brief description of Electromyography

1. ELECTROMYOGRAPHY(EMG)
By Sunil

3. In mid-1600s, when Francesco Redi, documented that a highly specialized
muscle was the source of the electric ray fish’s energy
1773, Walsh had been able to demonstrate clearly that the eel’s muscle tissue
could generate a spark of electricity

4. It was not until the 1790s that Galvani obtained direct evidence of the
relationship between muscle contraction and electricity.
He demonstrated that muscle contractions could be evoked by the discharge
of static electricity.
In 1792, Volta initially agreed; he later concluded that the phenomenon
Galvani had seen did not emanate from the tissue itself, but rather was an
artifact of the dissimilar metals touching the muscle tissue.

5. Electrodiagnostic studies
Electrodiagnostic studies originated in the 19th century but have only been
consistently used within the past 30–40 years.
1773, Walsh had been able to demonstrate clearly that the eel’s muscle tissue
could generate a spark of electricity
1790s that Galvani obtained direct evidence of the relationship between
muscle contraction and electricity; he conducted a series of studies that
demonstrated that muscle contractions could be evoked by the discharge of
static electricity.

6. Galvani try to get evidence Volta’s criticism and was able to demonstrate the
firing of the muscle by contracting it with a severed nerve rather than metal.
This finding, however, went unnoticed for four decades because of Volta’s
popularity
Volta had developed a powerful tool that could be used both to generate
electricity and to stimulate muscle.
The technique of using electricity to stimulate muscles gained wide attention
during the nineteenth century,

7. In 1838, Matteucci used the galvanometer to demonstrate an electrical
potential between an excised frog’s nerve and its damaged muscle
By 1849, Du Bois- Reymond provided the first evidence of electrical activity
in human muscles during voluntary contraction.

8. During the 1960s, the technique of biofeedback
was born.
Basmajian’s work on single motor unit training
provided some of the impetus for research on
biofeedback

9. Surface EMG recordings provide a safe, easy, and noninvasive method that
allows objective quantification of the energy of the muscle.
It is not necessary to penetrate the skin and record from single motor units to
obtain useful and meaningful information regarding muscles.
The technique allows the observer to see the muscle energy at rest and
changing continuously over the course of a movement.
With the use of multiple sensor arrays, it becomes possible to differentiate how
different aspects of muscles do different things.

10. By using SEMG, we are able to answer the following questions:
Do the muscles fire early or late in a recruitment pattern?
Does a particular exercise actually activate the muscle it is intended to, or
is a substitution pattern present?
Does the muscle turn off following a given movement, or does it show
irritability following movement?

11. Limitations
One key limitation is our ability to monitor only a few muscle sites.
The neuromuscular system is very rich and complex, and to reduce it to one
or two channels of SEMG information is very limiting
Another difficulty with SEMG is the possibility of “crosstalk,” a phenomenon
where energy from one muscle group travels over into the recording field of
another muscle group.

12. SEMG is not a measure of force, nor is it a measure of strength, or of the
amount of effort given, or of muscle resting length.
It is simply a measure of the electrical activity given off by the muscle.

13. Anatomy and Physiology

18. General guidelines
● Wet gel electrodes have the best skin impedance values
● Use small electrodes to increase the selectivity of your measures
(avoid cross-talk)
● The smaller the electrode (active detection area) the higher the
impedance values
● Select the closest possible inter-electrode distance to increase
selectivity
● The general recommendation for the inter-electrode distance is 2 cm
(center point to center point)

19. ● Apply electrodes in parallel to the muscle fiber direction
● Use the most dominant middle portion of the muscle belly for best
electivity
● Avoid the region of motor points if possible (see next page)
● Take care that the electrode site remains on the active muscle mass
during muscle shortening
● Use a map system with measured distances between the electrode
site and dominant anatomical landmarks

23. Skin preparation procedures
1) Removing the hair: This is needed to improve the adhesion of the
electrodes, especially under humid conditions or for sweaty skin types and/or
dynamic movement conditions.
2) Cleaning of the skin:

24. Skin surface electrodes
Commercial disposable electrodes are manufactured as wet gel electrodes or
adhesive gel electrodes.
Use small electrodes to increase the selectivity of your measures (avoid
cross-talk)
The general recommendation for the inter-electrode distance is 2 cm (center
point to center point)

25. Electrodes material,size
Surface electrodes are usually made of silver/silver chloride (Ag/ AgCl), silver
chloride (AgCl), silver (Ag) or gold (Au)

26. Lead and cable connections

28. Factors influencing the EMG signal
1) Tissue characteristics: electrical conductivity varies with tissue type,
thickness , physiological changes and temperature.
2) Physiological cross talk: Neighboring muscles may produce a significant
amount of EMG that is detected by the local electrode site.
3) Changes in the geometry between muscle belly and electrode Site Any
change of distance between signal origin and detection site will alter the EMG
reading.

29. 4.) External noise: Special care must be taken in very noisy electrical
environments
5) Electrode and amplifiers:

30. The energy that is generated by the muscle has a very small value and is
measured in millionths of a volt (microvolts).
It is necessary to use very sophisticated and sensitive instruments to amplify
this signal so that it can be seen and heard

31. FILTERING THE ELECTROMYOGRAPHIC SIGNAL
The first level of processing is known as filtering.
Most SEMG instruments contain a 60-Hz notch filter.
This filter may be found in the electronic circuitry of the SEMG instrument (an
analog filter) or in the software it uses (a digital filter).
it rejects (does not let through) any energy that is between 59 and 61 Hz

32. The next essential filter for SEMG is the band passfilter.
This filter passes on only a certain frequency range of energy for further
quantification and display.
For example, a typical band pass filter might let through all of the energy
above 20 Hz and then close the gate at 300 Hz

33. Selecting the filters for SEMG recordings is something of an art, because
certain filters are better for some applications than others.
For example, for SEMG recordings from the face, a 25- to 500-Hz band pass
filter is preferable because the muscles of the face readily emitfrequencies up
to the 500-Hz range

34. The energy from muscles has a frequency spectrum

35. Raw Surface Electromyography Display
The raw SEMG display is the oldest form of SEMG presentation.
It presents an unprocessed, peak-to-peak oscilloscopicdisplay of the SEMG
signal.

37. SEMG signal oscillates in both the positive and negative directions, and also
varies in its thickness and height.
The stronger the SEMG signal and the stronger the contraction

38. The Processed Signal
For example, this processing may be done either electronically by the
resistors, capacitors, and integrated circuits (ICs) that follow the amplifier or
digitally by computer software.
The processing of the signal may result in a variety of quantities (e.g., RMS,
integral average),

39. QUANTIFICATION OF THE SURFACE
ELECTROMYOGRAPHIC SIGNAL
All of the positive values would cancel out all of the negativevalues, and the
resulting sum would be zero.
For this eason, there are three ways in which SEMG values are commonly
derived: peak to peak, integral averaging, and RMS
Peak to peak is used in raw SEMG recordings
Usually the peak-to-peak measurement is summed and averaged over a
period of time

40. Peak-to eak values in a normal resting muscle might range between 2 and 10
microvolts
Integral average (μv/sec) is used with the processed SEMG signals.

42. RECORDING AND TAKING OUTPUT FROM EMG
STEP 1
calibration of machines

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