A Study of Synchronous Activity of Paretic Muscles in Human Poliomyelitis by Means of Vector Electromyogram

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Abstract
Coaxial double electrodes and multielectrodes 0.1, 1, 2, and 3 mm apart were inserted perpendicular to the muscle fiber, and double leading was performed from 2 points within one motor unit. Each action potential was added to the X and Y axis deflecting plates of cathode ray tube, and Lissajous figure was obtained from which correlations of the 2 lead points were computed, during voluntary contraction. The action potentials from one motor unit were sometimes temporally displaced when the distance between the lead points was as small as 0.1 mm. The displacement of the discharge time always occurred when the distance between the lead points was 1 mm. This time displacement computed from the Lissajous figure was expressed in terms of phase angle. The mean phase angle of the paretic muscles examined was about one half of that of normal muscles. This small mean phase angle indicates that the activities of muscle fibers belonging to one motor unit are close to absolute synchronism in paretic muscles, and further that the vector summation of action potentials of individual muscle fibers can be larger than that in normal muscles. Concerning the genesis of the temporal difference in action potentials from two points which supposedly belong to one motor unit, the spatial dispersion of the nerve endings, and differential conduction velocity among muscle fibers were considered; since the spatial dispersion and the difference in conduction velocity were smaller in paretic than in normal muscles, these factors were considered to be the major source of the temporal difference in action potentials. Using double leading from 2 points along one motor unit, the conduction velocity of muscle fibers was measured on paretic muscles. The conduction velocity ranged from 5.0 to 8.3 m/s with the mean of 6.8 m/s. The previous finding that the amplitude of action potential is higher in paretic muscles than in normals was confirmed, and was explained by closeness of synchronous activity of muscle fibers belonging to one motor unit to the absolute synchronization.

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