Laura Peeters

12 | Chapter 1 children, interaction between the trunk and the UE develops with age due to maturation [7, 11]. Thus, when trunk function becomes impaired in early life, it may affect general motor development. Second, children are more prone than adults to develop spine deformities due to muscle weakness as long as the spine is growing. These deformities also affect trunk movement and stability [12]. Spinal deformities are often seen in patients with neuromuscular disorders (NMD), like SMA and DMD, and are related to factors such as type of SMA and age at loss of ambulation [13, 14]. As the trunk is indispensable for performing seated daily tasks, trunk impairment will likely result in changed interactions between trunk, UE and head movements when performing such tasks or even in an inability to perform certain tasks. However, knowledge of reduced motor capacity to perform seated activities is scarce, especially in patients with NMD (Chapter 2). Research has shown that UE function gradually decreases in patients with DMD and SMA over time [15, 16]. Therefore, trunk movement might gradually increase to compensate for reduced arm function when performing seated tasks. On the other hand, trunk impairment might also lead to an incapacity to maintain postural stability and control center-of-mass displacements when performing voluntary UE movements, leading to decreased task performance. Since most of the patients with DMD, as well as patients with symptomatic SMA in early childhood, will not be able to walk once they have reached adulthood, it is of utmost importance to gain more insight in the interactions between trunk, UE and head movements when performing seated tasks. This knowledge is essential for developing dynamic assistive devices for the trunk and the head to support people with NMD in performing daily tasks. Clinically applicable dynamic devices for the trunk do not yet exist and are scares for the head. Development of a dynamic trunk and head assistive devices that could be integrated with an arm assistive device in the future was the key aim of the Symbionics project (Box 1). The focus of this thesis is on trunk function in two types of NMD: DMD and SMA. These neuromuscular disorders are described below. Duchenne muscular dystrophy DMD is an x-linked, recessive neuromuscular disorder with an incidence of approximately 1 in 6000 live male births.[9] DMD is characterized by symmetrical, progressive muscle weakness, caused by the lack of the dystrophin protein in the muscle cells [17]. Proximal muscles are affected earlier than distal muscles (Figure 2a), resulting in a mean loss of ambulation around 11 years with the use of corticosteroids in The Netherlands [18]. UE function is already decreased in the early disease stages of DMD and overhead reaching is lost around the same age as ambulation is lost [15, 19]. The life expectancy is reduced to approximately 30 years on average [20]. Since