The ElectroMyoGraphy (EMG) is the recording of the electrical activity produced when muscles are contracted. Muscle contraction is initiated by motor neurons in the spinal cord. When the motor neuron sends a signal to the muscle to contract, electrical activity is produced by the muscle cells. The EMG records the aggregate activity of many motor cells firing at the same time.
sEMG is measured by placing electrodes on the skin over the belly of the muscle of interest. The raw EMG signal is usually processed further before it can be usefully interpreted. The most common signal adjustments are amplifying and filtering the signal. Because the signal is often very rapid and with transient changes, averaging and smoothing of the signal is often applied.
The frequency range of the raw EMG ranges from 20 up to 500 Hz. When measuring EMG in the vicinity of the heart (e.g. when measuring upper trapezius EMG), be aware of ECG artifacts. The ECG usually interferes between 20-80 Hz. BioTrace+ therefore contains screens that have a range from 100-500 Hz, like the upper trapezius EMG screen. When measuring other muscles, like the frontalis muscle, no ECG correction is required and 20-500 Hz EMG is shown.