In this phase of the electromyographic study, the discharge-intervals of single motor unit discharges (the double discharge and the single spike potential) from the hypertonic vastus lateralis muscle were analyzed by means of the Tokizane's τ-S correlation (τ: the mean discharge-interval, S: the standard deviation. As a rule, the τ-S correlation was calculated from 30 successive discharge-intervals.) and the Nomura's time-serial analysis. The discharge-interval-series analyzed were as follows (cf.: Fig. 7 in the previous report). I (continuous double discharge): successive discharge-intervals of the first spike in the double discharge II (discontinuous double discharge) The double discharge part: successive discharge-intervals of the first spike in the double discharge The single spike part: succesive discharge-intervals of the single spike potential These two parts were analyzed, respectively. Series of sufficient number of dischargeintervals were not available in II in order to be analyzed by the Nomura's method. Therefore, only the Tokizane's method was applied. III (single spike potential interspersed with doubling): successive discharge-intervals of the single spike potential discharging prior to or subsequent to doubling IV (single spike potential not interspersed with doubling): successive discharge-intervals of the single spike potential R.C. (reference control): successive discharge-intervals of single motor unit potentials obtained from the vastus lateralis muscle contracting antigravitically during standing on a fixed flat plane. Results obtained are summarized as follows. 1) τ: the τ of the double discharge was over 50-80 msec. and that of the single spike potential 25-70 msec. Generally speaking, the τ of the double discharge was longer than that of the single spike potential (Table 1). 2) τ-S correlation: First, for the convenience of comparison, the reference control curve (abb.: r.c. curve) was drawn to be a representative of the distribution of τ-S points of R.C. in the τ-S correlation diagram (Fig. 1). Over 70% of the τ-S points of the double discharge (I and II) were distributed below the r.c. curve, and, furthermore, none of the τ-S points of I, having τ more than 90 msec., fell above the r.c. curve. On the contrary, about 80% of the τ-S points of the single spike potential (II, III and IV) fell above the r.c. curve (Fig. 2). 3) The slow undulation: The amplitude of the slow undulation was lesser in I, and greater in III and IV when compared with that of the R.C. In addition, it was noteworthy that the slow undulation in IV fluctuated with a greater amplitude and an obvious period in exact accordance to the respiration, although the period of the slow undulation in others (I and III) was either obscure or irregular (Fig. 3). The mean process of the discharge-interval-series in II was step-wise, because the parts of the double discharge and the single spike were mixed in the same series and, furthermore, their τs were markedly different from each other. 4) H-type fluctuation: The occurrence of H(p) (the statistically significant period of the H-type fluctuation, α=0.05) was markedly higher in I, III and IV than in the R.C. (Table 2 and Fig. 4). 5) R-type fluctuation: Generally, most of the correlograms of I, III and IV showed the same characteristics as those of the R.C., that is, r₁ (negative) and r₂ (positive) (α=0.01). Some correlograms of III showed r₁-r₃ or r₁-r₆. On the other hand, a smaller number of correlogrms of IV had r₁ (negative) only and non-significant r₂ (Fig. 5). 6) The correlation between the discharge-interval of the first spike of the double discharge and the spike-interval, and the correlation between the spike-interval and the residual discharge-interval were not statistically significant (α=0. [the rest omitted]

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