Saskia Baltrusch

64 Chapter 3 For static holding tasks, in which we expected the user to be assisted, no increase in objective performance when wearing the exoskeleton was found. Although the change of performance for forward bending was not significant, the perceived task difficulty and the local discomfort in the lower back during this task decreased significantly by 3 units on the VAS scale, when wearing the exoskeleton. Also, the local discomfort in the upper legs (back) was reduced by 2.2 units on the VAS scale in the exoskeleton condition. This indicates that participants were able to hold the posture in both conditions, but did experience more difficulty and more discomfort, when not wearing the exoskeleton. Similar effects can be seen in the one-handed bank task. The accompanying increase in local discomfort in the chest and the trend towards increased local discomfort at the front side of the upper legs during these two tasks can be explained by the chest and the leg pads of the device. Similar results in discomfort were shown in a study by Graham et al. (2009) [10]. Their participants also reported an off-loading of the back, but did experience pressure points at the legs and shoulders, where the device was in direct contact with the user. Based on these outcomes a passive exoskeleton can be effective in assisting the user in static holding tasks, including trunk flexion. This effect might be improved in terms of wearing comfort at the contact points with the user’s body, although the magnitude of this discomfort was low. Bosch et al. (2016) [9], investigated a previous version of the Laevo device. They also found lower local discomfort in the lower back and increased local discomfort at the chest when wearing the exoskeleton in forward bending work. Opposite to our results, they did find an increase in maximal holding time. This can be explained by the difference in applied methodology. In the study of Bosch et al., (2016) [9] the researcher decided when to stop the task, based on the participants rating on the Borg Scale during the task. When the participants rated 2 (i.e. “slight discomfort”) in any of the back regions the maximal holding time was noted. In the present study, however, we had the participants decide whether and when to stop the task due to discomfort in the back. Most of them fulfilled the total 5 minutes of the task. This may have led to biased results in the maximal holding time, explaining the lack of effect of the passive trunk exoskeleton on the objective performance in forward bending in our study.