The present study was designed to investigate the coordination of force output on the basis of the anticipation . We measured fractionated reaction times to the regularly alternating serial visual stimuli . Subjects performed the right elbOw flexion movements weighted by light and heaVy loads alternately . We exarnined the respOnses caused by unexpected break of the regularity of the stimulus and the load ( feinting stimulus ) . Premotor times and muscle activities on EMGs were discussed in

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... s of switching of force output in a rnuscle . The results may be summarized as follows : 1) Premotor time ( PMT ) to the regularly alternating stimulus ( RAS ) was shorter than that in simple reaction time . This fact suggests that the subjects anticipate the kind and timing of the next stimulus because of the alternative and periOdic stimuli . 2 ) RespOnses to the feinting stimuli ( FS ) were characterized by biphasic burst pattems on both biceps and triceps EMGs . There was the first burst of activity followed by silent periOd , and then each muscle became active again . This biphasic pattern was observed in 20% of the responses to FS . 3 ) When the biphasic burst pattern was not observed on EMGs , PMT to FS was lengthened in comparison with that to RAS 4) The first burst phase on EMG was regarded as the error respOnse caused by unexpected stimulus , and the s ond burst phase as the corr ted response ・ 5 ) The silent periOd results from a time lag between cancelation of the executing prQgram and execution of new cerrected program . 6) PMT for the heaVy load was longer than that for the light load under the simple reaction condition .