Effect of parameters altering with muscle fibre functional state on power spectra of spatially filtered extracellular potentials.

We aimed to analyse the effect of parameters altered with muscle fibre functional state on power spectra (PS) and spectral characteristics of the signals detected from skeletal muscle fibres of finite length by bipolar or one-dimensional multi-electrodes oriented in parallel to the muscle fibres. The PS were calculated as the product of the power spectrum of the input signal (the first temporal derivative of the intracellular action potential (IAP)) and spatially filtered impulse response. A multi-electrode with an even number of poles, located above the end-plate or fibre end, reduces the effect of alterations in the propagation velocity and increases that of the IAP duration and after-potentials. Detection of the signals far from the end-plate and fibre ends reduces the effect of the IAP spike duration and increases that of the propagation velocity. Increasing the number of poles reduces the effect of after-potentials. A proper multi-electrode arrangement and position could help to separate and assess the relative alteration of individual parameters.