The present study was designed to confirm the differential f atiguability between the one and two-joint muscles by the frequency analysis of the EMG activities of each pair of elbow flexors (M. biceps brachii and M. brachioradialis), knee extensors (M. rectus femoris, M. vastus medialis, and M. vastus lateralis), and ankle extensors (M. gastrocnemius and M. soleus). The results are summarized as follows :
(1) The lowering in the frequency spectra was indicated to almost the same degree between the biceps brachii and the brachioradialis.
(2) Any remarkable difference could not be detected between the lowering in the frequency spectra of the rectus femoris and those of the synergisticarlly operating one-joint muscles.
(3) When the above results were obtained, it was confirmed that the total EMG activities of the two-joint muscles tested were never smaller than those of the synergistically operating one-joint muscles.
(4) The lowering in the spectra was much more marked in the gastrocnemius than in the soleus, whereas there was little difference in the contraction level between the gastrocnemius and the soleus.
(5) It was concluded that the deep one-joint muscle was difficult to fatigue as compared with the synergistically operating superficial two-joint muscle, and that there were little significant differences in the fatiguability of the superficial one and two-joint musles.