Saskia Baltrusch

63 Chapter 3 The issues addressed in the user’s impression questionnaire and their respective median values are presented in Table 2. Adjustability, including donning and doffing and length adjustment, was rated as easy to moderate. Range of motion with the device did also receive moderate values. The efficacy of the device in terms of reduction of back loading and support of the tasks was experienced as limited. The interference of the exoskeleton with the tasks was considered to be low. For more detailed information see Appendix 1. 4 Discussion The main goal of this study was to evaluate the effect of a passive trunk exoskeleton on the functional performance in healthy individuals. We expected an increase in the functional performance in the tasks in which the user’s trunk is supported against gravity. In addition, we expected a decrease in functional performance in the tasks in which the user is required to use a large range of motion, which might be hindered by resistance generated by the exoskeleton. We expected an increase in the objective performance (maximal weight lifted) and a decrease in perceived task difficulty for lifting, considering studies that found reduced back loading during lifting when wearing assistive devices [8, 10-12]. However, neither objective lifting performance nor the perceived task difficulty showed any difference between exoskeleton and control condition. A possible explanation is likely found in a ceiling effect due to the limited maximal load mass (23 kg) that we used. This limitation was due to the fact that we were not allowed to exceed limits proposed in the NIOSH guidelines. The unchanged perceived task difficulty, while wearing the device, might further be explained by some problems participants experienced when lifting from the ground. Shifting or turning of the chest pad, leading to general discomfort and upward shifts of the whole device occurred, resulting in an inefficient functioning of the exoskeleton. The results from the user’s impression questionnaire related to adjustability also indicate that problem, showing values ranging from 2.1 to 6.9 for length adjustment of the exoskeleton. These problems might outweigh any potential positive effect as a result of low back load reduction. This could be solved by an improved adjustability of the device to the different user’s physiques. 3