In an electromyogram, muscle activity is measured and displayed on a diagram, for example. Commercially available EMG devices for home use also use a numerical scale in conjunction with a color background.
The measured muscle activity and the threshold values derived from it provide the basic data for biofeedback therapy. The measurement itself can be carried out in various ways and ultimately depends on the therapy goal: muscle tone can be recorded via electrodes on the skin, anal or vaginal probes or via fine-wire electrodes that are placed under the skin directly in the muscle. Regardless of the electrode placement, the measurement is always based on the same electrical and biochemical processes.2
Electromyography makes use of the electrical properties of the semi-permeable muscle fiber membrane and records the ion balance between the inner and outer space of the muscle cell. In the relaxed, i.e. non-contracted state, the cell interior has a negative charge, while the exterior of the cell has a positive charge. This difference in charge is caused by the different distribution of negatively charged potassium ions and positively charged sodium ions and is referred to as the resting potential, which is usually measured at -80 to -90 mV.3
When the first motor neuron (upper motor neuron) gives a command to the motor nerve to move, transmitter substances are released, which ultimately influence the diffusion properties of the muscle fiber membrane. Positive sodium ions flow into the cell interior, creating a temporary positive charge. This process is known as depolarization. This causes an action potential from -80mV to +30mV. However, the negative charge is restored shortly afterwards by a direct ion return current – repolarization occurs.
The action potential is transmitted as electrical excitation along the muscle fibers, which leads to the release of calcium ions. This triggers chemical processes that cause the contractile cell elements to contract. This results in muscle contraction. The electromyogram measures the action potential of the muscle fibre membrane on the basis of the depolarization-repolarization process and thus depicts muscle activity in a diagram.
Electromyography and the biofeedback therapy based on it are now being used more and more frequently in a diagnostic and therapeutic context. They have also become firmly established in rehabilitation in order to monitor and improve movement patterns and muscle activity during various training sessions. Conveniently designed devices also allow biofeedback therapy to be continued at home.4
Medical research
Ergonomics
Rehabilitation
Sports science
1 https://www.ac-therapie.de/diagnostik-emg-messung/
4 EMG Primer – A practical introduction to kinesiological electromyography, Peter Konrad, Version 1.0 September 2005
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