Development of a kinematic coordination pattern in toddler locomotion: planar covariation

The purpose of this study is to analyze the coordination patterns of the el evation angles of lower limb segments following the onset of unsupported wa lking in children and to look for the existence of a planar covariation rul e as previously described in adult human locomotion. The kinematic patterns of locomotion were recorded in 21 children (11-144 months of age) and 19 a dults. In 4 children we monitored the very first unsupported steps. The ext ent to which the covariation of thigh, shank, and foot angles was constrain ed on a plane in 3D space was assessed by means of orthogonal regres sion a nd statistically quantified by means of principal component analysis. The o rientation of the covariation plane of the children was compared with the m ean value of the adults ' plane. Trunk stability with respect to the vertic al was assessed in both the frontal (roll) and sagittal (pitch) planes. The evolution with walking experience of the plane orientation and trunk oscil lations demonstrated biexponential profiles with a relatively fast time con stant (<6 months after the onset of unsupported locomotion) followed by a m uch slower progression toward adult values. The initial fast changes of the se walking parameters did not parallel the slow, monotonic maturation of an thropometric parameters. The early emergence of the covariation plane orien tation and its correlation with trunk vertical stability reflect the dynami c integration of postural equilibrium and forward propulsion in a gravity-c entered frame. The results support the view that the planar covariation ref lects a coordinated, centrally controlled behavior, in addition to biomecha nical constraints. The refinement of the planar covariation while morpholog ical variables drastically change as the child grows implies a continuous u pdate of the neural command.