Laura Peeters

General discussion |123 6 of the legs to bodyweight support between DMD patients and HC when sitting quiet and lifting the arms, but we did find a significant decrease in contribution of the legs in DMD patients when reaching beyond arm’s length, even though only 3 of the 9 boys with DMD were non-ambulant. Further research should clarify whether differences were indeed related to leg muscle weakness, or that weakness of the trunk or UE also played a role. Measurements should combine ground reaction forces with leg and trunk muscle activity, and a trunk stability measurement, to determine the passive/active contribution of the legs and to see how this relates to trunk stability. Notably, even the non-ambulant patients were still able to increase the force on their feet. Whether this is only a passive support from the legs or also an active contribution needs to be determined in further research. Clearly, irrespective of the question whether these forces are active or passive, these findings show that proper feet support while sitting in a wheelchair is necessary. Implications for interventions This thesis showed that the trunk in DMD and SMA patients is much weaker than it appears at first sight. Although the included patients could sit independently (without backrest) and were able to perform several arm tasks at the same time, trunk strength was strongly decreased and trunk muscle effort was much higher compared to HC. This means that clinical interventions with regard to trunk function might be required to start earlier than what would be expected based on the observable decline in trunk function. Physical activity and seating Physical and muscle strength training has beneficial effects on muscle strength and fatigability [30, 31]. Even if people become wheelchair dependent, physical training can be beneficial to reduce the deterioration caused by disuse [31]. Seating adjustments can be another way to reduce fatigue in wheelchair users. A proper seating cushion combined with proper back- and armrests should provide the opportunity to relax the muscles when seated in a wheelchair. Additionally, it is also important for prevention of pressure points and improving sitting stability when necessary [32]. The latter is often done by stabilizing/fixating the pelvis first in order to create a stable base for UE task performance. However, as also mentioned by Sprigle, et al. [33], providing stability with wheelchair cushions or a sitting orthosis undermines the ability to move the trunk and pelvis to perform daily tasks (chapter 3) and additionally to prevent disuse. A good balance between providing stability and allowing movement needs to be sought to optimize task performance. Therefore, more research is needed into both potential benefits and negative effects of stabilizing the pelvis and restricting trunk