EMG obtained from muscles of lower extrimities of the normal subjects on the sinusoidally (0.3-4.0Hz) inclining board showed many complixities. So, we get Lessojous's figure of EMG and the movements of the board. Superimposed Lessajous's figures will reveal averaged patterns of EMG activities. Experiments are done in two manners of right to left to right inclination (rolling) and anterior to posterior to anterior inclination (pitching). The EMG activities of m. vastus lateralis (VL) and m. tibialis anterior (TA) increased during inclining posteriorly in 1Hz. suggesting to prevent the center of gravity moving posteriorly. Above 1Hz, the EMG activities of VL and TA seems to reveal to move the center of gravity anteriorly, being inhibited by hamstrings (HAM) and m. gastrocunemius (GS). But on rolling, EMG of HAM and TA operated during inclining below 1Hz right and left respectively, suggest to privent the center of gravity moving anteriorly and posteriorly respectively. Above 1Hz, EMG activity of right VL, right and left HAM and left TA would act to move the center of gravity posteriorly and left VL and right TA anteriorly. These suggest that the standiy posture would be stabilizted by the fluctuations of the center of gravity due to EMG activities.
