Myokymia is characterized electrophysiologically by rhythmic or semi-rhythmic bursts of a single motor unit discharging several times a second at a rate of 3-8 Hz. These myokymic discharges are nonsynchronous in different muscles or even in the same muscle, with intervals of 100-200 milliseconds separating individual bursts. The spontaneous discharges are not initiated by voluntary movement, although they may increase with such activity.