EMG

Electromyography (EMG)

  1. Electro – electrical
  2. Myo – muscle
  3. Graphy – record

Electromyography – involves recording the electrical activity of muscle

Electromyogram – electrical signal associated with the contraction of a muscle

Selected Historical Events Related to EMG

John Basmajian (1921-    1965) wrote the bible of electromyography entitled muscles.De Luca summarized the existing knowledge and research on muscle function as revealed by EMG studies.

ELECTRICAL CHARACTERISTICS

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.

The typical repetition rate of muscle unit firing is about 7-20 Hz.
Damage to motor units can expect at ranges between 450 and 780 mV

Recording of EMG:

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The recording contains the following three phase system.

  • Input
  • Amplifier
  • Display/ Audiovisual Output

Input:

Electrodes

All normal muscles contract, the muscle fiber in the motor unit depolarize and repolarize at the same time and a local disturbance produced in the muscle. This disturbance can detect either by the surface electrodes or needle electrodes (recording electrodes). Two methods can detect this disturbance by monopolar technique or bipolar technique. Three numbers of electrodes used for any study.

1) Recording electrodes

2) Reference electrode

3) Ground electrode

The ground electrode provides a mechanism for canceling out the interference effect of external noise.

Monopolar technique:

In the monopolar technique, the recording electrode should place over the muscle belly or insert in the muscle fibers. The second electrode (reference electrode) placed over the area where the muscle inserted. The reference electrode should a surface electrode. The ground electrode should place near the recording electrode.

Bipolar technique:

In the bipolar technique, the two surface electrodes (recording as well as reference) place over the muscle belly in the longitudinal direction parallel to the muscle fibers and when the needle electrodes used two wires insert through the cannula in the muscle belly. In this method, the ground electrode not needed.

Amplifier:

The electrical activity derived from the body very small i.e. mv or μv and contain undesired signals. The amplifier conditioned to amplify that undesired signals and the useful signals derived from the motor.

Display system:

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After the signal processed and amplified, it displayed on the CRO which permits visual display of the motor unit. The CRO does not provide a permanent record, it only allows the signal to display for a few seconds. However, if a photographic system attached to the CRO a permanent record can obtain. CRO consists of the electric gun, screen, horizontal and vertical plates.

Techniques

Needle electromyography

Skin preparation and Risk

Maximal voluntary contraction

EMG signal decomposition

EMG signal processing

ELECTRODE TYPES

 

  • Intramuscular –

Picture3

  • Needle Electrodes

m,

  • EMG PROCEDURE

Picture2

  • Clean the site of application of the electrode
  • Insert needle/place surface electrodes at muscle belly
  • Record muscle activity at rest;
  • Record muscle activity upon voluntary contraction of the muscle.
  • Needle Electromyography: Techniques
  • A needle electrode is inserted into the muscle
  • The needle is disposable, single use
  • Multiple muscles are accessible for examination
  1. Combination of muscles tested
  • Dependent upon a clinical question
  • Level of discomfort is mild

Needle Electromyography:

Data

  • Insertional Activity
  • Spontaneous Activity
  • Motor Unit Configuration
  • Motor Unit Recruitment
  • Interference Pattern

Needle Electromyography:

Data

  • Motor Unit Configuration
  • Single motor unit:    A motor axon and all its muscle fibers
  • Motor Unit Configuration:    Amplitude, Duration, Morphology
  • Muscle is volitionally activated at different force levels
  • Needle recording properties enable assessment of single MUs
  • Motor Unit Recruitment
  • A pattern of motor unit activation with increasing volitional activation

EMG:  Spontaneous Activity

Fasciculation Potential

Picture1

EMG:  Spontaneous Activity

Positive sharp waves

k

Fibrillation Potentials

l

Skin preparation and Risks

The first step before insertion of the needle electrode is skin preparation. This typically involves simply cleaning the skin with an alcohol pad.

The actual placement of the needle electrode can difficult and depends on a number of factors, such as specific muscle selection and the size of that muscle. Proper needle EMG placement is very important for accurate representation of the muscle of interest, although EMG more effective on superficial muscles as it unable to bypass the action potentials of superficial muscles and detect deeper muscles. Also, the more body fat an individual, the weaker the EMG signal

Maximal voluntary contraction

One basic function of EMG to see how well a muscle can activate. The most common way that can determine to perform a maximum voluntary contraction (MVC) of the muscle that tested.

Muscle force, which measured mechanically, typically correlates highly with measures of EMG activation of muscle. Most commonly this assessed with surface electrodes, but it should recognize that these typically only record from muscle fibers in close approximation to the surface.

EMG signal processing

Rectification knew as the translation of the raw EMG signal to a single polarity frequency (usually positive). The purpose of rectifying a signal is to ensure the raw signal does not average zero, due to the raw EMG signal with positive and negative components. It facilitates the signals and process and calculates the mean, integration and the fast Fourier transform (FFT).

