ヒトの骨格筋における筋繊維型の変化

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  • Fiber type transformation in human skeletal muscle.
  • ヒト ノ コッカクキン ニ オケル キンセンイガタ ノ ヘンカ

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In order to assess the possibility of fiber type transformation in human skeletal muscle, muscle fiber composition of athletes in various events, raining-induced changes in muscle fiber, fiber type distribution in the course of development and ageing, and the results of cross-innervation and chronic artificial stimulation in animal muscle experiments are reviewed.<br>The present available evidence suggests that fiber type transformation may take place in human skeletal muscle, although genetic factors appear to play essential roles in determining muscle fiber composition. Endurance training or activities of daily living may be capable of converting fasttwitch-glycolytic type II B fibers into fasttwitch-oxidative-glycolytic type II A fibers, and then into slow-twitch-oxidative type I fibers. This may explain why endurance-trained muscles have a higher percentage of type I fibers and lower percentage of type II B fibers as compared to untrained or power-trained muscles. The variation in the proportion of type II A fibers observed in endurance-trained muscles is probably due to differences in the degree of training. Most of the longitudinal studies have failed to show changes in muscle fiber composition with endurance training. This may be ascribed to too short training period, since the fiber type changes only after long periods of stimulation as shown in chronic stimulation experiments in animal muscles. It is postulated that type II C fibers, which are normally rare, are transitional type between type I and II A fibers. This could account for the presence of type II C fibers in the muscles of endurance athletes. The changes induced by endurance or activities of daily living are reversible: the conversion of type I to type II B via type II A fibers occurs during detraining or immobilization. Increased proportion of type I fibers with age and decrease in the relative occurrence of type I fibers in very old age are most likely related to physical activity levels.<br>Excepting the reversion of type I to type II fibers produced by detraining or inactivity, a transformation of type I to type II fibers seems to be difficult to achieve, judging from the results of animal experiments and training experiments in man. The athlete's success in power events appears to depend more on the genetic endowments in com parison with that in endurance events. However, there is a possibility of conversion of type I to type II fibers. The training methods to increase the occurence of type II fibers will require further investigation.<br>Smoking, undernutrition and throid Status may also have influences on muscle fiber composition.

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  • 人類學雜誌

    人類學雜誌 94 (1), 1-18, 1986

    一般社団法人　日本人類学会

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