Quantitative electromyography: a new analogue technique for detecting changes in action potential duration.

An automatic method using an analogue analyser is described for obtaining an index which is based on the mean phase duration of an EMG signal. This method gives similar values for motor unit action potential duration to an alternative digital method of analysis based on the distribution of time intervals between zero crossings of the EMG signal. The analysis has been found to give good discrimination of normal and myopathic EMG signals.