[Number of spike-components contributing to the motor unit potential (author's transl)]

40 motor unit potentials recorded with concentric needle electrodes (Fig. 1) from the extensor digitorum communis muscle were analysed in order to find out the number of contributing muscle fibre action potentials. A "fractionation" of the motor unit potential was achieved by maintained voluntary activity under ischemic condition leading to a consecutive transmission block in the motor endplates within the active motor unit. Thus one after the other muscle fibre action potential failed to occur leading to a stepwise reduction of the motor unit potential which finally was abolished (Fig. 2 and 3). With technique it was shown that 65% of the area of the investigated motor unit potentials were composed of two to twelve (mean 5) muscle fibre action potentials (Fig 4). No correlation between the number of spike-components and duration or amplitude of the motor unit potential was found (Fig. 5). The non-analysed area of the motor unit potential probably represented activity of more distant muscle fibres of the motor unit.