作業姿勢の筋電図的考察
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概要
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Various work postures, with special reference to some of those still practised in rural districts in Japan, were studied by the usual EMG technique. The items include: postures assumed by the subjects with different heights of work table; heaving a weight (16 kg); carrying the weight by 5 different ways (using both hands together or one hand alone, carried on one shoulder, loaded on the back, and placed on the head) ; push and pull movents; forebend postures; motions involved in the acts of standing or sitting; and long continuous standing lasting for 5 hours. The degree of muscular activity was divided into 5 classes, viz. -…no electrical discharge, ±…just perceptively active, +…definitely active, ++…strongly active, and +++…intensely active. The chief results obtained are: 1. Corresponding to the known optimal sole-distance in heaving a heavy weight, where the energy requirement becomes minimum, there appears the least electrical activity among the leg muscles (see Table 1.). 2. The electrical activities of the muscles of the upper arm, the shoulder, the neck, and the back, indicate the most favourable table height to be the height of chair +1/6 the sitting height of the subject. Incidentally it has been shown that, when the forearm is held untouched to the table, the elbow joint is kept in position by M. brachialis and triceps brachii, and the biceps contributes very little or none at all (see Table 2). 3. In holding the weight in front of the body by both hands (with arms stretched), it requires a collaboration of the extensors of the forearms, as well as that of the flexors of the foreaaarms M. biceps brachii, deltoides, trapezius, supra-spinam, infraspinam, etc. When the elbows are bent somewhat, the activities of those muscles become considerably stronger (see Table 3). 4. If the weight is held sidewa!s dy one hand, some muscles inactive in Result 3, become definitely or strongly active on the unloaded side (notably M. pectralis major, obliquus abdominis externus and iliocostalis)-a display of counterbalancing action (see Table 4). 5. The use of 'tenbinbo', the Japanese version of the yoke and carried on one shoulder lengthways, lightens generally the muscular activities, compared with the same weight carried by one hand (see Table 4). 6. The load burdened on the back involves M. serratus dorsalis cranialis and quadriceps femoris into strong activities (see Table 5). Another feature of this is the increasing activity of the abdominal muscles as the load draws near the ship 7. The ancient custom of carrying load on the head, exclusively by women, is seen today in some remote rural corners, and it requires a long training. From the standpoint of mere muscular effort, this is found to be a most efficient way to carry load-in the sense that it uses mainly those muscles employed for standing, and that it burdens them not appreciably (see Table 6). 8. In pushing much lesser number of muscles is employed than in pulling (see Table 7). 9. The forebend posture is maintained by the muscles in the back. It is noteworthy that in the deep bending those become less active, and the abdominal obliquus are called into more activities. (see Fig. 2 and Table 8). 10. The motions involved in the acts of standing or sitting were analysed in terms of individual muscular activity. M. tibialis anterior, quadriceps femoris and glutaeus maximus are found to play the leading parts, while M. soleus, the most potent member among the lower extremity in maintaining standing posture, shows no activity (see Fig. 3). 11. In long continued standing, the behaviour of the soleus was studied. There are two kinds of discharge groups to be recognized in the muscle. One group indicates its mode of discharge interval at 0.13 sec. and the other at 0.21 sec. -such was the state seen at around the commencement of standing. With the lapse of time, the rates of discharge quickened, somewhat in the former and appreciably so in the latter; and in consequence nea
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