A longitudinal study of intralimb coordination in the first year of independent walking: a dynamical systems analysis.

Using a dynamical systems approach, we examined the development of intralimb coordination over the first year of independent walking. The segmental motion of the thigh and shank and their intralimb coordinative relationship were modeled dynamically as a system of coupled limit cycles. To test the predictions of such a dynamic model in the development of intralimb coordination, 3 infants were filmed from the onset of their first upright independent walking steps, and weekly for the next month and then every month thereafter until they had been walking for 1 year. 3 adults also were included for comparison. Analysis of the kinematic data derived from the film revealed that at the emergence of walking, the limit cycle system displayed instability in several aspects. With walking experience, however, the limit cycle regime became more attractive, such that by 3 months of walking the infants appeared to have found an adult-like stable coordinative relationship between the 2 segments. This pattern of instability followed by stability is consistent with the transitional behaviors of dynamical systems. Several potential control parameters are discussed that might contribute to the stabilization of the walking behavior. The utility of employing a dynamical systems approach for understanding developing behavioral systems is discussed.