Kinematics and postural muscular activity during continuous oscillating platform movement in children and adolescents.

The aims of this study were to (1) characterize anticipatory and reactive postural strategies in typically developing (TD) children and adolescents; (2) determine if TD youth shift from reactive to anticipatory mechanisms based on knowledge of platform movement; and (3) determine whether TD youth further modify postural strategies when additional information about the perturbation is provided. Sixteen typically developing youth aged 7-17 years stood with eyes open on a movable platform that progressively translated anteroposteriorly (20 cm peak-to-peak) through four speeds (0.1, 0.25, 0.5, and 0.61 Hz). Participants performed two trials each of experimenter-triggered and self-triggered perturbations. Postural muscle activity (1000 Hz) of the tibialis anterior, gastrocnemius, quadriceps and hamstrings and 3D whole body kinematics (100 Hz) were recorded. The Anchoring Index and marker-pair trajectory cross-correlations were calculated as indications of body stabilization. The number of steps taken to regain balance/avoid falling were counted. Transition states and steady states were analyzed separately. Generally, the higher frequencies resulted in more steps being taken, lower correlations coupled with greater temporal lags between marker trajectories, and postural muscle activity similar to older adults. The provision of self-triggered perturbations allowed participants to make the appropriate changes to their balance by use of anticipatory postural control mechanisms.