2. Introduction
• Electromyography (EMG)measures muscle
response or electrical activity in response to a
nerve's stimulation of the muscle.
• Electromyography is the study of motor unit
activity.
• In electromyography, the study of the electrical
activity of contracting muscle provides information
concerning the structure and function of motor
unit.
3. • It is a technique by which the action potential of
the contracting muscle fiber and motor units are
recorded and displayed.
• This test is used to help detect neuromuscular
abnormalities.
4. Recording of EMG
Recording the EMG requires a 3 phase system-
1. Input phase - It includes electrodes to pick up
electrical potential from contracting muscle.
2. Processor phase - It amplifies the very small
electrical potential.
3. Output phase - It includes the display and
analysis of electrical potential by visual and auditory
means.
5. Type of electomyography
• (a) Diagnostic/ clinical EMG - It is used for study of
disease of muscle , neuromuscular junction and
nerves.
• (b) Kinesiological EMG - It is used for study of
muscle activity.
7. Electrodes
• An electrode is a transducer.
• It can be monopolar / bipolar.
• Surface electrode can be sliver / sliver chloride
coated.
• Needle electrode consists of insulated fine wire
saved for 1-2mm at tip which are inserted into the
chosen muscle.
8. • In monopolar technique, the recording electrode is
either placed over the muscle belly or inserted into
the muscle.
• Second electrode called the reference electrode is
placed over the skin near the site of insertion of
muscle.
• Third electrode called ground electrode apply near
the recording electrode, but not over the muscle.
9. • In bipolar arrangement, the 2 electrode are placed
over the muscle belly in a longitudinal direction
parallel to muscle fibre or the 2 wire threaded
through the cannula are inserted into the muscle.
• In bipolar needle electrode placing, the needle
electrode act as ground, so no separate grounding
is required.
10. Amplifier system
• Before the motor unit can be visualised, it is necessary to
amplify small myoelectric signals. Amplifier converts electric
signals large enough to be displaced.
• Differential amplifier - control unwanted part of signal.
• Common mode rejection ratio - measure of how much
desired signal voltage is amplified relations to unwanted
signal.
• Input impedance - Impedance is present at input of
amplifier and as well as the output of electrodes and they
are directly related to voltage.
11. Display devices
• After the signal is processed and amplified, it is
displayed on a cathode ray oscilloscope.
• Cathode ray oscilloscope consists of electrode gun
screen , and vertical plates.
• Tape recorder used to store EMG information.
• Loudspeaker used to listen the signal.
• Computer used which perform complex analysis
and send results to printer.
