Electromyogram

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. M easured 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

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