What Is an Electromyograph?

Electromyogram (EMG) refers to the bioelectrical pattern of muscles recorded with an electromyograph. It is of great significance to evaluate human activities in human-machine systems. Can be measured with a dedicated electromyograph or a polysomnography. The graph measured during static muscle work shows three typical waveforms of simple phase, mixed phase, and interference phase, which are very closely related to muscle load intensity. When the muscle is lightly loaded, there is a single low-amplitude motor unit potential isolated on the map with a certain interval and frequency, that is, the simple phase; when the muscle is moderately loaded, a single motor unit potential is still visible in some areas on the map However, the potentials in other areas are very dense and cannot be distinguished, that is, mixed phases; when the muscle is heavily loaded, high-frequency potentials with different frequencies, different amplitudes, and uneven overlaps are difficult to distinguish, that is, interference phases. The quantitative analysis of this figure is more complicated and must be completed with the help of a computer. Commonly used indicators include integral electromyogram, mean square amplitude, amplitude spectrum, power spectral density function, and average power frequency and center frequency derived from the power spectral density function. ^[1]

Muscle fibers (cells), like nerve cells, have high excitability and are excitable cells. The first reaction that occurs when they are excited is the action potential, that is, the conductive potential that appears on both sides of the cell membrane where the excitement occurs. The contractile activity of the muscle is further caused by the action potential of the cell excitement transmitted along the cell membrane to the deep part of the cell (through the excitement-contraction mechanism).

When the muscle fibers are quiet, there is only resting potential, that is, the potential difference between the inner and outer sides of the cell membrane when it is not stimulated, also known as the transmembrane resting potential, or membrane potential. The resting potential was negative inside and outside the membrane. Conventionally, the potential outside the membrane is zero, and the potential inside the membrane is about -90mV.

When the muscle or nerve cell is stimulated, it generates excitement. The resting membrane potential at the excited site changes rapidly. First, the membrane potential decreases. When it reaches a certain critical level, it suddenly changes from negative to positive membrane potential. The rapid change returns to the negative potential and returns to the normal negative resting membrane potential level. A short, rapid, and reversible change in membrane potential during such excitement forms an action potential. It is always accompanied by the generation and spread of excitement, is a characteristic manifestation of cell excitatory activity, and is also a sign of nerve impulses.

Under normal circumstances, muscle fibers are always excited and contracted under the control of the nervous system. This process is caused by motor neurons that innervate muscle fibers, emit nerve impulses (action potentials) and conduct them to the periphery along the axons, release acetylcholine as a transmitter, and realize the excitation transmission at the motor-muscle junction. In short, the bioelectrical phenomenon of muscle fibers and motor neurons during excitement is just the manifestation of their functional activities.

EMG measurement is based on the above bioelectrical phenomena. Extracellular recording electrodes are used to guide the compound action potential of muscle excitatory activity in the body to the electromyograph. After proper filtering and amplification, the amplitude, frequency and waveform of potential changes can be measured. Display on the recorder or on the oscilloscope.

Electromyographs usually consist of amplifiers, oscilloscopes, recorders, monitors, stimulators, and averagers. The averager is an indispensable part of modern EMG machines, and its main function is to extract the required electrical signals from noise. In addition, the electromyograph also has a variety of accessories, such as various electrodes, oscilloscope cameras, etc. Some are also equipped with special computers and electronic memory systems. Using computer technology, it can be used for automatic analysis of EMG.

There are two types of electrodes that can be used in EMG measurement: one is the skin surface electrode, which is placed on the skin surface to record the electrical activity of a whole muscle, so as to record nerve conduction speed, spinal cord reflection, and muscle involuntary Movement and so on; the second is the coaxial single-core or double-core needle electrode, which is inserted into the abdomen of the muscle to detect the motor unit potential. Needle electrodes are commonly used in medicine, and insertion into the muscle under test can cause pain, so it should not be abused when measuring the texture of food. Under the same conditions, the potential recorded using the smaller electrode area is greater than the larger one. Therefore, in food texture analysis, skin surface electrodes are often used. Its advantage is that it does not cause pain, and it is often used to record the induced EMG response when measuring nerve conduction velocity. The surface electrode is usually composed of two small discs (about 8mm in diameter) or rectangular (12mm × 6mm) stainless steel, tin or silver plate. It is placed on the surface of the skin covered by the EMG muscle. It depends. According to reports, when measuring the EMG of masticatory muscles with surface electrodes, if the distance between the two poles is 3.5 to 40mm, the average EMG voltage increases with the distance between the poles; if the distance between the poles reaches 50ram, the average voltage no longer increases, but instead Downward trend. In the measurement of masticatory muscle EMG, the general distance between the poles can be 15-20 ram. The electrode should be in good contact with the clean skin surface. The skin surface can be coated with conductive paste or physiological saline, and the skin resistance should be less than 10k12. Interference can occur when poor contact or too much skin resistance. Surface electrodes cannot be used to guide the electrical activity of deep muscles. Even superficial small muscles cannot be used to guide the single motor unit potential and high-frequency components of EMG.

