抄録
It has been observed that the tonic discharge disappears just before a rapid voluntary movement. It is supposed that this phenomenon is caused by some inhibitory discharges coming from the center in the brain or from the brain stem to the motoneurons in the ventral horn cell of the spinal cord. In the present study, the relationship between the degree of experience in sports and the rate of appearance in the premotion silent period was investigated on 81 healthy subjects ranging in ages from 18 to 25 years old. The subjects were divided into three groups by their experiences in sports: Group A: nonathletes, Group B: students who were athletes at junior and/or senior high school, Group C: athletes who were trained from junior high school to college. The subject was requested to exert his muscle strength for two to five second at a rate of 15 to 20% of the maximum elbow extensor strength. After that, the subject was asked to respond to the flashing lamp as quickly as possible by extending his elbow joint. The EMG activity from triceps brachii was led off by bipolar surface electrodes, and the mechanical response was simultaneously recorded with resistance strain gauge transducer. The following results were obtained from this experiment: 1. There were two types of premotion silent period (p.s.p.) : "complete" and "incomplete". 2. The rate of appearance in the complete p.s.p. and total p.s.p. (complete p.s.p. plus incomplete p.s.p.) became greater in proportion to the degree of experience in sports. 3. The number of subjects who showed relatively high rate of appearance (over 51%) in the p.s.p. increased in the order of Group A, B and C. 4. There was no difference between left and right triceps brachii in the rate of appearance in the p.s.p.
