Frequency and time domain characteristics of single muscle fibre action potentials

Action potentials of single muscle fibers (brachial biceps) were recorded with a multi-electrode, ensuring a minimum fibre-electrode recording distance. Propagation velocity was measured in 15 fibres and the power spectral density of the action potentials was computed through a FFT algorithm. Linear correlation was found between action potential amplitude (peak to peak) and propagation velocity, as well as between maximum-minimum amplitude time (defined as the time interval between the positive and negative peaks) and propagation velocity. Assuming al linear dependence between propagation velocity and muscle fibre diameter, a linear relation between the fibre thickness and the extra-cellular action potential was derived from the action potential amplitude/propagation velocity curve. The action potential power spectrum had a band pass form, with peak magnitude of 1.61+/-0.03 kc/sec, and -3 dB points at 0.98+/-0.19 kc/sec and at 2.41+/-0.53 kc/sec. A linear relation was found between the spectral peak magnitude and propagation velocity, and between the ban width and the propagation velocity, as predicted by a mathematical model describing the power spectrum of single fibre action potentials.