The aim of the present study is to investigate the effect of the static muscular endurance training at the lower tension level (10% maximal voluntary contraction 10% MVC) on the motor unit activity. The subject was required to develop the flex tension of right middle finger at the tension of its 10% MVC for 20 min. During the prolonged activity, surface electromyogram and motor unit action potentials were recorded from right m. Flexor Digitorum Superficialis and Prtofunds. These signals were obtained at the first day, after 2 weeks and after 3 weeks (last day) of a training period.
　The muscular endurance training program was as follows ; 1 ) sustained tension = 10% MVC, 2 ) sustained duration 20 min, 3 ) training frequency = one practice/day and 6 practices/week, 4 ) training period = 3 weeks.
　Obtained results were as follows :
　1 ) Amplitude of surface electromyogram during the prolonged activity increased gradually for 700% of initial amplitude. But the rate of increase was decreased depend upon the period for training.
　2 ) Before the training, recruited motor units fired continuously during the activity. At a period of 2 weeks of the training, some motor units fired intermittently (decruited and re-recruited) were appeared and its tendency was more obviously at 3 weeks training period.
　3 ) With detraining for 1 month, discharge pattern of motor units returned to initial pattern (pattern of first day of the training). And with re-training for 2 weeks, motor units showed the same discharge pattern as the pattern resulted from the first training program. The training effect on the motor unit activity was highly reproducible.

DESCENTE SPORTS SCIENCE Vol.14/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE