Development of locomotor balance control in healthy children.

A set of experimental studies showing how inter-segmental coordination develops during childhood in various locomotor tasks is reviewed. On the basis of these results and two functional principles (stable reference frame and control of the degrees of freedom of the body joints), we recently proposed an ontogenetic model for the sensorimotor organization of balance control in humans (5). In this model, the hypothesis was put forward that the two main modes of equilibrium control (ascending vs descending temporal organization) operate alternatively and are associated with either of two modes of head-trunk linkage ('en bloc' vs articulated) during four successive periods in the course of ontogenesis. The advantage of this model is that it is heuristic and therefore open to further improvements, including the generalization of these balance strategies to most of the posturo-kinetic activities, the comparison between unperturbed natural balance and reactions to postural disturbances. Some improvements are suggested, and are illustrated by the studies of intersegmental coordination in new experimental tasks such as hops using one foot or two feet and the initiation of gait. These new results are consistent with the idea that mastery of the degrees of freedom to be controlled simultaneously during the movement improves gradually with age. Moreover, they support the concept of multiple reference frames which operate in a complementary manner or in concert to permit the most appropriate organization of balance control, depending on the environmental requirements.