## 1 Introduction  
Impaired mobility is the leading cause of reduced functionality, restricted participation levels and decreased activity levels in children and youth with severe movement disabilities, resulting in, among others, social isolation, anxiety and depression [1; 2; 3]. Introducing powered mobility wheelchairs to children with severe motor limitations has shown to improve their psychosocial and cognitive skills while increasing independence, self-exploration and intuition without any negative impact on their motor development [4]. Therefore, mobility training is of major importance starting at a young age [5]. In the child-population, cerebral palsy is the most common neuromotor disability, with a prevalence of 1.7 per 1000 livebirths [6] and is categorized into three groups: Spastic, dyskinetic and ataxic [7]. Dyskinetic cerebral palsy (DCP) is the second largest and most limiting CP group [8]. DCP is characterized by two complex movement disorders: Dystonia (i.e., involuntary movements, distorted voluntary movements and abnormal postures due to sustained muscle contractions) and choreoathetosis (i.e., chorea defined as rapid, involuntary, often fragmented movements and athetosis defined as slower and constantly changing movements) [8]. In DCP, dystonia and choreoathetosis are also present as overflow movements, defined as unintentional contractions of muscles different from the ones used during a goal-directed movement [9]. More than 70% of the DCP population presents with the highest levels of severity in gross motor functioning and fine manual abilities [10]. As a result, children with DCP are unable to use powered mobility wheelchairs with a conventional joystick, hence leaving them heavily dependent on caregivers' assistance [4; 8; 11]. Alternate steering methods such as switches or head arrays for powered mobility are proposed in literature as a way to achieve independence for children with severe gross and manual limitations [12]. In this respect, in DCP, the basal movements of the head and the feet are better controlled than the movements of the arms [8]. Therefore, clinical practice widely supports the use of a head/foot steering system as the best option to promote independent powered mobility for children with DCP, where the head movements are used to steer the wheelchair to the right and left and the feet are used to drive the wheelchair forward and backward. In general, there is little evidence supporting the best methods to train children to use a powered wheelchair and a lack of comprehensive training results in longer, time-consuming and unstructured motor learning and skill acquisition processes [4; 13]. Thus, evidence-based knowledge into the different stages of powered mobility, from learning towards self-exploration remains scarce in DCP and mobility training so far is based only on clinical expertise. To increase insights into the potential use and learning process of powered mobility wheelchairs for children with DCP, the process of learning to use it, operation of the system, the impact of movement disorders and environmental factors need to be further explored. These insights would contribute to a better understanding of the mobility limitations in this population, and assist in tailoring of better powered mobility training programs to shorten learning curves. Whereas the characterizing dystonia and choreoathetosis movement disorders seem to be the biggest limiting concepts of powered mobility in DCP [8], it is important to be able to assess the presence and severity of these movement disorders during powered mobility tasks. That is, it is stipulated that an increase in severity causes higher distortion of voluntary movements and higher presence of involuntary/overflow movements, which might result in longer and more difficult powered mobility skills training.