Fig. 2. Kinematics of the pendulum mechanism. (A) Schematic representation of the inverted pendulum: the hip vaults over the stance limb. (B) Ensemble averages (± S.D., N=5 steps) of vertical hip displacement (GT_y) and knee joint angle in children of different age, and in a representative adult walking at two different speeds (right panels). Data are plotted vs the normalised gait cycle. Each record begins with the right foot strike. GT_y is expressed in relative units (normalised by the limb length L). (C) Percent of variance (± S.D.) of GT_y data explained by the second Fourier harmonic is plotted as a function of the time after the onset of independent walking. The values for the adult group were obtained by computing the mean (± S.D.) from the pooled data obtained for walking at natural, freely chosen speed (on average, 3.8±0.4 km h^–1). (D) Correlation coefficient between GT_y data in children and the corresponding ensemble average in adults during stance. For both C and D, the time course of changes with age was fitted by an exponential function (r=0.93 and 0.87 in C and D, respectively). , the corresponding time constant.