It has been observed that the premotion silent period (p. s. p.) appears just before a rapid voluntary movement. This phenomenon is believed to be caused by one of the inhibitory discharge from the central nervous system. In the present study, the effect of p. s. p. appearance was investigated by comparing the advanced informations of the fast reactive movement (Fast condition) and the powerful reactive movement (Powerful condition) . Six healthy males aged 19-21 years were subjected to a series of experiment in which they were asked to exert their muscle strength of 15-20% of their maximum elbow extension strength. They were requested to extend their elbow joint responding to a flashing lamp as quickly as possible on the fast condition. On the powerful condition, they exerted their elbow extensor strength as greatly as possible. The EMG activities of triceps brachii and biceps brachii were recorded by bipolar surface electrodes. Mechanical response was simultaneously recorded using a resistance strain gauge transducer, and the mechanogram was analyzed on the following items: A) premotor time (the time from the signal to the onset of the force curve), B) rate of tension rise (the maximum rate of tension rise in the force-time curve) . The following results were obtained from this experiment.
1) The rate of appearance in p. s. p. on the powerful condition (21%) was significantly higher than the fast condition (9%) .
2) The premotor time on the powerful condition (180msec) was significantly later than the fast condition (160 msec) .
3) The rate of tension rise on the powerful condition (258 kg/sec) was significantly greater than the fast condition (177 kg/sec) .
It was suggested from these results that the frequency of appearance in p. s. p. on the fast condition decreased in comparison with the powerful condition. It was also considered that the appearance in p. s. p. produced the increase of the rate of tension rise.