Differences of surface myoelectric signal and its low and high frequency components during growth in elementary school children

Abstract

In this study, we investigated the applicability of the analyzing method of surface myoelectric signal proposed by Kamo & Morimoto (2000) for children's (age groups: Grade 2, 4, and 6 of elementary school) monopolarily recorded surface myoelectric signal from m. vastus medialis. The subjects (n=16) were requested to exert constant brief (10 sec) isometric knee extension at low tension (4-12%MVC). Next, to elucidate the age dependent change of the possible motor control mechanisms, the change of the contribution of the integrated value of low (LFC) and high frequency component (HFC) to integrated value of raw signal was tested. Index of the contribution was considered from the slope of the regression line between raw and LFC integrated values, and between raw and HFC integrated values. Obtained results were as follows: 1. Turning frequency (TF) appeared in the children's amplitude spectrum of surface myoelectric signals. And TF shifted toward higher frequency depending upon the developed tension. 2. For children, cross-correlation analysis characterized LFC as conducting, and HFC as non-conducting characteristics. 3. There was no significant difference in integrated value of raw signal between age groups at each target tension. Results were similar concerning LFC and HFC as well. 4. The comparison of regression slopes showed that HFC had significantly lower contribution to construct the raw signal than LFC. Furthermore, results showed no age related difference as far as the contribution of the LFC, HFC to the raw signal concern. Results 1 and 2 were in good agreement with the results obtained from university-students (n=5). Therefore, it suggests that the analyzing method proposed by Kamo & Morimoto (2000), can adapt to the myoelectric signal from children. Similar result between the age groups suggests that under low-tension brief contraction motor unit control mechanism showed no developmental stage difference from 2 nd grade to university student, yet muscular strength of the 2 nd grade did not reach to the university student level.