Laura Peeters

Trunk, head and pelvis interactions in healthy children | 51 3 head. Here the instruction was to keep the rest of the body as quiet as possible and only move the head. Thereafter, a series of tasks was performed with the dominant hand at a self-selected speed. No instructions were given for the other hand. Several reaching (and placing) tasks were performed: reaching forward, sideways and contra- lateral at a 45 degrees angle in the transverse plane. The subjects were asked to touch a reference frame positioned at the desired position, or to place a weight on the reference frame (Figure 1). Reaching distance, height and object weight were varied, resulting in the following combinations for forward and lateral reaching: nearby- shoulder height-0 gram (“N-S-0”), nearby-shoulder height-500 gram (“N-S-500”), far-shoulder height-0 gram (“F-S-0”), nearby-eye height-0 gram (“N-E-0”), nearby-eye height-500 gram (“N-E- 500”), far-eye height-0 gram (“F-E-0”). Contra-lateral reaching was only performed nearby-shoulder height-0 gram and nearby-shoulder height-500 gram. Nearby was defined as 100% arm length, far as 133% arm length. Arm length was defined as the distance from mid-acromion to mid-hand. Furthermore, subjects were asked to perform four daily tasks: displace a porcelain plate from left to right on a table with both hands (“Plate”), bring a cup of 200 grams to the mouth (“Drink”), trace a path with a pencil (“Draw”) and place a finger on a number diagram while holding the diagram with the other hand (“Dexterity”). The drink, draw and dexterity task were based on the instructions of the Performance of the Upper Limb [9]. No instructions were given on how to perform the tasks. Data acquisition Marker positions were recorded at 100 samples/s using an optical motion capture system (Vicon, Oxford, UK). Twenty-five reflective markers were placed on the skin to define the position of the head, trunk, pelvis and both arms (Figure 2). The trunk was divided into four segments (upper thoracic, lower thoracic, upper lumbar and lower lumbar) to obtain a detailed representation of trunk movement [10]. Markers on the head, pelvis and arms were placed according to the Vicon Plugin-Gait model. For 15 subjects, two additional markers were placed on both sides on the iliac crest, as we noticed that the anterior superior iliac spine markers often became invisible when flexing the trunk or moving the arms. The upper thoracic segment was defined by markers on spinous processes of the 7 th cervical vertebrae (C7), spinous processes of the 6 th thoracic vertebrae (T6), jugular notch and xiphoid process of the sternum. The lower thoracic segment was defined by markers on T6, spinous processes of the Figure 1 Reference frame with 500 gram weight used for performing the reaching tasks.