The procedure by which a measurement obtained from a particular muscle and subject is expressed as a percentage or proportion of a reference measurement obtained from the same muscle and subject. For example, the amplitude of an EMG signal might be expressed as a fraction of the EMG signal amplitude recorded during an MVC of the same subject.Normalization of the EMG amplitude to a reference value enables comparisons between subjects/muscles/measurement sessions/ electrode positions, etc. To interpret and compare the RMS or ARV amplitude of EMG signals they must be normalized, as a number of factors that are unrelated to muscle activity can influence the recorded voltage (e.g., thickness of subcutaneous layers).