Biomedical Engineering Reference
In-Depth Information
3 mv
Raw EMG
BIOAMP.
3 mv
Full Wave
Rectify
1 mv
L. P. Filer
Linear
Envelope
1 mv. s
Integrate
Over Contr.
50
m
v. s
Integrate 50ms
Then Reset
Integrate To
Present Voltage
Then Reset
Each Pulse = 38
m
v.s
Figure 10.15 Schematic diagram of several common EMG processing systems and
the results of simultaneous processing of EMG through these systems. See the text for
details.
10.3.1 Full-Wave Rectification
The full-wave rectifier generates the absolute value of the EMG, usually with
a positive polarity. The original raw EMG has a mean value of zero because
it is recorded with a biological amplifier with a low-frequency cutoff around
10 Hz. However, the full-wave rectified signal does not cross through zero
and, therefore, has an average or bias level that fluctuates with the strength
of the muscle contraction. The quantitative use of the full-wave rectified
signal by itself is somewhat limited; it serves as an input to the other pro-
cessing schemes. The main application of the full-wave rectified signal is in
semi-quantitative assessments of the phasic activity of various muscle groups.
A visual examination of the amplitude changes of the full-wave rectified sig-
nal gives a good indication of the changing contraction level of the muscle.
The proper unit for the amplitude of the rectified signal is the millivolt, the
same as for the original EMG.
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