![]() ![]() The amplitude of the sEMG signal is in a range from µV to low mV. The resulting EMG signal is bipolar with a symmetrical distribution of positive and negative values, which means that the average value is zero. However, with electromyography you are not able to view and record all MUAPs in a differentiated manner and therefore, the signals are superimposed (Fig. This is because usually, several motor units “fire” and thereby cause the muscle to twitch. However, under normal conditions, it is extremely rare for a single motor unit (which consists of a motor end plate and one or more muscle fibers) to be innervated individually. ![]() If an electrode is now placed above the muscle to be examined, depolarization and subsequent repolarization is measured in the form of a bipolar voltage change. After the original excitation, this zone shifts as a Motor Unit Action Potential (MUAP) at a speed of 2-6 m/s along the muscle fibre. The size of the resulting depolarization zone is described in the literature as approximately 1-3mm². This signal is the so-called action potential (AP), which is conducted from the nerve cells via motor end plates to the muscle. As described above, we use EMG to record the electrical signal that initiates muscle contraction.
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