title: The calculated radial decline of the extracellular action potential compared with in situ measurements in the human brachial biceps.
abstract: Action potentials from 16 single muscle fibres were recorded with a multi-electrode from the human brachial biceps. Propagation velocity was calculated for 10 of the fibres, and the volume conduction at distances of 79, 152 and 251 micrometer, was measured for 6 of these fibres. The radial decline of the action potentials was calculated from the Fourier transform of the action potential at the origin, simulating the low-pass filter characteristics of the muscle tissue by sections of RC elements. A good agreement was found between the calculated data and the experimental data on the radial decline of the action potentials. The 90% attenuation radius of the action potential recorded with a 25 micrometer electrode, calculated for 16 action potentials, was derived from the volume conduction calculations. The average value found was 191 +/- 20 micrometer. A linear correlation was found between this radius and the peak spectral amplitude of the action potentials. Likewise, a linear correlation between the 90% attenuation radius and the propagation velocity of the fibres was confirmed.
mesh_terms: D000200:Action Potentials; D000328:Adult; D004576:Electromyography; D005583:Fourier Analysis; D006801:Humans; D008954:Models, Biological; D009132:Muscles / Q000502:physiology*