Fig. 6. Inter-segmental coordination. (A) Ensemble averages (± S.D., N=5 steps) of thigh, shank and foot elevation angles in children of different age and in a representative adult. (B) Corresponding gait loops plotted in 3-D. A loop represents one gait cycle and is obtained by plotting the thigh waveform vs shank and foot waveforms (after mean values subtraction). Paths progress in time in the counter-clockwise direction, foot strike and lift-off corresponding approximately to the top and bottom of the loop, respectively (swing phase is in red). The interpolation planes result from orthogonal planar regression. The first eigenvector (u₁) is aligned with the long axis of the gait loops of B, the second eigenvector (u₂) is aligned with the short axis, and the third eigenvector (u₃) is the normal to the plane. u_it, u_is and u_if correspond to the direction cosines with the positive semi-axis of the thigh, shank and foot angular coordinates, respectively. (C) Changes with age of percentage of variance accounted for by u₁, u₂, and u₃ (PV₁, PV₂, PV₃ respectively). (D) Direction cosines of the plane normal. (E) Step-by-step variability of the plane normal (exponential fitting, r=0.91).