Detecting single muscle fiber activity using a concentric needle electrode: a simulation study

Based on the line source model, simulated concentric-needle-detected motor unit action potentials (MUAPs) were transformed into compound weight functions using inverse-average-current filtering. The numbers of significant individual muscle fiber contributions to the compound weight functions were estimated using acceleration thresholds. The ability of the technique to detect the contribution of single fibers to a MUAP was evaluated. For fibers that contributed muscle fiber action potentials (MFAPs) with maximum slopes larger than 2.4 V/s to a MUAP, the correlation between the expected number of contributing fibers and the number measured was 0.95 and no significant bias existed. The spatial distribution of fibers that could be detected was found to be approximately semicircular with a radius of 300 μm. This capacity to detect the activity of single fibers will allow the concentric needle electrode to be used in ways comparable to that of the single fiber electrode