presentation for electromyogram

1. Electromyogram
(EMG)
Jhoniel Viloria

2. Introduction
 Electromyogram (EMG) is a technique for evaluating
and recording the activation signal of muscles.
 EMG is performed by an electromyograph, which
records an electromyogram.
 Electromyograph detects the electrical potential
generated by muscle cells when these cells contract
and relax.

3. Introduction
 Electrical signals associated with the contraction of a
muscular is called an electromyogram (EMG).
 The study of EMG’s is called electromyography.

4. History
 1838 – Matteucci first describes the existence of
electrical output from muscle.
 1929 – introduction to coaxial needle electrode
 It has been noted that the relaxing muscle doesn’t
produce voltage, the EMG signals are generated in
case of muscle contractions.

5. EMG Signal
Factors, which can influence the EMG signal:
 Velocity of shortening or lengthening of the muscle
 Fatigue;
 Reflex activity.

6.  Muscle Signals are
Analog in nature.
 EMG signals are also
collected over a
specific period of time.
Analog Signal
EMG Signal

7. Electrical Characteristics
 The electrical source is the muscle membrane potential
of about -70mV.
 Measured EMG potentials range between < 50 μV up to
20 to 30 mV, depending on the muscle under
observation.
 Typical repetition rate of muscle unit firing is about
7-20 Hz.

8. Power Spectrum
Frequency (Hz)

9. EMG PROCEDURE
 Clean the site of application
of electrode;
 Insert needle/place surface
electrodes at muscle belly;
 Record muscle activity at rest;
 Record muscle activity upon
voluntary contraction of the
muscle.

10. EMG Circuit

11. EMG Circuit

12. Amplification
& Filtering
Signal pick up
Conversion of Analog
signals to Digital signals
Computer
EMG Processing

13. Applications of EMG
 EMG can be used for diagnosis of Neurogenic or
Myogenic Diseases.
 Indicator for muscle activation/deactivation
 Relationship of force/EMG signal
 Use of EMG signal as a fatigue index

14. Types of EMG
Electrode Categories
Inserted
Fine-wire (Intra-muscular)
Needle
Surface

15. Intramuscular
- Needle Electrodes
Extramuscular
- Surface Electrodes
Types of EMG

16. Fine-wire Electrodes
Advantages
Extremely sensitive
Record single muscle activity
Access to deep musculature
Little cross-talk concern
Disadvantages
Extremely sensitive
Requires medical personnel, certification
Repositioning nearly impossible
Detection area may not be representative of entire muscle

17. Surface Electrodes
Advantages
Quick, easy to apply
No medical supervision, required certification
Minimal discomfort
Disadvantages
Generally used only for superficial muscles
Cross-talk concerns
No standard electrode placement
May affect movement patterns of subject
Limitations with recording dynamic muscle activity

18. General Concerns
Signal-to-noise ratio
Ratio of energy of EMG signal divided by energy of
noise signal
Distortion of the signal
EMG signal should be altered as minimally as possible
for accurate representation

19. Characteristics of EMG Signal
 Amplitude range:
0–10 mV (+5 to -5)
prior to
amplification
 Useable energy:
Range of 0 - 500 Hz
 Dominant energy:
30 – 200 Hz

20. Characteristics of Electrical Noise
 Inherent noise in electronics equipment
 Ambient noise
 Motion artifact
 Inherent instability of signal

21. Inherent Noise in Electronics Equipment
 Generated by all electronics equipment
 Frequency range: 0 – several thousand Hz
 Cannot be eliminated
 Reduced by using high quality components

22. Ambient Noise
 Electromagnetic radiation sources
Radio transmission
Electrical wires
Fluorescent lights
 Dominant frequency: 60 Hz
 Amplitude: 1 – 3x EMG signal
 Essentially impossible to avoid

23. Motion Artifact
 Two main sources
Electrode/skin interface
Electrode cable
 Frequency range: 0 – 20 Hz
 Reducible by proper circuitry and set-up

24. Inherent Instability of Signal
 Amplitude is somewhat random in nature
 Frequency range of 0 – 20 Hz is especially unstable
 Therefore, removal of this range is recommended

25. Maximizing Quality of EMG Signal
Signal-to-noise ratio
Highest amount of information from EMG signal as
possible
Minimum amount of noise contamination
As minimal distortion of EMG signal as possible
No unnecessary filtering
No distortion of signal peaks
No notch filters recommended
Ex: 60 Hz

26. End
of
Slide Show