Abstract

A study was conducted to investigate the discharge pattern of single motor units during submaximal prolonged activity at the tension of the recruitment threshold, and the relationship between the discharge pattern and the conduction velocity of the motor unit action potential, which has been used as an index of muscle unit characteristics (Andreassen Arendt-Nielsen, 1987). The results were as follows: 1) In all motor units observed (32 units), the spike interval during prolonged activity increased in the first several minutes. 2) Recruitment of the motor units appeared after 5 min of the load according to their recruitment thresholds. 3) In most of the motor units observed, spike intervals became shorter 15 min after the onset of the load, and the recruitment thresholds decreased immediately after the load in comparison with the value before the load. It was suggested that most units were gradually excited by this prolonged load. 4) Conduction velocity of the muscle fibers was in the range between 2.59 and 4.99 m/s. 5) When the conduction velocity of single motor units was divided into four groups according to the discharge pattern, there was no difference in the conduction velocity among the four groups. Verf.-Referat