According to BUCHTHAL the histogram of duration and voltage from the motor unit of biceps brachii muscles gives only one peak respectively as can be seen in Fig. 14 in his paper which reports the data covering the experiment on 1,268 motor units. However, his histogram seems to be made of the spikes led off from several motor units because the histogram shows no much fluctuations in voltage as 50μV to 1,000μV and in duration as 1
msec to 20 msec. Therefore, if observations are actually based on a single motor unit, two peaks may reasonably be expected on the histogram, because two kinds of the motor units, kinetic (phasic) and tonic, have respective individual characteristics of their own shikes The histological observation shows that many white and red muscle fibers are intermingled with each other even in one single fasciculus, and it is supposed that the fasciculus does not correspond to a single motor unit. Moreover, the shape of the spikes, which was formerly considered as a motor unit, is not a pure diphasic form, but irregular and polyphasic ones, and also electromyographically a single motor unit controls the area of more than 10mm in width (BUCHTHAL). From these facts, it is probable that the histogram by BUCHTHAL was made of the spikes composed of muscle fibers belonging to several different motor units.
Our observations done by the above stated method showed clearly the pure diphasic spikes. Therefore, we are of the opinion that these spikes obtained by our method are led off from only one or from a few muscle fibers belonging to the same motor unit. These spikes are lower than 550μV
in voltage and shorter than 5.5 msec in duration and every individual spikes show uniform diphasic pattern. There exist two kinds of spike groups, in the histogram one which is composed of high voltage with short duration (1.0-1.5 msec.), and the other of low voltage with long duration
(2.0-4.0msec.). The former may be of kinetic (phasic) motor unit and the latter is of tonic motor unit, because the white muscle fibers with a larger diameter may have a higher voltage than the red and the white fibers that perform rapid contraction may show shorter duration in wave form. In the two cases having spinal cord tumors, two kinds of spikes with respective and individual characteristics were observed in the same EMG. These will be two different kinds, kinetic (phasic) and tonic motor units. In the case of amyotrophic lateral sclerosis, two kinds of spikes appeared, but since both of them were of short duration, they might be considered to be of kinetic (phasic) motor unit (or its intermediate motor unit). Furthermore, since its histological findings revealed that the red muscle fibers were all atrophied and degenerated and showd only white muscle fibers to be normal, it is obvious that the kinetic (phasic) motor unit with a shorter
duration is derived from white muscle fibers. Therefore, in our opinion the widely accepted concept that spikes including even irregular wave forms all belong to the motor unit seems not to be true, but these spikes seem to represent a combination of several pure spikes though not so many, and those muscle fibers belonging to the same motor unit appear to be intermingling themselves in a relatively wide area. The reason for this contention may be explained as follows. If the muscle fibers belonging to the same motor unit were agglomerated, clearcut diphasic
spikes should appear even with a fairly big electrode, and if the accepted concept be true, these spikes can never be picked up at the distance so far apart as 2.0cm. or 2.5cm. (0.5-1.2cm. by BUCHTHAL) as has been possible in our experiments. Furthermore, the histogram composed only of these pure spikes reveals two peaks, and therefore, we believe it is reasonable to say that these two peaks indicate the existence of kinetic (phasic) and tonic motor units. As a small number of motor units located in between these two peaks can be recognized, these are believed to be
the muscle fibers possessing an intermediate stainability as revealed in the histological examination. However, further studies are required before giving any definitive conclusion on this point.</p
