Organization of lateral balance control in toddlers during the first year of independent walking.

The authors of the present study tested the hypothesis that toddlers initiate lateral body stabilization first at the hip level in order to better control the center of gravity (CG), minimize the upper body destabilization induced by the movement of the feet, and prevent falls. Intersegmental coordination among the hip, the shoulder, and the head was investigated in toddlers during their 1st year of independent walking. The efficiency of locomotor balance control was examined in the frontal plane. An automatic optical TV image processor (ELITE system) was used in analyzing the kinematics of foot, hip, shoulder, and head rotations. For the hip, the shoulder, and the head, appropriate anchoring indices were defined so that comparisons could be made concerning the stabilization of a given body segment with respect to its external space and to the adjacent supporting anatomical segment. Cross-correlation functions were also used for extracting the temporal patterns of the body segments that occurred during locomotion and for obtaining some information about the coupling of 2 consecutive segments such as the head-shoulder and the shoulder-hip. First, hip stabilization in space appeared from the 1st week of independent walking and clearly preceded those of the shoulder and the head, suggesting an ascending progression, with age, in the ability of new walkers to control lateral balance during locomotion. Second, the hip movements occurred before the shoulder movements and the shoulder movements before the head movements, indicating that locomotor balance control is organized temporally in an ascending fashion, from the hip to the head. Third, the high values of the correlation coefficients, mainly between the head and the shoulder, were consistent with a global en bloc operation of the head-trunk unit.