Motor unit analysis. Comparison between concentric and monopolar electrodes

Motor unit action potential (MUAP) measurement parameters are reported to be affected by the type of needle electrode. MUAP amplitude measured with monopolar electrodes has been reported to be up to twice the amplitude recorded with concentric electrodes. We hypothesized that with current technology the difference in recordings from the two needles should be minimal and of little clinical significance. The right extensor digitorum communis muscle was examined in 15 healthy volunteers with first a concentric and then a monopolar needle. The filter band-pass of the electromyograph was 20 Hz to 10 kHz. Four first-recruited MUAPs were isolated by using each electrode. A separate muscle insertion was performed to locate each potential. Amplitudes were maximized. Consecutive MUAPs were averaged and measured. The mean (+/- SD) values of the measurements were as follows: amplitude: monopolar, 1038 (+/- 369) microV; concentric, 912 (+/- 315) microV; duration: monopolar, 10.8 (+/- 2.0) ms; concentric, 9.7 (+/- 1.7) ms. No statistically or clinically significant differences exist between these measurement values.