Laura Peeters

16 | Chapter 1 groups, because it is influenced by the examiner’s strength [29]. The static frame myometer can overcome this disadvantage, however this technique cannot easily be used in a clinical setting since it is not portable. In this thesis, muscle strength is measured with the static frame myometer, primarily as force (N). However, because the segment length has a great influence on the effective force that can be delivered, strength was adjusted for segment length and reported as joint torque (Nm). Movement analysis In a clinical setting, quantitative movement analysis is often performed to obtain insight in (abnormal) movement patterns for either diagnostic or evaluative purposes. Several systems are available, such as video cameras, accelerometers, or optical motion capture systems. In this thesis, an optical motion capture system is used with passive markers placed at anatomical landmarks. These markers are captured with infra-red cameras to determine 3D coordinates of all markers in space. At least three single markers are needed on each body segment to define its 3D orientation and, subsequently, to calculate joint angles from two body segment orientations [30, 31]. Electromyography Electromyography is a widely applied technique for measuring electrical activity produced by the muscles during contraction [32]. For surface electromyography, sensors are placed at recommended locations above the target muscle [33]. Because sensors are placed on the skin, only activity of superficial muscles can be determined. Several outcome measures can be determined from the electrical signals, such as muscle activity onset and signal amplitude. In this thesis, we focus on the amplitude of the electrical muscle activity. Since the measured amplitude is dependent on sensor location and skin thickness, it can vary between persons [34, 35]. Therefore, we normalized the level of muscle activity level against the maximum amplitude determined during maximum voluntary isometric contraction, yielding muscle activity as percentage of the maximum muscle capacity of a specific muscle.