There are usually two types of EMG analysis methods, namely quantitative analysis and simulation analysis. Quantitative analysis needs to measure EMG waveforms and amplitudes to obtain certain parameters that represent the characteristics of myoelectric activity, such as average voltage, number of discharges, time of discharge period, chewing period, rest period time, etc. EMG parameters were compared between the participants. The advantage of this analysis method is that it is more accurate, but the measurement and calculation process is more complicated. Simulation analysis is to directly observe and compare EMG between different subjects or different foods, and find some changes in EMG properties, which can be empirically inferred. This method is relatively simple and easy to implement, but it needs to be tested repeatedly for verification.

This test can be used in medicine to determine the functional status of peripheral nerves, neurons, neuromuscular junctions, and the muscles themselves.

Electromyography

By measuring the time limit and amplitude of the motor unit potential, the presence or absence of spontaneous electrical activity in quiet conditions, and the wave shape and amplitude of muscle contraction, it is possible to distinguish between neurogenic and myogenic damage, and diagnose acute and chronic spinal anterior horn damage (Such as pre-poliomyelitis, motor neuron disease), nerve root and peripheral neuropathy (such as EMG can help determine the location, extent, extent and prognosis of nerve damage). In addition, it has diagnostic value for nerve entrapment lesions, neuritis, genetic metabolic disorder neuropathy, and various muscle diseases. In addition, EMG is also used to track the recovery process and efficacy of diseases during the treatment of various diseases.

In food texture testing, the use of normal skin surface electrodes has the advantage of not causing pain, and is often used to record the induced EMG response when measuring nerve conduction velocity. The main masses are the masseter muscle and the temporal muscle. The two main muscles that control chewing are because they are located just below the cheeks. The measurement is convenient, so there are many related studies. ^[3]

Sakamoto et al. (1989) studied the chewing patterns of 43 foods using electromyography. It was found that when the mouth is closed, the chewing energy of the masseter muscle can vary from 3 to 108, and when the mouth is opened, the chewing energy of the chin muscle can change from 13 to 154. between.

In 1994, Brown measured the electromyogram of adults when they ate chewing gum. It was found that for individuals, the electromyogram was very reproducible and had a certain time stability, but the electromyogram of different people was significantly different. However, in the study, the subjects stated that the electrodes attached to the face did not interfere with normal chewing activities. Brown confirmed that the chewing pattern is relatively stable for each individual and each food. They used electromyography to measure the rate of chewing, the persistence of chewing, the work of chewing, the formation of bolus, and the process of swallowing.

In 1998, KohyaITIa et al. Used electromyography to study the texture of rice and found that rice with high amylose content requires high electrical activity in the masseter muscle. The difference between different varieties of rice at the first bite is quite large. Later, K.hyama et al. Reported that the correlation between the number of chewing times, chewing time, and chewing duration (determined by electromyography) and adhesiveness was higher than the correlation with hardness. They also found that the difference in chewing patterns between testers was greater than that among different rice varieties.

Kohyama et al. (2007) used EMG to study the chewing behavior of people on lumps and shredded foods (different sizes). A plastic spoon is provided to a common subject in a random order with a mouthful of raw carrots, cucumbers, roasted meat, or fish balls (7-gram pieces, equally-weighted samples, equally-sized samples). Subjects can gargle with water before or between trials without telling them which sample they are tasting, and raising their hands after each swallowing of the sample. The results show that masseter muscle activity is closely related to chewing force. Surface EMG shows harder foods. The greater the chewing force, the greater the masseter muscle activity, the longer the chewing time, and the more chewing times. When chewing flexible food, people chew more slowly. The chewing speed can also be determined by the working time of the EMG's chewing muscles and the time of one chewing cycle. To obtain a certain amount of nutrition, the finely chopped foods do not require effort due to the increase in volume. Equal amounts of finely cut foods show increased or at least similar ease of chewing, but equal volume of finely cut foods show less chewing activity. Regardless of the hardness and toughness of the food, finely cut food may be more difficult to consume.