[Methodology and diagnostic potentialities of macro-EMG. I. Methodology]

Macro-EMG records electrical activity from the whole motor unit (MU) as a parameter of its size. The main component of the recording device is a modified single fiber or concentric needle electrode. Different sized uptake areas allow to record with different selectivities from the MU. The teflon insulated shaft surface allows to record with a defined large blank area unselectively macro-signals from the muscle. The conceptual ideas to use a concentric needle in addition to the single fibre electrode is to simplify the trigger-potential recording, which needs to be selective within the MU. In both instances the EMG apparatus has to provide two channels, one for the trigger and the second for an averaging device to record the macro-EMG. The different techniques use the single fiber or concentric EMG-potential as a trigger to average the associated macro-potential from the raw signals. The electrodes different design allow the whole single-fiber-needle to lie within the MU territory whereas the MU is only touched by the concentric needles tip. This implies different recording situations and results. Anatomically macro-EMG size is varied by the recording site of the muscle. The signal is greater close to the endplate zone and declines to stable values about 20 mm apart. For quantitative measurements within a muscle 20 different potentials have to be evaluated for median amplitude, duration and area.