Laura Peeters

106 | Chapter 5 for SMA, and the average abdominal muscle activity was respectively 10% of MVIC and 44% of MVIC. In addition, median muscle activity for the deltoid muscle was around 100% MVIC and was significantly greater (p<0.05) compared to HC. Case 6 years old participant In general, little differences were found between SMA_6y and HC_6y. Both joint torque and maximum active range of trunk motion were comparable between the 6 years old participants. Trunk ROM of SMA_6y was different from the HC_6y in half of the daily tasks. However, both increased and decreased ROM was seen, and in the majority of tasks the difference was less than 3 degrees. Variability in normalized muscle activity for HC_6y was too large to reliably compare with SMA_6y. DISCUSSION This is the first study describing trunk function in SMA in relation to the performance of upper extremity tasks. Demand on trunk muscles is high when performing such tasks, reflected by increased normalized muscle activity levels as hypothesized, but in contrast with our hypothesis this occurred without an increased trunk range of motion. Trunk joint torque was decreased in patients with SMA compared to HC with at least a factor two in median value. Additionally, SMA type 2 patients seemed weaker in trunk torque compared to type 3, as was also found previously [4]. On the other hand, the large interquartile ranges indicate a gradual scale in trunk function, which is in line with the fact that SMA shows a range of functional abilities rather than absolute differences between types of SMA [5]. More patients are needed to confirm whether there is a difference between types or that it is a graduate scale. Maximum active trunk ROM was limited in patients with SMA compared to HC in all directions. To perform the ROM tasks, both groups used a comparable percentage of their maximum muscle capacity for the muscles counteracting gravitational moments in flexion, extension and lateral bending movements. This indicates that patients with SMA achieve a lower maximum ROM when using similar muscle effort of the counteracting gravitational muscles as HC. This is not surprising, since the maximum absolute muscle activity is much less for patients with SMA due to loss of motor neurons. A lower maximum absolute muscle capacity results in less force generating capacity, as reflected in the decreased joint torques. When performing reaching and daily tasks, patients with SMA used a greater percentage of their maximum trunk muscle capacity compared to HC, although