CERTAIN CHARACTERISTICS OF MOTOR UNITS OF ARM MUSCLES
1973 Volume 22 Issue 1 Pages 9-16
Details
1973 Volume 22 Issue 1 Pages 9-16
In order to investigate certain characteristics of activity of motor units during strength control, discharges of single human motor units in the m. biceps brachii by use of electrodes inserted in the respective muscle were simultaneously recorded with tension developed at the elbow joint in its flexion effort. The results obtained were as follows :
1) When analyzed from the relationship between mean discharge interval of motor unit and its standard deviation, unit of other type which may be classified as “intermediate” (named “M”) unit than kinetic (K) and tonic (T) units as classified by previous workers was also found to be similar to that of leg muscles.
2) The tension produced by elbow flexion effort at the recruitment in a certain single motor units recorded in 15 seconds interval was also nearly constant during the 20 minute long experimental period which coincided with the result obtained in the case of leg muscles.
3) On the relationship between mean relative threshold of motor unit and its standard deviation, while the T unit was found to be of low threshold value, the K and M units, recording higher values than the case of T unit in most occasions, showed wider range in its values. After analyzing the relationship between the values of T and K/M units by use of a diagram, standard deviation of relative threshold was found to be larger in relation to its given mean value in the dominant arm than the recessive. No significant differences were found in the size of error in attempting to continue certain muscular tension with control between the dominant and recessive arms.
4) Statistically significant differences at 5% level confidence were found between different individual subjects in the frequency of single spike, appeared and recorded, ranging between 25.0-97.5 percent. The subject who showed higher single spike appearance frequency than the other was found to react significantly quickly in his single reaction time responding to photic stimulus (1% level) . Higher frequency of single unit spike appearance was observed in T unit than in K unit.
