THE RELATIVE THRESHOLD OF ACTIVATION OF SINGLE HUMAN MOTOR UNITS IN VOLUNTARY MUSCULAR CONTRACTION / 体力科学

ABSTRACT

In order to investigate the mechanism of activity of motor units, discharges of single human motor units in the m. vastus medialis in voluntary contraction by use of electrodes inserted in the muscles were simultaneously recorded with the tension developed at the knee joint in its extension effort. The results were as follows.<BR>1) The single spike discharges of single motor units were observed at the rate of 54.5-86.2%, the total number of discharges being 100%, when the knee extension effort was gradually increased and was abruptly decreased by the time of spike wave appearance on the Braun tube.<BR>2) When the tension of knee extending force was maintained steadily, the longest consecutive discharge in a single motor unit was observed for more than 90 minutes.<BR>3) The tension of knee extending force at the recruitment in a certain single motor unit recorded in 15 seconds interval was nearly constant within 30-60 minutes tested with certain fixed value for each motor unit except some fluctuation.