MOTOR UNIT POTENTlAL PARAMETERS OF MUSCLE IN NORMAL CHINESE

The duration and voltage of motor unit potential at weak voluntary effort, as well as the peak voltage at the maximal voluntary contraction of in deltoid, biceps brachii, first dossal interosseous, quadriceps femoris and tibialis anterior were measured in 178 normal Chinese subjects of different ages. In this study, concentric electrodes with an external diameter of 0.45mm were used for leading off, the amplification was 100μV/cm and the time base was 5 ms/cm. Of each muscle the mean values were caculated from twenty motor unit potentals. The results were estimated statistically and by the aid of the computer, showing that the duration of motor unit potentials increased with age, more markedly before 15 years of age, in the first dossal interosseous, biceps brachii, quadriceps femoris with further increase every five years, whereas in deltoid, tibialis anterior the change was significant up to 15—20 years of age and then further increased in middle age and old age in deltoid but remained unaltered in the tibialis anterior. There was a difference in various muscles, in the same age group, having a longest duration in the tibialis anterior, a shortest in the first dossal interosseous.
Although the mean voltage also increased with age, the increase was not so marked as that of the duration. It can manifest during two periods of age, The correlation between the peak voltages of motor unit potentials at maximal contraction is not so simple as mentioned above, The value is bigger in children and elderly persons than in the youth.