In the name of God

1. In the name of God Electromyography (EMG) By:sahar shahbazi

2. What is EMG? EMG stands for electromyography. It is the study of muscle electrical signals. EMG is sometimes referred to as myoelectric activity. Muscle tissue conducts electrical potentials similar to the way nerves do and the name given to these electrical signals is the muscle action potential.

3. What is motor unit? • The smallest subunit that can be controlled is called motor subunit because it is separately innervated by a motor axon. • The number of the muscle fibers that are under control of 1 motor unit varies from 3 to 20,000 depending on the fineness of the control required.

4. Samples of EMG signal • An EMG signal is the train of Motor Unit Action Potential (MUAP) showing the muscle response to neural stimulation.

5. In response to a stimulus from the neuron, a muscle fiber depolarizes as the signal propagates along its surface and the fiber twitches. This depolarization, accompanied by a movement of ions, generates an electric field near each muscle fiber.

7. Motor unit

8. EMG Applications • Indicator for muscle activation/deactivation • Relationship of force/EMG signal • Use of EMG signal as a fatigue index • Chronic pain study

9. Signal processing and amplification

10. 1. rectification • 2. Filtering and linear envelope detection • 3. Integration • 4. Amplification : • Amplifier impedance • common mode rejection

11. Outcome measures: • horizontal axis (time) • timing (percent on/off; on/off ratio)duration (sec; percent of cycle)coactivation (percent of cycle)Area under the curve (related to force) • vertical axis (voltage) • rate of rise of voltagepeak amplitude

12. Ellaway's cumulative sum histogram technique: Where Si is the cumulative sum up to sample i, X is the mean voltage over the trial, and xi is the voltage at sample

13. The measurement of EMG

14. When the muscle is activated, the length of the muscle decreases and the muscle, skin and electrodes will be moving with respect to each other. The electrode signal will therefore probably show some movement artifacts. • This is not the only difficulty when measuring an EMG. When the muscle is moving, the body will show some movements as well, and the cable may move in the space between the electrode and the input of the amplifier. This space is often filled with an electro-magnetic field caused by the mains cables in the area. So we can expect more disturbances. The moving cable will show a movement artifact as well and the influence of the mains will cause a 50 or 60 Hz mains interference in the signal. • Therefore, we have at least three important noise sources when measuring the electro-physiological signal of a muscle.

15. 50 Hz noise in the signal

16. Movement artifact when the electrode is moving with respect to the skin.

17. Artifact when the cable is moving.

18. To get rid of mentioned noise, several measures can be taken. •  1: Movement artifacts that are generated by the movement of the electrode with respect to the skin: • High pass filtering • TMS-I •  2: Mains interference: • TMS-I

19. In many EMG systems, the input amplifier is put on the electrode. This is often called an active electrode

20. Types of EMG • Inserted • Fine-wire (Intra-muscular) • Needle • Surface • Active • passive

21. Fine-wire Electrodes • The most important difference of inserted and surface electrodes is in their band width. • Inserted one has higher frequency • Bw:2_1000Hz(surface electrode’s BW:10_600Hz)

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

23. Surface Electrodes • Active: • with amplifier • Reduce skin impedance( no need to gel) • Reduce motion artifact • Increase s/n • Passive: • Without amplifier • Need to gel & skin preparing • Decrease s/n

24. Surface Electrodes • Advantages • Quick, easy to apply • No medical supervision • Minimal discomfort • Disadvantages • Generally used only for superficial muscles • Cross-talk concerns • No standard electrode placement • May affect movement patterns of subject

25. Factors affecting the surface EMG • It’s a random signal and can’t be represented mathematically. • Many factors affect the observed surface EMG like: • different days even for same person • different people; depending upon individual anatomy, thickness of fat tissue ,cross talk… • Presence of gland & blood vessels. • Characteristic of recording equipment • Position of electrodes.

26. Observed difference from different positions

28. Surface electrodes

29. Needle electrodes

30. Characteristics of EMG Signal • Amplitude range: 0–10 mV (+5 to -5) prior to amplification • Useable energy: Range of 0 - 500 Hz • Dominant energy: 50 – 150 Hz

31. detecting • Raw EMG signal is important • Need filtering or not • It’s difficult to detect signal from noise • Sometimes we need LP,HP or BP filter • Motion artifact, low frequency • Sharp peaks , sudden movement • 60 Hz, ambient noise

32. Data : • Two main parameters that extracted: • Beginning and finishing EMG signal (on & off) (first data) • Increase and decrease of muscle activity. • What can not we conclude? • Strength of muscle • Compare of muscle strength • Voluntary or involuntary motion

33. Abnormal results EMG is used to diagnose two general categories of disease:neuropathies and myopathies Neuropathic disease has the following defining EMG characteristics An increase in duration of the action potential A decrease in the number ofmotor units in the muscle (as found using motor units number estimation techniques) Myopathic disease has these defining EMG characteristics: A decrease in duration of the action potential A reduction in the area to amplitude ratio of the action potential

34. 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

35. Electrode Configuration • Length of electrodes • About 1 cm • Distance between electrodes • Increased amplitude, will increase noise… • 1 cm,2 cm

36. Electrode Placement • Away from motor point Middle of muscle belly is generally accepted • Away from tendon • Away from outer edge of muscle

37. EMG Electrode Placement

38. Surface Electrode Placement

39. Reference Electrode Placement(Ground) • As far away as possible from recording electrodes • Good electrical contact • Larger size • Good adhesive properties

41. Example of the hand and wrist control using the EMG signals: thesubject executed eight hand and wrist motions for about 30 s. The darkened areasindicate no motions because the square sum of EMG (n), which was defined as(1), was below the prespecified threshold. “SUS” in the discrimination resultsindicates the suspended discrimination where E(n) exceeds the prespecifiedthreshold E .

42. The End