Laura Peeters

84 | Chapter 4 the DMD participants, while trunk extension was seen in the other tasks. Lateral bending was mainly performed towards the non-dominant side, in other words opposite to where the arm was lifted for reaching, except for far lateral reaching. Axial rotation was performed towards the dominant side when reaching laterally and towards the non-dominant side when reaching forward and contra-laterally. The movement direction for DMD participants was essentially the same as in the HC. Normalized muscle activity was significantly higher in all muscles and all tasks for DMD patients compared to HC (Figure 4, Additional file 4). Static sitting (without back or armrests) already required approximately twice as much of trunk muscle capacity in DMD patients than in HC. The ability to perform a task was related to the percentage of muscle capacity used. This could for example be seen when comparing reaching forward without object and with a 500 gram object (Figure 4, Additional file 4). All DMD patients with Brooke scale 1 were able to perform the task with a 500 gram object, but only half of the DMD patients with Brooke scale 2 and none of the subjects with Brook scale 3 could. However, those patients with Brooke scale 2 needed around 100% of their back and arm muscle capacity to execute the task. DISCUSSION This study provides new insights in the role of trunk movements and used muscle capacity in DMD patients when performing seated tasks. During arm tasks the trunk shows a larger range of motion in DMD patients compared to healthy controls, combined with increased normalized trunk muscle activity. This reflects that due to compensatory movement, demands on trunk muscles are increased which is compounded by trunk muscle weakness. Both maximum active trunk ROM and maximum trunk joint torque were significantly decreased in DMD patients compared to HC, indicating that their overall trunk capacity is already less compared to HC. Although this finding is not surprising, this is the first study to show it in a quantitative manner. However, the limitations found in maximum ROM are unlikely to result in restrictions when performing tasks such as tested here, because the maximum trunk ROM (Figure 1) was less than generally used to perform daily tasks (Figure 2). Interestingly, we found that boys in early disease stages (e.g. Brooke scale 1) already showed lower trunk joint torque compared to HC. Additionally, trunk joint torque (in Nm) did not significantly decrease with Brooke scale, while shoulder abduction torque did. The latter was also found in previous research [4]. This could indicate that arm function (i.e. Brooke scale) is decreasing first or that the decrease in trunk function is independent of the decrease in arm function. However, as bodyweight