幼児の短時間および持続的等尺性収縮における表面筋電図の周波数および振幅の分析
1984 年 29 巻 2 号 p. 115-123
詳細
1984 年 29 巻 2 号 p. 115-123
The purpose of the study was to compare the electromyographic characteristics between children and adults during isometric contractions. The subjects in this study were eight children (male, 5.8yr)and nine adults (male, 22.5yr). They were asked to exert respective brief isometric elbow flections at the strength of 20, 40, 60, 80% MVC, and then to sustain it at the strength of 60% MVC to exhaustion. The surface EMG was recorded from m. biceps brachii. EMG power spectrum, its median frequency and mean amplitude were computed from the recorded EMG. The results were as follows: 1. The median frequencies in children and adults varied little in accordance with the change of strength, the former being l0 to 14 Hz lower than the latter. The difference was significant at 20,40, 60% MVC (p<0.05) and 80% MVC (p<0.01). Amplitudes in adults were higher than those in children. The former showed exponential increment with the increase in strength in contrast to the latter which increased linearly and more gradually. 2. During sustained isometric contractions median frequencies in adults showed rapid linear decrement with time, but those in children decreased more slowly. In consequence, a significant difference in the median frequencies was observed at 80% (p<0.05) and l00% (p<0.01) of the duration in contraction. Amplitudes in adults were larger than those in children. The former increased gradually with time , but the latter showed no temporal change. 3. It seemed that the differences of EMG frequency and amplitude between children and adults during brief isometric contractions were caused by the difference in conduction velocity due to different muscle fiber diameters, and that the change in EMG during sustained isometric contraction was influenced by muscle lactate concentration and/or synchronization of motor units. It was concluded that the dominance in lower frequency components of EMG were evidenced in children during brief isometric contractions, and that EMG frequency components in adults lowered more rapidly with time than those in children during sustained isometric contraction.
