Laura Peeters

122 | Chapter 6 might mask focal impairments or compensatory mechanisms. Clinical assessment of individual trunk levels could be done with the use of the Segmental Assessment of Trunk Control [24]. However, some adjustments have to be made when used in patients with DMD and SMA, because the trunk control score is automatically zero if people cannot keep the UE in shoulder abduction [25]. When the aim is to study specific trunk movements or to develop devices or interventions, it is recommended to separately assess several trunk segments and the pelvis. Trunk as central segment Interaction with head Head movement is strongly related to trunk movement as was discussed in chapters 2 and 3. We measured head movements in DMD and SMA patients as well, but chose not to incorporate these results in chapters 4 and 5, as this would have led to complex and elaborate manuscripts. DMD and SMA patients are able to move their head until in the late disease stages, despite neck flexor weakness already present in early disease stages [7, 8]. In our population, neck muscle weakness was evident in the reduced maximum neck ROM in all movement planes for SMA patients and in extension and axial rotation for DMD patients. However, all but one SMA participant did not seem to be restricted in head movement when performing the tasks (restriction in head movement in this SMA participant was caused by spinal fusion up to cervical levels). Neck muscle weakness negatively influences head stability probably earlier than the loss of ability to move the head. This is especially noticed by patients when moving in a car or wheelchair over uneven surfaces. Additionally, decreased trunk stability also challenges head stability, as previously reported for patients with CP [26]. Interaction with lower extremities The lower extremities play an important role in sitting stability [10]. A larger base of support is created with the feet on the floor, resulting in increased limits of stability and therefore increased workspace [27]. Feet position is also adapted by healthy children and adults to meet specific task demands in terms of stability [28]. Moreover, even if the feet remain in place, the leg muscles are actively involved in performing seated tasks [10, 29]. Therefore, in patients with neuromuscular disorders with early leg muscle weakness, impaired contribution of the lower limbs to trunk stability can be anticipated. However, the impact of such impairment is unknown. We performed a first pilot study with 9 healthy boys and 9 boys with DMD to see if we could detect a difference in contribution of the legs to bodyweight distribution between both groups while sitting quietly, lifting the arms and reaching forward. We used a force plate to measure the ground reaction forces and found no difference in contribution