Laura Peeters

38 | Chapter 2 cannot be fully used to reach at the farthest distances. Slower arm movements reduce the perturbing forces exerted on the trunk induced by arm motion and, thus, require less trunk control, but they may be insufficient to complete UE tasks within certain time constraints. Reduction of arm movement speed is also seen in patients with SCI [41]. Remarkably, this strategy remains when the trunk is strapped to the backrest, which justifies the question whether it is used to minimize demands on trunk control. It may also be related to the performed UE task because, according to Fitts’ law, movement speed is dependent on the required precision of task execution [45]. To minimize center-of-mass displacement, patients with SCI use their trunk or contralateral arm to counterbalance the perturbing effect of the reaching arm [40, 41]. According to the literature, a different strategy is to change the base of support by displacing the legs and feet while sitting to increase the limits of stability [18, 34]. This strategy is primarily observed in healthy children and adults, because it is much more difficult for patients with poor motor control of the lower extremities. Proper feet positioning in a wheelchair is, therefore, extremely important to maximize the limits of stability while reaching. However, despite proper feet positioning, it may be that force transfer through the legs and feet is still different in paraparetic patients compared to healthy individuals. In most patients, trunk stability was more affected in the frontal plane than in the sagittal plane because of the smaller mediolateral base of support while sitting and the more complex reaching movements (i.e. requiring both axial rotation and lateral bending of the trunk). Patients with CP had difficulties in both respects and, therefore, found lateral reach more challenging than forward reach [30, 34, 35]. When reaching laterally, healthy children widen the distance between their feet to create a larger base of support, but particularly children with bilateral CP of the lower extremities [34, 35] and patients with SCI [38-40] have trouble to adopt this strategy, which reduces their maximal reaching distance. It should be kept in mind that for wheelchair-bound patients, even those who are able to adjust their foot position, it may not be possible to widen the base of support due to the constraints imposed by footrests. Therefore, providing additional support in the frontal plane may be necessary for sufficient trunk stability Influence of trunk support When external trunk support is given to patients with a flaccid trunk, an optimal balance should be sought between providing stability and allowing movement of the trunk. The level of support can vary based on individual needs, ranging from pelvic support to complete thoracolumbosacral orthoses, and from rigid to flexible structures [46]. Such orthoses can provide the required stability to optimize UE function in