Increasing motor variability facilitates motor learning of trunk postural control during sitting in children with cerebral palsy.

The goal of this study was to determine whether increasing motor variability by applying varied perturbation forces to the pelvis during sitting astride would facilitate motor learning of improved trunk postural control in children with cerebral palsy (CP). Fourteen children with spastic CP participated and were tested in two conditions: CONSTANT and VARIED force perturbations. Each condition consisted of a 15-minute session. A custom robotic system delivered repetitive perturbation forces to the pelvis while participants sat astride. To assess changes in postural control, unpredicted perturbations in the anterior and posterior directions were applied before and after each repetitive perturbation session. The kinematics of head, trunk, and pelvis movement and muscle electromyography were recorded. The results showed that one session of pelvis perturbations with either the CONSTANT (P = 0.028) or VARIED force magnitudes (P = 0.009) led to an earlier onset of trunk extensor activation in response to unpredicted perturbations. Further, one session of perturbations with VARIED force magnitudes but not the CONSTANT magnitude induced a significant decrease in peak angle of head extension (P = 0.016) and an improvement in onset order of the neck and trunk muscle activation under unpredicted perturbations (P = 0.020). These findings suggest that repeated pelvis perturbations during sitting astride may induce an improvement in reactive trunk postural control in children with CP. Further, increasing motor variability by applying VARIED perturbations may be more effective than the CONSTANT perturbations for promoting motor learning of improved head stability and trunk postural control in children with CP.NEW & NOTEWORTHY Many children with cerebral palsy (CP) exhibit impairments in trunk postural control, particularly the second level of postural control. Results from this study suggest that applying repeated pelvis perturbations during sitting astride may induce an improvement in reactive trunk postural control in children with CP. Further, increasing motor variability by applying repeated VARIED force perturbations may be more effective than the CONSTANT perturbations in promoting motor learning of improved head stability and reactive trunk postural control in children with CP.