Transcranial magnetic stimulation of human motor cortex during voluntary muscle contraction produces motor evoked potentials followed by a transient electromyographic silent period(SP). SP has been known to `inhibitory' effects of cortical activity.

We evaluated SP in abductor pollicis brevis muscle in 21 healthy adults(male: 11, female: 10) who have no neurological signs and symptoms.

SP in relation to sex, recording site (right-left difference), height, magnetic stimulation intensity, and voluntary muscle contraction were studied.

We concluded as follows

1) The SP of male subjects was significantly longer than that of female subjects.

2) There was no significant difference of SP according to recording site and height.

3) The SP was significantly prolongated with increasing magnetic stimulation intensity.

4) There was no significant difference of SP duration between maximal and submaximal voluntary muscle contraction.