Saskia Baltrusch

65 Chapter 3 During load carrying no effect on objective performance was found. Although the moment around the low-back increases with carrying, due to the load in front of the body, the passive trunk exoskeleton did not improve the performance for this task. This can be explained by the fact that the support of the passive exoskeleton relies on trunk flexion to generate resistive torques in the hinge of the device. Since the carrying task does not require trunk flexion, no extra support is obtained in this task. Tasks for which we expected potential hindrance by resistance of the exoskeleton against movement, including tasks requiring participants to use a large range of motion, indeed showed a decrease in objective performance and an increase in perceived task difficulty. Especially in tasks that involved hip flexion or trunk flexion, objective performance decreased and perceived task difficulty increased. This problem of restricted range of motion can be found in all studies that asked for subjective feedback on passive lifting devices [10,20,21]. Godwin et al. (2009) [21] reported moderate ratings of hindered ROM when wearing the device. This can be compared to our results on user impression which scored between 3.1-5.9 for restriction of range of motion (see table 2). The task walking showed both, a decrease in objective performance and an increase in perceived task difficulty, indicating a need for design improvement for this task. The hindrance during walking tasks could be solved by disengaging the leg pads, an option that the most recent version of the Laevo device does already provide. The general discomfort values show that especially walking and range of motion tasks seem to be uncomfortable. Nevertheless, general discomfort did not appear to be performance limiting, since it did not show a correlation with objective performance. Besides, we did not test the effect of time period on the general discomfort and objective performance. Discomfort values might be different when testing over a longer period of time and all-day measurements may be needed to clearly assess the relationship between general discomfort and objective performance. Final user impression scores were moderately positive, the VAS values for efficacy show that participants felt moderately supported by the device (6.4) and reported a moderate back load reduction (6.3). The general interference with the performed tasks overall was reported to be low (3.3). This indicates, that a certain degree of versatility is provided, but that the support of the device can be improved for some of the tasks to diminish the negative effects on objective performance and perceived task difficulty. Therefore, further 3