Laura Peeters

Trunk involvement in performing upper extremity activities | 33 2 at which postural deficiencies were observed [29]. Differences in postural stability between different types of CP were also found by Heyrman, et al. [35]. Children with bilateral CP of the lower extremities were less impaired in terms of trunk stability, compared to those with bilateral CP of the lower and upper extremities. Children with bilateral CP of the lower extremities had only minor problems of static sitting balance, whereas children with bilateral CP of the lower and upper extremities had significantly impaired postural control while sitting. Children with bilateral CP of the lower limbs had more difficulties when reaching laterally compared to reaching forward [35]. In people with SCI, trunk movement and stability during reaching has been studied by a few research groups [37-41]. Patients with SCI (injury level C7-L4) adapted their trunk and arm movement strategies mainly to maintain trunk stability [40, 41]. Both arm and trunk movement paths were less straight and the peak speed was much lower compared to healthy adults [41]. The reduction in movement speed remained when the back was strapped to the backrest. When reaching forward to near targets, trunk extension was seen in some patients with SCI (injury level T4-L4) [40], whereas reduced trunk flexion was seen compared to healthy adults when reaching to distant targets (injury level C7-T4) [41]. Kim, et al. [40] concluded that these findings might be related to the need for counterbalance in SCI when stretching the arm for reaching, which means that the trunk moved in the opposite direction of the arm to maintain balance. This counterbalance could also be provided by using the other arm. Yet, the variation in movement patterns was large, which was most likely associated with the level of injury [40]. Patients with low thoracic lesions (injury level T8-T12) have grossly intact trunk muscle innervation. These patients performed better in terms of dynamic sitting stability compared to patients with high thoracic lesions (injury level C7-T7) [37, 38]. In addition, reaching distance was larger in patients with low compared to high thoracic lesions. However, no differences in quiet sitting ability were observed in patients with different (thoracic) levels of SCI by Chen, et al. [37]. Trunk length significantly influenced trunk stability [37, 38]. The center of gravity shifts upwards with increasing trunk length and, as a result, it is more difficult to maintain the center of gravity over the base of support. Comparable to the patients with CP, the limits of stability in patients with SCI (injury level above T12) were smaller when reaching laterally compared to reaching forward [39]. Interaction trunk – head In healthy children, it has been shown that head movement is not influenced by a decrease in trunk stability due to task demands [4]. This is related to the preferred head movement strategy, namely to stabilize the head in space rather than with respect to the trunk [13]. Children with CP may have both impaired trunk and impaired head