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The development of this technique began with Francesco Redi’s documentation in the year 1666. Then an Italian physician Luigi Galvani discovered that the contraction and force of the muscular tissue causes stimulation. The further progress took place when Herbert Gasser and Joseph Erlanger attempted to record nerve impulses and improve the cathode ray in 1922. However, the first modern EMG machine was created by Herbert Jasper years later in 1942.
Applications of EMG
- It helps in Kinesiology that aims to determine the degree and sequence of contraction of various muscles participating in a movement use.
- It is used in the mechanism employed by the body for grading the force of muscular contraction.
- Helps in the process of clinical diagnosis and follow up of myopathies and responses of nerve and muscle to injury.
- EMG is frequently used in various kinds of research laboratories like neuromuscular physiology, biomechanics, movement disorders, motor control and many more.
Equipment required in the process
- Electrodes
- Surface electrode – placed on the surface of the skin
- Needle electrode – pierced through the human skin and this electrode lies inside the muscle that is to be tested.
- High gain amplifier (with the frequency range of 10-5000Hz)
It amplifies the electrical signal that has been taken up by the electrodes and passes it to the oscilloscope to which it is connected. The oscilloscopic traces might be photographed, stored on a magnetic tape or even a hard disk nowadays. The EMG Signals are then fed to an audio unit to have the on-the-spot feel and the analysis for the amplitude and frequency of the action potential generated by the muscles.
- An arrangement to record the output
It requires:
- A specially made shielded room to conduct the EMG test in the best possible manner.
- A monitor to see the electrical activity of the skeletal muscles
Motor Unit
The motor neuron and motor fibers supplied by it.
MUP
The sum total of the action potentials produced by the unit in the muscle fibers stimulated by single motor neuron. It is characterized by the number of phases, its duration, rate of rise and amplitude of the first component.
Factors that affect Motor Unit Potential
Physiological factors
- The age of the patient
- The size of the muscle examined
- Body temperature of the person
- Room temperature where the recording takes place
Technical factors
- The type of electrode used (needle electrode tends to produce more accurate findings over the surface electrode)
- The characteristics of the recording surface (that is if the skin is hairy, sweaty or oily then it will affect the MUP accordingly)
- Electrical properties of the cable
- Preamplifier and amplifier
- The method of recording
Process of EMG Analysis
The following are the two ways in which the EMG analysis can be done:
- Qualitative Analysis
It involves a visual review of the record to find out if there is any abnormality in the muscle on the nerve.
- Quantitative Analysis
It begins with analysis of the data of amplitude, duration and frequency that is obtained and is followed by Power Spectrum Review/analysis in which the patient is asked to do the muscle contractions at various degrees in order to find out the force of contraction that is reported on the EMG monitor.
Different patterns of EMG and findings in each case
Pattern of EMG | Recording | Findings |
Resting activity | Relaxed muscle and needle not moving | No sort of electrical activity is recorded though there may be slight fluctuations due to the miniature potential |
Insertion activity (Only seen when needle electrodes are used and not visible with surface electrodes) | The needle is pierced through the skin of the patient to several sampling spots within the insertion tract. | Some brief action potentials are recorded |
Motor unit potential (Potential of the sum of the skeletal muscle activations which are done by single motor unit) | The needle is not moved while the patient is instructed to make slight muscle contraction | A few motor unit action potentials are activated and those may be biphasic or triphasic but it is usually of short duration. |
Recruitment | The patient is asked to make progressively stronger muscle contraction until maximum force is reached | The number of functioning movements until the baseline is obscured increases as there is recruitment of motor units with each increasing the force of contraction. |
Conclusion
The advancement of EMG began in 1666 with Francesco Redi’s documentation. Then an Italian doctor named Luigi Galvani found that muscular tissue contraction and force cause stimulation. Some applications are: It aids in Kinesiology, which aims to understand the extent and sequence of compression of various muscles involved in movement use, It is used in the body’s mechanism for evaluating the power of muscular contraction.
