Abstract
The effects of contraction strength on the power spectrum of surface electromyogram (EMG) were studied during isometric contration of elbow flexion. Seven subjects sustained weights ranging between 2 kg and nearly maximum voluntary contraction strength at the wrist at the elbow joint angle of 90 degrees. Surface EMG of muscle biceps brachii was transfered to frequency power spectrum. The power spectrum was divided into four parts by the effects of contraction strength : below 50Hz, 50-80Hz, 80-120Hz and over 120Hz. With the increase of contraction strength the relative power below 50Hz decreased significantly, the relative power between 50HZ and 80Hz tended to increase, the relative power between 80Hz and 120Hz tended to decrease, and the relative power over 120Hz showed unstable changes. The effects of contraction strength below 120Hz were explained connecting with the activity level of motor units and the synchronization level of motor units activities. The relative power over 120Hz was connected with the shape of individual spike of surface EMG.
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