Laura Peeters

120 | Chapter 6 Measuring trunk function Physiological measures In this thesis, we used physiological measures, such as muscle strength testing, kinematic analysis and electromyography to assess trunk function. These measures give insight in the maximum capacity (maximum strength, maximum range of motion, and maximum muscle activity) and the movement and muscle activity used to perform daily tasks, but also have their limitations. Markers were placed on the participants’ back to gain insight in trunk movement. Since these markers needed to be visible for the optical infrared cameras, only participants were included who were able to sit independently without a backrest. This does not reflect the entire patient population and the daily life situation for patients seated in a wheelchair. Therefore, being able to measure trunk movement when seated in the wheelchair would have had added value, and might lead to different results with regard to trunk movement. Compensatory trunk movements might increase in early non-ambulatory patients, because the backrest can be used as a support surface for compensatory movements in the frontal plane, it provides safety from falling backwards, and reduces muscle effort needed to maintain posture. However, measuring trunk movement in multiple segments in a wheelchair is challenging, because measurement systems have to be very small and pressure resistant, so that they do not cause discomfort and generate signals without artifacts caused by sitting against the backrest. A few startup companies, like Bainisha (Bainisha cvba, Lokeren, Belgium) and Epionics SPINE (Epionics Medical GmbH, Potsdam, Germany), are developing new types of sensors based on strain gauge techniques that might be promising for future research in patients seated in a wheelchair. These systems might even make it possible to perform home based measurements or measure for a whole day to give insight in the performance in daily life. Surface EMG provides insight in the capacity used by some superficial trunk muscles, however, these muscles are thought to be mainly responsible for movement and less for stability [17]. Since we hypothesized that SMA patients needed much more of their muscle capacity to stabilize the trunk, more insight is needed into function of the deep trunk muscles. An alternative to invasive needle or fine wire EMG would be the use of imaging techniques like magnetic resonance imaging (MRI) to grade the fatty infiltration and muscle volume. This is related to loss of muscle fibers and therefore also to functional grades [18, 19]. Yet, imaging studies involving trunk muscles in DMD or SMA are scarce as described above.