Fig. 1

Fig. 2

Medial-lateral (upper), anterior-posterior (middle) and vertical (lower) oscillations for a male of 60 years. The ordinate represented shifts of COP in mm for medial-lateral and anterior-posterior directions and in Kg for a vertical direction. The abscissa represented a time course in sec; standing upright for the early 5 sec, knees flexion for the middle 9.5 sec, and knees extension for the last 5 sec.