Abstract
In order to clarify the voluntary strength control mechanism, certain characteristics of motor units were studied after series of recordings were simultaneously made on the discharge of single motor unit in the m. vastus medialis in its voluntary contraction by use of electrodes inserted in the respective muscle and the tension developed when attempting to extend the leg at the knee joint. The results obtained were as follows:
1) When analyzed from the relationship between discharge interval and its standard deviation, unit of other type which may be classified as“intermediate”unit than kinetic and tonic units as previously classified, was found.
2) The mean value of muscular tension was found to be proportionate with value of standard deviation, when tension made by recruitment of motor unit was measured by 15 seconds interval. While the K unit was found to be of low threshold value, T and M units were found to be of high values.
3) No consistent relationship was found between the mean value of relative threshold and the frequency of single spike appearance, while K unit showed a tendency of smaller rate of single spike appearance than T unit.
5) A decreasing tendency was generally observed in the mean value of relative threshold and its standard deviation, by loading isometric muscle tension of 2-10kg for 3-10 minutes. The rate of single spike appearance also deceased by same loading.
