EMG signal uses a Fast Fourier Transform calculation similar to that for EEG FFTs. The bottom scale represents frequency in Hz and the vertical scale represents amplitude.
2D FFT sEMGs are useful for showing immediate frequency changes. The display on the left shows a normal FFT signal, while the one on the right shows how effective this display is for revealing electrical line frequency signal contamination, which appears as regular 50 Hz or 60 Hz spikes within the display. (For more information, see “Artifact Detection” in your Hardware Guide.)
3D FFT EMG
Same as above but shown in 3-D with a third axis representing units of time. This display is particularly useful for highlighting even small frequency variations over time. This display is processor intensive and should be avoided if you have a slow computer.
Mean-Median (m-m) sEMG Frequency Signals:
J&Js sEMG system detects the full spectral EMG signal in Wide-filter applications. This allows specialty applications that detect the EMG spectrum and abstract two spectral signals, the spectral mean sEMG frequency, and the spectral median sEMG frequency. These mean and median signals can be placed on line graphs and bar graphs. These graphs allow a rapid and precise way of evaluating the skewness of the spectral sEMG FFTs. Here is an example.
The computer detects the mean and median frequency in the raw spectral EMG signal. It converts the mean and median to line graph signals, like this:
Here is the final result: The mean and median are shown as a combined band - the narrower the band the closer the mean is to the median.
EMG amplitude is on the top. Mean-median frequency is in the middle, and the amount of skewness is on the bottom.
As amplitude varies, so does the spectral mean and median. Color points indicate brief periods where the muscle expressed a reversal of normal skewness; the mean was above the median frequency for a moment, suggestive of local muscle fatigue. This reversal of skewness is also shown on the bottom graph, as periods where the color bar drops out.
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| Underlying spectral plot |
Underlying spectral plot flattened |
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| Resulting mean freq/median freq. plot |
mean median emg line |
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| emg_spetral_all |
SPECTRAL MUSCLE sEMG SIGNALS:
2D FFT EMG
A two-dimensional fill graph on showing the frequency distribution of the EMG signal uses a Fast Fourier Transform calculation similar to that for EEG FFTs. The bottom scale represents frequency in Hz and the vertical scale represents amplitude.
2D FFT sEMGs are useful for showing immediate frequency changes. The display on the left shows a normal FFT signal, while the one on the right shows how effective this display is for revealing electrical line frequency signal contamination, which appears as regular 50 Hz or 60 Hz spikes within the display. (For more information, see “Artifact Detection” in your Hardware Guide.)
3D FFT EMG
Same as above but shown in 3-D with a third axis representing units of time. This display is particularly useful for highlighting even small frequency variations over time. This display is processor intensive and should be avoided if you have a slow computer.
Mean-Median (m-m) sEMG Frequency Signals:
J&Js sEMG system detects the full spectral EMG signal in Wide-filter applications. This allows specialty applications that detect the EMG spectrum and abstract two spectral signals, the spectral mean sEMG frequency, and the spectral median sEMG frequency. These mean and median signals can be placed on line graphs and bar graphs. These graphs allow a rapid and precise way of evaluating the skewness of the spectral sEMG FFTs. Here is an example.
The computer detects the mean and median frequency in the raw spectral EMG signal. It converts the mean and median to line graph signals, like this:
Here is the final result: The mean and median are shown as a combined band - the narrower the band the closer the mean is to the median.
EMG amplitude is on the top. Mean-median frequency is in the middle, and the amount of skewness is on the bottom.
As amplitude varies, so does the spectral mean and median. Color points indicate brief periods where the muscle expressed a reversal of normal skewness; the mean was above the median frequency for a moment, suggestive of local muscle fatigue. This reversal of skewness is also shown on the bottom graph, as periods where the color bar drops out.
|
|
|
| Underlying spectral plot |
Underlying spectral plot flattened |
|
|
|
| Resulting mean freq/median freq. plot |
mean median emg line |
|
|
| emg_spetral_all |