We investigated the quantitative relationships between two basic MUAP parameters-amplitude, duration- and motor units recruitment thresholds of first dorsal interossei (FDI), biceps brachii (BB), rectus femoris (RF) and tibialis anterior (TA) muscles in young 5 healthy male subjects.
MUAPs were collected in each muscle, using a concentric needle with a quadrifilar electrode which we recently developed, during 10 seconds voluntary isometric contraction. During the first 5 seconds, the contraction force was increased from 0 to 50% maximal voluntary contraction (MVC) by adding 10% MVC every second. The maximal force of 50% was maintained for the last 5 seconds. MUAP analysis was performed using the EMG signal decomposition technique developed by De Luca and colleagues.
As a result, 553 MUAPs (FDI 203, BB 148, RF 91, TA 141) were obtained. In each muscle, both amplitude and duration had significant positive correlation (more than 0.7, p<0.01, Kruskal-Walis test) with the motor units recruitment thresholds. A comparison among the four muscles on amplitude found that BB has the smallest, and RF is smaller than other two muscles (p<0.05, sign test). On duration, FDI has the smallest (p<0.05, sign test), and the other three muscles have no significant difference from one another. It is concluded that the size principle can be detected in the concentric needle EMG, and in clinical examinations, we need to pay much attention to patients' contraction force.

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Cross-sectional areas of paravertebral muscle in 80 stroke hemiplegics were measured, using computed tomography. The paravertebral muscles at the levels between L3 and L4 and those of the gluteus medius between L5 and S1 were surrounded with a track-ball. Then the area of the pixels that have CT value more than 30 and less than 120 HU in the surrounded area were divided by the trunk cross-sectional area at L3, whose value is called Muscle%-area. The Muscle%-area of the paravertebral muscles showed no significant differences between the contralateral side to cranial lesion and the ipsilateral side in 71 patients. Nine patients, who had smaller ipsilateral Muscle%-area of the paravertebral muscles, denoted the following similar patterns: (1) severe degree of motor impairment; (2) more than 90 days since stroke onset; and (3) very slow walking (less than 1m/sec).

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Differences between right and left handwriting were analysed in twenty right-handed normal subjects. The subjects were asked to write a Japanese character of syllabary in squares of three different sizes (1×1, 5×5, and 15×15cm) on a digitizing tablet using the right and left hands alternately. Writing was done ten times for each size, and a total of 60 writings for each subject were recorded in a computer memory. Twelve indices were defined for each writing so that kinematic and morphocinetic differences between the hands might be revealed. A linear discriminant analysis between writings by the right and left hands showed better discrimination in the smaller than larger writings, that was as accurate as the discrimination by visual evaluation of the character shape. The indices showing fluctuation of the pentip acceleration and of the shape deviation were of special value for the discrimination. Size of daily writing is as small as within 1×1cm. That may lead to proficiency in smaller writing with the right hand reflecting the better discrimination by the discriminant function in this study.

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