From walking to running: applying a dynamical systems approach to the development of locomotor skills.

Developmental transitions of complex systems may be studied by selecting (collective) variables that constrain the degrees of freedom for each developmental state. In a dynamical systems approach, the transitions from state to state are engendered through the scaling of contributing subsystems (control parameters). In this study, the locomotor skills of walking and running were compared in newly running infants by observing several likely collective variables including relative stance, estimated pathway of center of mass, and segmental/joint action. 4 children were filmed longitudinally at 5.5, 7.5, and 9.5 months of independent walking and then at 3 years of age. 3 trials per gait were selected for single stride analysis and compared with data from 4 adults. In general, the proposed collective variables showed transitional forms over the first few months of running, indicating a relatively continuous change between the 2 gait forms. Coordination of the knee joint was very similar between gaits and across age, but the ankle joint was less consistent for both gaits in the infants. Relative stance and stride length data indicated that the children could not generate vertical and horizontal displacement. These findings echo those found in newly walking infants and suggest that similar rate-limiting parameters are present for both gaits.