The Effect of Perturbation Training on Reactive Balance in Children With Cerebral Palsy

Cerebral Palsy (CP), Typically Developing Children

Spastic cerebral palsy, Reactive balance, Perturbation training, Balance performance, muscle co-activation

The aim of this project was to evaluate whether perturbation training influences reflex modulation in children with spastic CP and whether changed reflex modulation leads to improved reactive balance and walking. Reactive balance was trained using rotational perturbations. Reactive balance performance and reactive muscle activity during trained and untrained perturbation conditions were assessed in children with cerebral palsy and typically developing children.

Background: With an incidence of 2 to 3 per 1000 live births, cerebral palsy (CP) is the most common cause of physical disability in children. CP is caused by a non-progressive lesion to the developing brain. The resulting inability to selectively control muscles, spasticity, and muscle weakness undermine the child's mobility and balance. Spasticity is the most common impairment in CP and is clinically characterized by increased resistance to imposed stretch to the muscle. During clinical tests of spasticity, muscles are stretched with the purpose of assessing resistance. Yet, similar stretches occur on a daily basis when balance during standing or walking is perturbed (e.g. standing on a departing bus or walking on uneven terrain). Therefore, spasticity might contribute to balance impairments that are common in CP. When standing balance is perturbed, intrinsic mechanical properties depending on muscle tone (\> 0ms), spinal reflexes leading to small changes in muscle activity (\> 50ms), and balance correcting changes (\>100-120ms after onset) contribute to restoring posture with different delays. The effectiveness of those mechanisms will depend on the ability to modulate muscle tone and reflex gains. Children with CP have increased muscle tone and reflex hyper-excitability, which might contribute to decreased balance capacities. Furthermore, the ability to modulate reflex activity is decreased in children with spastic CP compared to healthy children. This might explain why children with CP respond differently to a perturbation of standing balance than typically developing (TD) children. For instance, children with CP adopt a hip strategy at lower perturbation magnitudes than TD children. However, there is evidence that spinal reflexes can be trained in both healthy individuals and individuals with neurological disorders and that such reflex conditioning improves function, such as walking. Perturbation training has been shown to improve balance in children with CP . However, the underlying mechanisms of these improvements are not well understood. Therefore, the aim of this project was to evaluate whether perturbation training influences reflex modulation in children with spastic CP and whether changed reflex modulation leads to improved reactive balance and walking. Methods: An intervention study was performed in which children with spastic CP followed perturbation training during a 3-week period. The training consists of 9 sessions (3 sessions/week) of 30 minutes. During these sessions, balance will be trained using rotational perturbations with different magnitudes. The participant is asked to maintain balance without stepping and stay as upright as possible. Difficulty level will increase every training adapted to the subject. Before and after training, the response to muscle stretches, reactive balance (strategies) and walking performance was assessed. During the pre- and post-measurement sessions, kinematics (joint angles), ground reaction forces (GRFs) and muscle activity (electromyography, EMG) were recorded.

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