Selectivity of electromyographic recording techniques: a simulation study.

Abstract

A modified line source model was used to simulate single muscle fibre action potentials and their radial decline as measured using a single fibre (SF), concentric needle (CN) and macroelectromyography (EMG) electrode. The 90 per cent attenuation distance, defined as the distance from the fibre at which the peak-to-peak amplitude of the action potential declines to 10 per cent of its value measured near the fibre, was determined. For the CN and macro electrode this distance was 1·4 and 4·1 times, respectively, the distance measured for the SF electrode Based on the decline characteristics obtained from our simulations and experimental data reported in the literature, we inferred that in a normal human biceps muscle the spike component of CN MUAPs is produced mainly by the action potentials of the closest one-six muscle fibres. This inference was used to interpret the changes in MUAP amplitude seen by clinical EMG in neuromuscular diseases. The decline of action potential amplitude with distance from the electrode was least when recordings were made by the macro-EMG electrode. The three electrodes differed in their uptake area and thus recordings made with them provided complementary information about the motor unit architecture and the way it changes in neuromuscular diseases.