Electromyography (EMG) is a technique for recording electrical activity produced by skeletal muscles using an electromyograph. It assesses muscle activation through the detection of action potentials, characterized by various features such as duration, amplitude, and number of phases. EMG analysis can be qualitative or quantitative, and factors affecting muscle unit potentials (MUP) include technical and physiological aspects.

1. ELECTROMYOGRAPHY
©2020 Rohit Bhaskar PT
1

2. • Electromyography (EMG)
– is a technique for evaluating & recording the electrical
activity produced by skeletal muscles
– is performed using an instrument called an electromyograph,
to produce a record called an electromyogram
• a resting muscle does not show recordable electrical
potential but with increase force of contraction,
amplitude of potential increases
• an electromyograph detects electrical
potential generated by muscle cells when
these cells are electrically or neurologically
activated
©2020 Rohit Bhaskar PT
2

3. Equipment
• electrodes
– Surface electrodes
– Needle electrodes
• a high-gain amplifier (10-5000Hz)
– connected to an oscilloscope
• oscilloscopic traces may be photographed or stored on magnetic tape
– EMG signals may be fed to an audio unit for an on the spot feel of the
signals
• an arrangement for recording the output
– EMG is best done in a specially constructed shielded room to
prevent interference
3

4. • the sum of the action potentials produced in
the muscle
• characterized by its duration, number of
phases, amplitude, & rate of rise of first
component
©2020 Rohit Bhaskar PT
4
Motor unit potential (MUP)

5. Feature of MUP
Duration • measured from the initial take-off to the
point of return to the baseline
• 5-15 ms
Phases • portion of the MUP between the
departure & the return to the baseline
• triphasic (positive, negative, positive)
• Polyphasic-MUP with more than four phase (5-
15%)
Amplitud
e
• measured from maximum peak of negative
phase to maximum peak of the positive
phase
• 0.5mV to 2mV
Rise time • duration from the initial positive to
subsequent negative peak
• normal ↓ 500 µs
©2020 Rohit Bhaskar PT
5

6. Factors that effect MUP
• Technical factors
– Type of needle electrode
– Characteristics of recording surface
– Electrical characteristics of cable
– Preamplifier & amplifier
– Method of recording
• Physiological factors
– Age of the patient
– Muscle examined
– Temperature
6

7. Analysis of EMG
• Qualitative analysis
– visual inspection of the record
• Quantitative analysis
– amplitude, duration, & frequency
– power spectrum analysis
©2020 Rohit Bhaskar PT
7

8. Fibrillation Fasciculation
contraction of
individual muscle fiber
contraction of
individual motor units
cannot be seen through
the skin
visible through the skin
when muscle fibers lose
contact with their
innervating axon
occurs as a result of
additional nerve
impulses generated
10-100 µV in amplitude, 1-2
ms in duration, & 10 Hz in
frequency
50-500 µV in amplitude, 2-4
ms in duration, & 2-20 Hz in
frequency
Neuropathy, myopathy Neuropathy
©2020 Rohit Bhaskar PT
8

9. Thank You
©2020 Rohit Bhaskar PT
9