Anatomically accurate model of EMG during index finger flexion and abduction derived from diffusion tensor imaging
Fig 6
Influence of physiological and anatomical factors on the EMG amplitude.
(a) MUAP peak-to-peak amplitude (maximum across four bipolar channels) as a function of distance from the electrode. The number of fibers in each motor unit is indicated by the diameter of the discs and the muscle state is indicated by their color: green for index finger abduction and blue for flexion. The electrical profile of the muscle over the cross-section directly under the electrode array is shown in (b) and (c) for abduction and flexion, respectively. This profile illustrates the normalized electric potential detected at the EMG array (averaged over the five electrodes) by virtual point current sources distributed over the muscle cross-section. The reference voltage Vmax corresponds to the maximum voltage produced by these point sources across the two muscle states. Dashed lines mark levels of 5% decay in the voltage produced at the array. Center points and territories of simulated motor units are also shown. MUs for which the amplitude of their surface action potentials lay below the noise level are indicated by dotted black lines. Amplitudes of the surface action potentials for the remaining motor units are indicated by the color of the center point and the territory line, according to the color scale on the left side of the figure—same scale used in (a).