When to order EMG

Mononeuropathy

Mononeuropathy Multiplex

Radiculopathy

Plexopathy (Brachial or Lumbosacral)

Anterior Horn Cell Disorders

Diffuse neuropathies

Cranial neuropathies

Neuromuscular Junction Disorders

Myopathy

When Not to order EMG

Central Nervous System Disorders (Stroke, TIA, Encephalopathy, spinal cord injury)

Multiple Sclerosis

Total body fatigue, fibromyalgia

Joint pain

Unexplained weakness (without a neurologic consultation)

Failed back, S/P multiple necks and low back surgeries

In place of a neurologic consultation

Uses

EMG testing contains a variety of clinical and biomedical applications. It used as a diagnostics tool for identifying neuromuscular diseases, or as a research tool for studying kinesiology, and disorders of motor control.

sometimes EMG signals used to guide botulinum toxin or phenol injections into muscles.

EMG signals also used as a control signal for prosthetic devices such as prosthetic hands, arms, and lower limbs.

Needle EMG may aid with the diagnosis of nerve compression or injury (such as carpal tunnel syndrome, nerve root injury (such as sciatica), and with other problems of the muscles or nerves.

Less common medical conditions include amyotrophic lateral sclerosis, myasthenia gravis, and muscular dystrophy.

EMG then acceleromyograph may use for neuromuscular monitoring in general anesthesia with neuromuscular-blocking drugs, in order to avoid postoperative residual curarization

What to Expect From an
EMG Report

A clinically and physiologically relevant  interpretation/diagnosis

An outline of the localization, severity, and acuity of the process

Notation of other diagnoses that are detected/excluded

Explanation of any technical problems

Utility of EMG

A highly sensitive indicator of early nerve injury

Detects dynamic and functional injury missed by MRI

Provides information regarding chronicity of nerve injury

Provides prognostic data

Highly localizing

Clarifies clinical scenarios when one disorder mimics another

Identifies combined multi-site injury, avoiding missed diagnoses

Identifies more global neuromuscular injury with focal onset

Provides longitudinal data for charting course, response to therapy

Identifies more global neuromuscular injury with focal onset

Provides longitudinal data for charting course, response to therapy

Electromyography and Temperature Feedback techniques

EMG feedback as a muscle re-education technique

In an effort to evaluate the efficacy and function of EMG feedback in muscle reduction, improvement of the abductor function of the abductor hallucis muscle was studied under three training conditions involving

1) EMG feedback,

2) sensory stimulation or

3) equal time for unassisted practice;

4) control condition involving testing without training.

Active range of motion was measured before and after training to assess the ability to use the muscle as an abductor. EMG activity was quantified for a 1-minute test contraction to evaluate the ability to maintain and maximize a voluntary contraction of the target muscle.

The results indicated that EMG feedback was highly effective when subjects had little initial use of the target muscle.

EMG feedback improved the ability of these subjects to maintain and maximize voluntary muscle contractions, as demonstrated on the EMG measure.

EMG feedback did not add to the learning situation when only a relatively brief, phasic contraction was required, as on the range-of-motion measure; similar gains were made with equivalent practice without EMG feedback.

When subjects already had considerable use of the target muscle prior to training, EMG feedback may have actually interfered with training; in this case, an unassisted practice was more effective.

Skin Temperature Biofeedback

Skin temperature biofeedback, also called Thermal Biofeedback, the most common of all biofeedback techniques. Temperature biofeedback focuses on teaching you to alter your hand temperature.

A thermistor attached to one finger of your dominant hand. Changes in temperature as small as one-tenth of a degree are registered and fed back to you through a digital display. Your job to increase or decrease the temperature of your hand.

Using thermal biofeedback relaxation to alter the temperature of the body one of the first biofeedback techniques to use for healing.

Researchers found that this particular method useful in treating Raynaud’s phenomena and migraine headaches.
EMG Muscle Tension Biofeedback.

EMG biofeedback technique gives feedback about what happened in a particular group of muscles, for example in the forehead or forearm. This feedback usually both visual (digital display) and auditory (clicking sounds). With this feedback, you can learn to voluntarily relax or tense particular muscle groups.

When muscles tighten, a series of electrical impulses travel to the muscle fibers. With the decrease of electrical activity, relaxation of the muscles occurs. With EMG biofeedback, the electrical activity of the muscle detected the used of electrodes placed on the skin directly over the muscle that measured. The information is then fed back to you.

Your goal to decrease (or increase) this electrical activity, thus learning to control your muscle tension.

EMG biofeedback found to be particularly useful for tension headaches, anxiety, phobias, and insomnia.

Electroencephalogram (EEG) Biofeedback

EEG biofeedback, also called neurofeedback, a learning strategy that allows you to alter your brain waves. As you watch your brainwave pattern on a monitor, you learn that you can change your brainwaves.

Why would you want to change your brainwaves? Simple. 4 brainwave patterns (beta, alpha, theta, and delta), each associated with a different state. If you look for stress relief, then your goal to learn to induce alpha brainwave patterns, associated with relaxation and calmness.

In a typical EEG session, one or more electrodes placed on your scalp, and one on each ear. Your brainwaves monitored and displayed on a monitor. Through a computer game, you learn how to change your brainwaves to a more desired frequency.

EEG biofeedback used for anxiety, depression, insomnia, chronic pain, addictions, chronic fatigue syndrome, and autoimmune disorders.