Possible inaccuracies in determining the excitation spreading velocity in surface-led potentials of single human motor units.

The proposed work examines the possible inaccuracies in determining the propagation velocity of the excitation along the muscle fibres, resulting from the incorrect positions of the leading off electrodes. The recording of the single motor units (MUs) was performed using a multielectrode consisting of two monopolar electrodes with small leading-off areas at an interpole distance of 10 mm from one another. The selectively recorded activity of MU using a wire branching electrode (Gydikov et al., 1986), placed proximally to the surface multielectrode, served as a trigger in the averaging of the potentials of the single MUs. The velocity was determined by the time measured between the negative peaks of the potentials recorded with the surface electrodes. The results have shown that the values of the measured propagation velocity of the excitation along the muscle fibres outside the so-called "correct position" for velocity determination (far from the motor endplate and far from the end of the muscle fibres--Gydikov, Gantchev, 1989) increase to 20%. The velocity measured near the motor endplate area increases by an average of 13.85 +/- 6.38% to the end of the muscle fibres--by an average of 12.99 +/- 6.23%. The data obtained are particularly relevant to clinical practice using methods involving the surface-recorded potentials for determining the propagation velocity of the excitation along the muscle fibres.