Fig. 4

Upper 9 graphs showed power spectra of COP oscillations for all subjects, during standing upright （upper 3 graphs）, knees flexed （middle 3 graphs） and knees extension （lower 3 graphs）. The left column showed spectra for a medial-lateral direction, the middle column showed spectra for an anterior-posterior direction, and the right column showed spectra for a vertical direction. The abscissa represented frequency in Hz, and the ordinate represented powers of the oscillations. 　Lower 6 graphs showed normalized power spectra of COP oscillations during knees flexed （upper 3 graphs）, and knees extension （lower 3 graphs） for all subjects. The left column showed the oscillations for medial-lateral direction, the middle column showed those for anterior-posterior direction, and the right column showed those for a vertical direction. The abscissa represented frequency in Hz, and the ordinate represented the powers of oscillations in dB.