Biomedical Engineering Reference
In-Depth Information
first attempt at developing recommended standards was done by the Interna-
tional Society of Electrophysiological Kinesiology, which resulted in an Ad
Hoc Committee Report (Winter et al., 1980). More recently, a considerably
more in-depth report was published with the support of the European Union
and was called SENIAM (Surface EMG for a Non-Invasive Assessment of
Muscles). During 1996 - 1999, the report was developed and reviewed by over
100 laboratories (Hermens et al., 2000), and the final report was published as
a booklet and as a CD-ROM: SENIAM 8: European Recommendations for
Surface Electromyography, 1999.
The SENIAM recommendations as to information to be reported are as
follows:
1. Electrode size, shape (square, circular, etc.), and material (Ag, AgCl,
Ag/AgCl, etc.)
2. Electrode type (monopolar, bipolar, one- or two-dimensional array)
3. Skin preparation, interelectrode distance
4. Position and orientation on the muscle (recommendations for 27 mus-
cles are included)
10.3
PROCESSING OF THE ELECTROMYOGRAM
Once the EMG signal has been amplified, it can be processed for comparison
or correlation with other physiological or biomechanical signals. The need
for changing the EMG into another processed form is caused by the fact that
the raw EMG may not be suitable for recording or correlation. For example,
because of the higher frequencies present in the EMG, it is impossible to
record it directly on a pen recorder. The frequency response of most recorders
(0 - 60 Hz) means that most of the higher frequency components of the EMG
are not seen.
The more common types of online processing are:
1. Half- or full-wave rectification (the latter also called absolute value)
2. Linear envelope detector (half- or full-wave rectifier followed by a
low-pass filter)
3. Integration of the full-wave rectified signal over the entire period of
muscle contraction
4. Integration of the full-wave rectified signal for a fixed time, reset to
zero, then integration cycle repeated
5. Integration of the full-wave rectified signal to a preset level, reset to
zero, then integration repeated
These various processing methods are shown schematically in
Figure 10.15, together with a sample record of a typical EMG processed all
five ways. This is now discussed in detail.
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