Theory of electromyography

Theory of Electromyography

Electromyography is a willpower that handles the detection, examination and use of electronic signal that emanates from skeletal muscles. The electromyography is researched for various reasons in the medical field. A good superficial acquaintance with medical literature will find out various current applications in domains such as neuro physiology, kinesiology, engine control, psychology, rehabilitation, remedies and biomedical anatomist.

The EMG signal is the electronic manifestation of the neuromuscular activation associated with the contracting muscles. The signal represents the existing produced by the ionic flow over the membrane of the muscle fibers which propagates through the intervening tissues to attain the diagnosis surface of the electrode positioned in the environment.

It is an exceedingly complicated sign which is influenced by anatomical and physiological properties of muscles and the control system of the nervous system, as well as characteristics of the instrumentation used to detect and see it.

Most of the romantic relationships between your EMG signal and the properties of contracting muscles that are used have advanced serendipitously. Having less proper description of the EMG sign is just about the greatest solo factor that has hampered the development of electromyography directly into a precise self-discipline.


  • To test the nerve and muscle activity
  • To determine nerve conduction velocity to check nerve damage/compression
  • To obtain firing characteristics of nerves.
  • Analysis of motor product action potentials
  • To analyze the scope of nerve destruction, muscular damage
  • It pays to for health club trainees and sport people to evaluate development and development of specific muscles.
  • It is useful for energy/tiredness analysis of commercial workers for time-motion-rest routine evaluation for an efficient working environment.
  • Usually passenger pilots are checked because of their EMG levels before they take up a airfare to be able to ensure fatigue degree of the pilot is at safe level.


About 40% of the body is skeletal muscles and another 10% is easy muscles of internal organs and cardiac muscles from the heart. Here our company is interested in characterizing the function of skeletal muscles. The principal function of skeletal muscles is to generate force. Because of this, these are excitable. Thus skeletal muscles have 2 fundamental properties. They can be excitable(in a position to respond to stimulus) and contractible(in a position to produce pressure). A skeletal muscle contains numerous fibers with diameters which range from 10 to 80 m. Each muscle fibers includes hundreds to thousands of myofibrils. Each myofibril has about 1500 myosin filaments and 3000 actins filaments lying down side by side.

Cell Potential:

The nervous system is made up of neuron skin cells. Neurons are the conducting components of the nervous system and are responsible for transferring information across the body. Only these and muscle skin cells are able to generate potentials and they are called excitable skin cells. Neurons contain special ion stations that allow the cell to improve its membrane potential in response to the stimuli the cell receives.

Receiving Potential:

All cells in the body have a cell membrane surrounding them. Across this membrane there can be an electric charge known as the resting probable. This electric impulse is produced by differential ion permeability of the membrane. In the skin cells, potassium (k+) stations allow diffusion of k+ ions from the cell while Sodium(Na+) ions diffuse into the cell. This Na+-K+ pump, which requires ATP to use, pumps two K+ ions in to the interior of the cell for each and every 3 Na+ ions pumped out. K+ and Na+ ions are continually diffusing across the membrane from where they were just pumped, but at a slower rate. Since there are definitely more K+ ions inside the cell than outside the house, a potential exists.

Action Potential:

Some skin cells, such as pores and skin cells aren't excitable. Other cells such as nerve and muscle cells are excitable. When a simulating electric field acts on an excitable cell, the Na+ permeability rises, Na+ gets into the cell interior and the entering positive fee depolarizes(reduces to approximately zero), the transmembrane probable. Later the K+ permeability raises and K+ ions stream out to counter this result. The Na+ gates close followed by the K+ gates. Finally, the resting probable is regenerated. The action potential lasts about 1ms in nerves and about 100 ms in cardiac muscle. It propagates in nerves at about 60 m/s and bears sensations from the periphery toward the mind via sensory nerves. Through motor nerves, the brain commands muscles to contract. We can analyze the action potential propagation velocity v=d/t where

Figure shown here symbolizes the role of voltage-gated ion channels in the action probable. The circled quantities on the action potential match the 4 diagrams of voltage-gated sodium and potassium channels in a neuron's plasma membrane.

Motor Device:

The most fundamental unit of your muscle is called the Motor Unit. It consists of an alpha-motoneuron and everything the muscle fibers that are enervated by the motoneuron's branches. The electrical signal that emanates from the activation of muscle materials of a motor product that are in the detectable vicinity of an electrode is called MOTOR UNIT ACTION POTENTIAL (MUAP). This constitutes the essential unit of the EMG transmission.

A Schematic representation of the genesis of any MUAP is shown above. There are numerous factors that effect the form of MUAP. Some of these are

The relative geometrical relationship of the diagnosis surface of the electrode and the muscle fiber of the motor device in its vicinity. The relative position of the diagnosis floors to the innervated area, which is the region where in fact the nerve branches contact the muscle materials. The size of muscle fibres, because amplitude of specific action potential is proportional to the diameter of the fibers, and The amount of muscle fibers of an individual motor device in the detectable vicinity of the electrode.

The last two factors have particular importance in professional medical applications. Sizeable work has been performed to identify morphological changes in the MUAP shape resulting from changes in the morphology of the muscle materials or the electric motor unit such as regeneration of motoneurons. Although utilization of MUAP condition evaluation is common practice among neurologists, interpretation of the effect is not necessarily self-explanatory and relies greatly on the knowledge and disposition of the observer.

To support muscle contraction, the engine product must be triggered repeatedly. The causing collection of MUAP's is called Motor Device Action Potential Train(MUAPT). So, EMG transmission can be synthesized by linearly summing the MUAPT's as they can be found when they are diagnosed by the electrode where mathematically generated MUAPT's are added to yield the indication in the bottom.


As an action potential vacations along a electric motor nerve to muscle fibers, it initiates an action potential along the muscle fibre membrane, which depolarizes the muscle fiber membrane and travels with in the muscle fiber. The Subsequent electro-chemical reaction with in the muscle fiber content then initiates attractive causes between the actin and myosin filaments and causes them to slip together. This mechanism produces muscle contraction.

Tension is developed in the muscle as it contracts. You will discover 3 types of contraction

  • Isometric
  • Concentric
  • Eccentric

Isometric or Static Contraction means a muscle agreements without change in its duration. Concentric Contraction occurs whenever a load is significantly less than the isometric power made by the muscle and the strain shortens the muscle. Eccentric Contraction occurs when the load is higher than the isometric pressure and elongates the contracting muscle.

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