Laura Peeters

32 | Chapter 2 Interaction trunk – arm Target distance and object weight have been identified as determinants of trunk involvement during reaching in healthy adults [16]. The trunk is already involved in movement when reaching at approximately 90% of arm length distance [2, 17, 18] and when performing daily tasks within arm length [19]. Healthy children up to the age of 10 years, used their trunk significantly more compared to adults when reaching forward within arm length and also showed more variability [12, 20]. Children with CP showed even more trunk movement and decreased elbow extension when performing various arm tasks compared to healthy children [20-29]. Increased trunk movement is regarded as a compensatory strategy for impaired elbow extension and supination, particularly when reaching in the sagittal plane. Even when reaching forward with the least affected side, increased trunk flexion has been reported in children with CP, albeit non-significant [28]. In addition, increased trunk rotation has been described by Kreulen, et al. [24] when performing a drinking task. With greater target distance, trunk movement increased in all planes in healthy children, but only trunk flexion increased in children with CP [28]. Increased trunk flexion was associated with more elbow extension in healthy children, whereas it was associated with less elbow extension in children with CP [28]. Besides differences in trunk movement, the movement of the reaching arm was slower and less straight, and peak velocity was lower in children with CP compared to healthy subjects [26, 30]. Postural stability has been shown to be influenced by task demands in healthy subjects [4, 18, 31]. Increased stability was seen when a large degree of precision was required (e.g. tracing task) and decreased stability when performing UE movements which perturb posture more (e.g. aiming task) [4]. Children with CP showed postural imbalance while sitting as indicated by decreased maximum reaching distances and/ or reaching performance [30, 32, 33], increased body sway [34], or a decreased Trunk Control Measurement Score [35]. Postural stability was found to be worse during task performance compared to quiet sitting in children with CP [20, 35]. However, worse postural control did not always influence the accuracy of task performance during throwing, as shown by Huang, et al. [32]. Postural stability was worse when reaching laterally compared to reaching forward in children with CP [30, 34, 35]. Saavedra, et al. [26] and Santamaria, et al. [29] studied the influence of external support on trunk stability and arm function. Adding external trunk support improved reaching performance and posture. The adequate level of support was dependent on disease severity; patients with Gross Motor Function Classification Scale (GMFCS) levels I or II already benefitted from pelvis support, whereas patients with GMFCS level V needed support at axillary level [36]. Importantly, adverse effects on reaching performance and posture were seen when the level of support was higher than the trunk level