Laura Peeters

52 | Chapter 3 12 th thoracic vertebrae (T12) and the xiphoid process. The upper lumbar segment was defined by markers on T12, spinous processes of the 3 rd lumbar vertebrae (L3) and a laterally placed marker at the level of L1/L2. The lower lumbar segment was defined by markers on L3, spinous processes of the 5 th lumbar vertebrae (L5) and a laterally placed marker at the level of L4. Data analysis Data were filtered with a bi-directional 4 th order Butterworth low-pass filter (cutoff frequency of 6 Hz). A biomechanical model was used to calculate the movements of the body segments [11]. Joint coordinate systems were based on the ISB-guidelines [12, 13].The longitudinal axis was created first for the trunk segments and the following kinematic variables were extracted using Euler decomposition in the following order: • Pelvis angle: angle of the pelvis relative to the global coordinate system (anterior/ posterior tilt – lateral tilt – axial rotation) • Individual trunk segment angles: angle of a trunk segment relative to the more caudal segment (flexion/extension – lateral bending – axial rotation). • Neck angle: angle of the head relative to the upper thoracic segment (flexion/ extension – lateral bending – axial rotation) Figure 2 Illustration of marker placement