MOTOR UNIT ACTION-POTENTIALS RECORDED WITH CONCENTRIC ELECTRODES - PHYSIOLOGICAL IMPLICATIONS

Computer simulations of concentric needle electrode recording characte ristics assume a hemisphere spatial recording territory for the electr ode's core with the cannula shielding electrical activity arising from those muscle fibers located behind the cannula with respect to the el ectrode's core. It is also believed that the motor unit action potenti al's (MUAP) duration is generated by the number of muscle fibers withi n the electrode's hemispherical recording territory. This presumption suggests that rotating the needle will necessarily alter the number of muscle fibers within the hemispherical recording territory and hence lead to an alteration in MUAP duration. Comparisons were performed for different needle orientations with documentation of no statistically significant alteration in MUAP duration. Additionally, referential rec ording montages with the concentric needle electrode revealed that the electrode's core records MUAPs with durations comparable to those det ected by the cannula. These findings strongly suggest that the recordi ng territory of the concentric needle electrode, with respect to MUAP duration, is not a hemisphere but a sphere encompassing most if not al l of the MUAP's muscle fibers in a manner similar to that of a monopol ar needle. These findings have significant implications regarding pres ently used MUAP simulation techniques and require a reconceptualizatio n of how the concentric needle electrode records electrical activity w ithin a volume conductor. (C) 1997 Elsevier Science Ireland Ltd.