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

Reactive and anticipatory postural activity has been described in single discrete perturbations in youth with cerebral palsy (CP) but not in continuous perturbation situations.

We sought to determine how the ability to control postural responses (as reflected in the number of steps taken, postural muscle activity, and marker-pair trajectory cross-correlations) compares between typically developing (TD) youth and age-matched youth with CP when exposed to various frequencies of continuous platform oscillation. We also sought to determine if youth with CP could further modify postural activity based on knowledge of platform movement.

Eleven youth with CP and sixteen TD youth aged 7-17 years stood with eyes open on a movable platform progressively translated antero-posteriorly through four speeds in experimenter-triggered and self-triggered perturbations. Postural muscle activity and 3D kinematics were recorded. The Anchoring Index and marker-pair trajectories were used to quantify body stabilization strategies. Transition states and steady states were analysed. Mann Whitney-U tests analysed between-group differences at each frequency.

At lower frequencies (0.1 and 0.25 Hz) youth with CP behaved like age-matched TD controls. At higher frequencies (0.5 and 0.61 Hz), youth with CP took a greater number of steps, had a preference for stabilizing their head on the trunk, had low marker-pair correlations with high temporal lag, and showed increased tonic activity compared to their TD peers.

Higher frequency platform movements proved more difficult for youth with CP, however, like TD youth, they shifted from reactive to anticipatory mechanisms when the platform frequency remained constant by taking advantage of knowledge of platform movement. When given control over perturbation onset, further evidence of anticipatory mechanisms was observed following the transition to a new oscillation frequency.